DXNest Motion:
the mechanism constructor

The work is always the same four actions, repeated in a loop:

1. Draw it. Pick a tool in the left palette and click on the sheet. Each tool adds a complete structural group — a crank, a dyad, a slider group, a gear train.
2. Set the sizes. Type exact lengths, coordinates and angles in the right-hand panel, or double-click the dimension right on the drawing.
3. Let it solve. The calculation starts by itself after every change. The status bar reports the residual of the solution, for example Residual 9.98e-8 mm.
4. Read the result. The animation, the Analysis tab, the Graphs window, or an export to DXF, Excel, CSV or an image.

Username

Your user name — not your display name. The line under the form says so too.

Password

Your password.

Sign in

Signs you in. Enter in either field does the same.

Open the demo

Demonstration mode: the whole program works, but files are turned off and the charts carry a watermark. See section 19.

4.1Document and export

New mechanismnew tab

Creates an empty document in its own tab. The mechanism you were working on stays open and solved.

Openopen JSON

Opens a mechanism .json file from disk. If the current tab already has something drawn in it, the file opens in a new tab; an empty document is replaced in place. Turned off in the demo.

Save as JSONsave

Saves the active mechanism to a file. In Chrome and Edge the system “Save as” dialog opens, so you choose the folder and the name yourself; in other browsers the file simply lands in the downloads folder, and the status bar says so. The default name is the mechanism name. The file structure is section 17.

Export imagepicture

Opens a menu with three formats: PNG, JPEG, SVG. The current frame is exported in the current theme — the drawing comes out on the same sheet you are looking at.

Export DXFCAD drawing

One solved frame in AutoCAD R12 format: links as lines on layer LINKS, pairs as circles on POINTS, labels on LABELS.

Export ExcelXLSX workbook

A workbook with one sheet per kinematic pair, link, segment and roller, a chart for every parameter, and a contents sheet.

Graphsgraph window

The large kinematic-diagram window. It plots curves from every open tab over each other. Active only after a solution exists.

Private projectsserver

Your own library of mechanisms on the server, visible only to your account.

Recalculatesolve again

Forces a fresh solve. The icon spins while it runs. Rarely needed: the calculation starts by itself after every change.

4.2Tools after the separator

Selectarrow

The ordinary mode: selecting objects, dragging supports and dimensions, double-clicking to edit. This is the default state, and Esc always brings you back to it.

Linear dimensionlength

Places a dimension between two points of the drawing. The tool stays armed after each dimension, so a whole drawing is dimensioned in one run.

Angular dimensionangle

The angle between two rays from a shared vertex. Angular dimensions are always informative — they cannot be made driving.

4.3The right-hand end

Themesun / moon

Switches the whole program — toolbar, panels, inspector and the drawing sheet — between the dark and the light palette. The choice is remembered for next time.

Adminservice

Account management. This button exists only for administrators — it plays no part in ordinary work, and most people never see it.

Sign outleave

Leaves the program. Unsaved mechanisms are lost — save them to a file or to server projects first.

Click the name

Switches the active document.

Double-click

Renames the mechanism in the tab itself: the name turns into an input field with the text selected. Enter confirms, Esc cancels, clicking away also saves. An empty name is refused and the old one stays.

The ×

Closes the document. The last tab cannot be closed — it is replaced by an empty document.

The + on the right

The same as New mechanism on the toolbar.

The dot before the name

Green — the mechanism is solved; grey — there is no solution yet.

The chosen tool is outlined. Hovering over a button shows its name. While a tool is armed, the status bar says which click it is waiting for.

Esc or Enter cancels a construction in progress. Pressing it again returns to Select.

The order of construction

A mechanism grows outward from its drive. Start with Input crank — it establishes the fixed support, the driving link and the rotation. After that every tool attaches to a kinematic pair that already exists.

6.1Family 1 — linkage groups

Input crankthe drive

A fixed support, a driving link and a rotation drive. Every mechanism starts here. Two clicks: the support, then the moving pair.

Dyadtwo-link group

Two links and an intermediate pair, closed onto a new fixed support. The classic Assur group of the second class — with a crank it makes a four-bar linkage.

Slotted Link Mechanismslotted lever

A pivoted slotted lever: the crank pin slides inside the slot of a lever that turns about its own fixed support.

Slider grouprod and block

A connecting rod and a block on a guide. The guide can be anchored to an existing pair, and its axis then snaps to multiples of 15°.

Two-link slider groupwith an intermediate pair

An intermediate pair first, and only then the rod with its block. The first link is oriented relative to its parent, so the group adds no unintended degree of freedom.

Relative linkone rigid link

A single rigid link from an existing pair to a new point. Defined by a length and an angle to its parent link.

Point on link or geartracer point

A point rigidly tied to a link or to a wheel. It adds no equations — it simply gives you a trajectory, a velocity and an acceleration where you need one.

6.2Family 2 — gears and special assemblies

Gear trainany number of wheels

One train of as many wheels as you need, a wheel per click. The distance to the click sets the centre distance, and from that the radii.

Gear sector transmissiontoothed sector

A sector on a fixed support meshed with a wheel on a moving pair. If the carrier turns a full revolution, a complete wheel is inserted instead of a sector.

Internal gear transmissionring and pinion

A ring with internal teeth and a pinion inside it. Three clicks: the axle, the ring radius, the pinion position.

Moving wheel / fixed rackwheel on a rack

A wheel rolling along a fixed rack, together with an output pair on it. Attaches to a slider pair.

Moving rack / fixed wheelrack on a wheel

A moving rack on the block turns a wheel with a fixed axle.

Eccentric drivedisc and pin

A disc on a shaft with a pin on the eccentricity radius. The pin is an ordinary moving pair and carries the next group.

Pressing segmentrolling sector

A cylindrical sector that rolls without slipping over a flat form while a carriage roller drives it along — the working member of a flat-cylinder die-cutting press.

Roller on wheelrim clearance

Measures the clearance between two rims through the cycle. It adds no equation of its own until the contact is switched to Rigid.

7.1What is drawn on the sheet

7.2Moving around the sheet

Zoom incloser

Enlarges by 18 % about the centre of the sheet. The maximum is ×6.

Zoom outfurther

Reduces by the same 18 %. The minimum is ×0.25.

Reset viewback to default

Restores ×1 zoom and zero offset. Useful when the drawing has wandered off the sheet and you cannot find it.

Action	Result
Mouse wheel	Pans the sheet.
Ctrl / ⌘ / Alt + wheel	Zooms under the cursor. Between ×0.25 and ×6.
Middle-button drag	Pans.
Zoom in / Zoom out	Steps of ×1.18 about the centre of the sheet.
Reset view	Returns the zoom and the position to their defaults.

7.3Mouse actions on the drawing

Click a link or a dimension

Selects the corresponding object — it is highlighted both in the list on the right and on the drawing.

Drag a support

A fixed support can be dragged on the drawing itself. When you let go, the new coordinates pass through the solver: if they contradict a fixed dimension, the support returns to where it was.

Drag a segment centre

The centre of a pressing segment is dragged the same way; where you drop it sets both of its radii and which way it leans.

Drag a dimension

Any dimension can be pulled to a clearer place. It remembers that offset.

Double-click a dimension

Opens the box for typing an exact value (section 13.3).

Double-click a support

The X / Y coordinate box for that support.

The guide rotate handle

Lets you turn the axis of a slider guide with the mouse; the travel is recomputed over the whole cycle.

The tool name in that readout is the complete list of states the program can be in:

7.4Snapping and alignment

While you move the cursor during a construction, the program pulls the point to a “round” position by itself. There is nothing to configure — it always works.

7.5Prompts on the sheet

While a tool is armed, the top-left corner of the sheet says in yellow which click is expected. The prompt changes at every step. The complete list:

Every prompt ends with (Esc or Enter — cancel), and the gear train with (Esc or Enter — finish the train).

8.1The left side — messages

8.2Display switches

Grid

A coordinate grid on the sheet. Off by default.

Dimensions

Dimensions and support coordinates. Switch them off when the scheme gets crowded — it changes nothing in the calculation.

Velocity

Green velocity vectors at the pairs. On by default.

Acceleration

Acceleration vectors. Off by default, because their scale is usually much larger.

Units

mm or inch. This changes only display and input; the file always stores millimetres.

8.3Confirmation messages

Besides errors, the status bar confirms what has just happened. These are all of them:

9.1Object list

The tree shows the mechanism as it was built: the document at the root, structural groups below it, and inside each one its pairs, links, drives, sliders and wheels. Clicking a row selects the object both on the drawing and in the parameters panel.

The chevron beside a group

Collapses and expands the branch. Selecting a child from the drawing opens its group by itself.

Hollow circle

A kinematic pair.

Chain link

A link.

Circular arrow

A rotation drive.

Sliders icon

A slider group.

Gear icon

A toothed element or a rack.

What the panels say when they are empty

9.2Animation strip

▶ / ❚❚

Plays and pauses the animation. The mechanism runs through the frames of the solved cycle.

↻ Reset

Returns to frame 0.

Position

Every position of the cycle in degrees of crank angle. Pick one to stop at exactly the angle you need.

Speed

Playback speed: ×0.1, ×0.25, ×0.5, ×1, ×2, ×4. It does not affect the rotational speed used in the calculation — only what you see on screen.

Set current position as initial

Makes the current pose the initial one: the current angle is written into every drive, so the frame you stopped at becomes φ = 0°. Useful when the mechanism assembled in a pose other than the one you want to measure from. The status bar then confirms: “The current mechanism position is now the initial position (φ = 0°)”. The button is disabled until the mechanism has been solved.

9.3How the parameter fields work

There are three kinds of field, and they behave differently. Learn them once and every form afterwards reads the same way.

Text field

The simplest: Name and the like. The value takes effect as you type.

Drop-down list

A choice from a fixed set: Start pair, Rotation source, Symbol. The change takes effect at once and triggers a fresh solve.

Dimension field

The important one. This field does not merely store a number — it asks the solver to achieve that number.

The padlock beside the caption

Switches the dimension between floating (open padlock) and driving (closed). The solver may not change a driving dimension and fits everything else to it; on the drawing it is boxed. The button's own tooltip says it plainly: “Fixed dimension — click to make floating”.

The ▲ ▼ arrows

Nudge the value by one step. The step follows the units: 1 mm, 0.01 inch or 1°. The button tooltip shows the exact step.

↑ / ↓ in the field

The same as the arrows, from the keyboard. If you have already typed something, the step is taken from what you typed.

Enter

Applies what you typed.

Esc

Restores the previous value without applying anything.

A leading =

Binds the field to a formula. The field then shows the expression itself (=R*2.9) and the stepper arrows disappear — the formula owns the value now, and stepping it would silently break the binding.

Red outline

What you typed does not read as a number or an expression, or it is below the allowed minimum (a link length cannot be 0, for instance).

Red text under the field

The number was read, but the mechanism will not assemble at that value. A Calculate feasible range button appears alongside it to work out the interval where the value is possible.

9.4Parameters by object type

The form depends on what is selected. Common to all of them: a Name field at the top and a red Delete selected button at the bottom (except for the document root).

Document — Mechanism

The only field is the mechanism name. It also becomes the tab title, the default file name when you save, and the caption in the Excel workbook.

Kinematic pair — Point

X, Y

Coordinates. For a fixed support this is a real dimension with a padlock. For a moving pair it is only the solver's starting guess — its true position comes from the solution.

Fixed support

Switches the pair between moving and fixed. Clearing it on a support releases a degree of freedom, and the mechanism may stop closing.

A point on a link has no coordinates of its own. One distance along the link defines it:

Measured from

Which end of the link to measure from.

Distance from…

The distance. A value greater than the link's length puts the point on its extension — which is exactly how a rigid overhang is drawn.

Link — Link

Start pair / End pair

The pairs the link joins. Changing them re-hangs the link on other points.

Length, mm

The link length — the main dimension of a mechanism. With the padlock closed it becomes driving.

Relative to

The link this one's angle is measured from. None — the angle is free and only the length holds the link.

Angle to parent

Appears as soon as a parent link is chosen: the angle between this link and its parent. Together with the length it pins the position completely — this is how rigid overhangs and rockers are defined.

Drive — Driver

Base pair / Moving pair

The fixed axle and the pin that turns about it.

Length

The crank radius. It is edited as the length of the paired link, so the two values cannot drift apart. If the drive belongs to an eccentric disc, the field is called Eccentricity λe and edits the disc's eccentricity — again, the two cannot drift apart.

RPM

Rotational speed in revolutions per minute. It scales the velocities and accelerations in every result.

Initial angle, °

The angle from the horizontal to the crank at position 0°.

Rotation direction

Counter-clockwise (+) or Clockwise (−).

Show rotation direction arrow

Whether to draw the red direction arc beside the support.

Slider group — Slider

Sliding pair

The pair that slides in the guide.

Guide origin

Free coordinates — the guide stands at its own coordinates. Choose a pair instead and the guide passes exactly through it and travels with it.

Origin X / Origin Y

The point the guide axis runs through (when it is not anchored).

Axis angle

The angle of the guide axis to the horizontal.

Stroke (travel)

The block's travel over the cycle. This is a dimension too: fix it and the program fits the rest of the geometry to the stroke you asked for.

End 1 / End 2

The coordinates of the two travel limits. Each can be fixed separately — a convenient way to specify a press “from” and “to”.

Symbol

How to draw it: Block slider or Roller between guides. This affects the symbol only — the kinematics are identical.

Rack — Rack

Carrier pair

The pair that carries the rack. For a moving rack this is the slider pair; a fixed rack is bolted to the frame and has no such field.

Length

The rack's length. Drawing only — the mesh is computed along the line, not along the segment you see.

Tooth pitch

The tooth pitch. It must match the mating wheel, or the teeth will visibly disagree on the drawing.

Centre X / Centre Y

The coordinates of the rack's midpoint. These are full dimensions with padlocks — a rack is positioned exactly like a slider guide.

Axis angle

The rack's angle to the horizontal.

The note line

Reminds you that the centre and both ends of a rack can be picked by the dimension tools, so its position can be driven by a dimension.

Structural group — Group

Name / Type

A free caption and the group's kind. Both are just text for the tree and the exports.

Attached pair

The pair the group hangs on. Changing it moves the whole group to another place in the mechanism.

Points / Links

How many pairs and links the group contains.

Slider guide

If the group contains a block, the whole set of its guide fields is repeated here — no need to hunt for the slider in the tree.

9.5Deleting objects

Delete selected removes whatever is selected. But a mechanism is not a list: everything in it holds on to everything else, so deleting always takes with it whatever no longer makes sense. The rules are:

10.1Input crank — the drive

The first tool in any mechanism. It adds three things at once: the fixed support O1, the moving pair A1, and a rotation drive.

1. Click Input crank in the palette. The status bar says: “Place the moving pair to set the crank length and direction”.
2. The first click places the fixed support.
3. The second click places the crank pin. The distance between the clicks becomes the crank length, the direction becomes its initial angle.

Limit: the pin must be at least 10 mm from the support, or the status bar says “Place the crank pair at least 10 mm from its support”.

10.2Dyad

Two links and an intermediate pair, closed onto a new fixed support. With a crank this makes the classic four-bar linkage.

1. Arm Dyad and click an existing kinematic pair to attach the group to (usually A1).
2. The second click is where the intermediate pair goes — at least 20 mm from the attachment pair.
3. The third click is where the new fixed support goes.

10.3Slider group

A connecting rod and a block on a straight guide. This already makes a slider-crank mechanism.

1. Arm Slider group and click the pair the rod attaches to.
2. The second click places the block. The direction from the pair to the click sets the guide angle.

Anchoring the guide to an existing point

The guide can be seated exactly on an existing pair or support. Then there are three clicks:

1. The pair the rod attaches to.
2. Click an existing pair or support — the guide origin lands exactly on it, and the axis snaps to multiples of 15° as the cursor moves.
3. The third click only picks the block's position along that line.

10.4Two-link slider group

The same thing but with an intermediate pair: first a short link from the parent pair, and only then the rod with its block.

1. Click a pair that belongs to an existing link — this tool cannot attach to a pair that is joined to nothing.
2. The second click places the intermediate pair (at least 15 mm away).
3. The third click places the block and its guide angle.

10.5Slotted Link Mechanism

The crank pin slides in the slot of a lever that rocks (or turns) about its own fixed support.

1. Arm Slotted Link Mechanism and click the moving pair that will become the sliding block.
2. The second click places the lever's fixed pivot.

A slotted link has no parameters form of its own — it is made of ordinary objects. The lever is a link and is edited as one; the block is an ordinary pair; the pivot is a fixed point. The whole group appears as one row in the tree.

10.6Relative link

A single rigid link from an existing pair to a new point. Used for overhangs, rockers and any rigid extension.

1. Arm Relative link and click the starting pair.
2. The second click places the far end of the link.

10.7Point on link or gear

The simplest and the most useful tool: it places a point rigidly tied to a link or a wheel, so you can read its trajectory, velocity and acceleration.

1. Arm Point on link or gear.
2. Click the link itself (not a pair), or the body of a gear wheel.

The same tool on a wheel makes an arm

Click the body of a gear wheel instead of a link and the program adds not just a point but an arm: a link from the wheel axle to a new pair. That pair turns with the wheel and carries the next group — this is how motion is taken off a gear transmission.

11.1Gear train

One tool builds a train of any number of wheels, and the whole train stays one object in the list. Wheels are not defined by radii — they are defined by centre distances, that is, by where you click.

1. Arm Gear train and click the axle the train starts from: a fixed support, or a pair moving on an arc about a fixed support.
2. Click where the second axle goes. The distance is split into the two initial pitch radii.
3. Every further click adds one more wheel: the distance to it minus the previous wheel's radius gives the new radius.
4. Enter or Esc finishes the train.

Limits: a wheel can only go on a fixed axle. Clicking a moving pair gives “That pair moves, so no wheel can be mounted on it”. Clicking an axle that already carries a wheel from another train asks you to change its Rotation source instead.

11.2Gear sector transmission

A transmission between a moving pair and the support it swings about: a sector on the support, a wheel on the moving pair, and an output pair on the wheel that carries the next group.

1. Arm Gear sector transmission and click a pair that moves on an arc — the rocker of a four-bar, for instance.
2. The second click sets the direction the mating element takes.

11.3Internal gear transmission

A ring with internal teeth and a pinion inside it. This is the one transmission whose size does not follow from the distance between two axles, so it is drawn the way it is dimensioned: the rim first, then the pinion within it.

1. Arm Internal gear transmission and click the ring's axle.
2. The second click sets the ring radius. The status bar tells you the minimum that still leaves room for a pinion.
3. The third click places the pinion axle inside the rim: whatever is left of the ring radius becomes the pinion's own.

11.4Rack transmissions

Both rack tools attach only to a slider pair — build a slider group first.

Moving wheel / fixed rack

1. Arm Moving wheel / fixed rack and click the slider pair.
2. The second click chooses which side of the wheel receives the fixed rack.

Moving rack / fixed wheel

1. Arm Moving rack / fixed wheel and click the slider pair — the rack goes on it.
2. The second click sets where the fixed wheel's support stands beside the rack.

11.5Parameters of a toothed element

Toothed element

Gear wheel, Pinion, Gear sector or Internal ring gear. It changes only how the element is drawn and which fields are offered.

Centre pair

The pair the wheel's axle sits on.

Output pair

The pair on the wheel that carries the next group, if there is one.

Rotation source

The key field — see the table below.

Engagement

For a mesh with another wheel: External engagement — the wheels turn opposite ways; Internal engagement — both turn the same way.

Pitch radius / Teeth

The pitch radius and the tooth count. The radius is a full dimension with a padlock.

Sector start / span, °

For a sector: where the toothed arc begins and how wide it is.

Eccentricity / Eccentricity angle

Offset of the wheel's geometric centre from its axle — for non-circular and eccentric wheels.

Phase, °

The wheel's initial rotation angle.

Arm angle to…

Replaces Phase when there is an output pair: the angle the arm stands at on the wheel. Turning it moves the arm on the wheel, not the wheel — so the teeth stay meshed.

Output pair radius

Appears with an output pair: the radius the pair is held at. If an arm link carries the pair, this field edits that link's length and is named after it.

Gear ratio (automatic)

For a mesh: the ratio computed from the pitch radii. Read-only.

Rotation multiplier

For a drive from a link: how many times faster the wheel turns than the link. A negative value reverses it.

Direction

For a fixed wheel: the sign of rotation, 1 or −1.

Below the fields are note lines that explain the wheel's current state: how it is driven and what ratio applies, plus two important warnings that appear when they matter:

• The axle is held by the mesh. If the wheel sits on an axle that only the mesh holds apart, changing either pitch radius carries the axle to the new centre distance, and dragging the axle swings it round the mating wheel instead of away from it.
• The arm angle. Explains where Arm angle is measured from, and that turning it moves the arm on the wheel rather than the wheel. Fix it to keep that angle while other dimensions are driven.

Rotation source — what turns the wheel

When the source changes, the wheel's current angle is preserved, so the picture does not jump. Press Play to see the result.

12.1Eccentric drive

A disc on a shaft with a pin on the eccentricity radius. The pin is an ordinary moving pair, and it is what carries the next group.

1. Arm Eccentric drive.
2. The first click is the shaft. Clicking an existing pair mounts the disc on that shaft and takes its rotation from whatever already turns it. Clicking empty space creates a new support with its own drive.
3. The second click places the pin: the distance is the eccentricity, the direction is the disc's initial angle.

Shaft pair

The shaft the disc sits on.

Pin pair

The pin on the eccentricity radius — an ordinary moving pair that carries the next group.

Rotation source

Where the disc takes its rotation: its own drive, the link it is mounted on, or a wheel on the same shaft.

Eccentricity λe

The radius the pin sits at. A full dimension with a padlock.

Initial angle

The disc's angle at φ = 0°.

Disc radius (drawing)

The disc radius for drawing only. It has no effect on the kinematics — reduce it if the disc hides the scheme.

RPM

Appears when the disc has its own drive: the shaft speed in rev/min.

Rotation direction

Also for its own drive only: counter-clockwise or clockwise.

12.2Roller on wheel

Measures the clearance between a roller rim and a wheel rim through the whole cycle. The radii are fitted so that the rims touch exactly at the closest approach.

1. Arm Roller on wheel and click the pair that carries the roller.
2. The second click is the pair the wheel is mounted on.

Roller pair

The moving pair that carries the roller.

Wheel pair

The pair the wheel sits on.

Roller radius r

The roller's radius.

Wheel radius R

The wheel's radius.

Engagement

Roller outside the wheel (R + r) — the roller runs on the outside of the rim, so the centre distance is the sum of the radii. Roller inside the wheel (R − r) — the roller runs inside the rim and the distance is the difference.

Contact

Measured — reports the clearance only — the pair constrains nothing and cannot redefine the mechanism. Rigid — holds the rims in contact — it holds the centre distance like a link and costs one degree of freedom.

The note lines

The contact centre distance, the clearance in the current position, and the closest approach over the whole cycle. A rigid contact adds a reminder that it costs one equation.

The clearance series is in the Analysis tab (the Roller sub-tab), in the Graphs window, and in the XLSX export.

12.3Pressing segment

The working member of a flat-cylinder die-cutting press: a cylindrical sector rolls over the flat form without slipping while the carriage roller, seated in its concave guide, drives it along.

1. First build the drive that moves the carriage — usually a crank with a slider group.
2. Arm Pressing segment and click the carriage pair that carries the pressing roller. It must be a moving pair, not a support.
3. The second click is on the flat form the segment has to roll over.

Why the segment adds no degree of freedom

Two contacts define its pose completely:

Centre pair

The pair that is the segment's centre. Its position is not given by coordinates — it is given by the two radii below.

Carriage pair (pressing roller)

The moving carriage pair that carries the pressing roller.

Centre X / Centre Y

The coordinates of the segment centre. Not ordinary coordinates: across the form the number goes into the working radius R, along the form into the guide radius R₁. Both follow the point you ask for.

Working radius R

The working radius — the radius it rolls on.

Arc span, °

The angular length of the segment's arc.

Roller guide radius R₁

The radius of the concave guide the roller sits in.

Roller radius r₁

The carriage roller's radius.

Shell thickness

Wall thickness — drawing only.

Body start angle, °

Where the drawn body of the segment begins.

Form length

The length of the flat form.

Form angle

The form's inclination to the horizontal.

Form centre X / Y

The coordinates of the form's midpoint. Positioned exactly like a slider guide, and can be driving dimensions in the same way.

Segment side of the form

Three values: None — free rolling, Left of the form axis (above a level form), and Right of the form axis (below a level form).

Anti-slip rack

Drawn along the form or Hidden. Drawing only.

The note lines

A reminder of γ = S / R, the roller offset R₁ − r₁, the segment height h = R(1 − cos(span/2)) in millimetres and as a fraction of R, and the swing over the current carriage stroke.

The segment's angular displacement, velocity and acceleration are in the Analysis tab (the Segment sub-tab), in Graphs, and in the XLSX export.

13.1Dimensions the program places itself

These appear on the drawing automatically and are not “added” anywhere — they belong to the objects themselves:

13.2Added dimensions

Two tools on the main toolbar place your own dimensions between any points of the drawing. Both stay armed after each dimension, so a whole drawing is dimensioned in one run; Esc ends the run.

Linear dimension

1. Arm Linear dimension.
2. Click the first point: a kinematic pair, a support, or a slider travel end.
3. Click the second point.
4. Click where the dimension line should run. Its position decides what kind of dimension it is — aligned, horizontal or vertical, the way dimensioning works in AutoCAD.

Angular dimension

1. Arm Angular dimension.
2. Click the vertex of the angle.
3. Click a point on the first ray, then on the second.
4. The last click sets the arc radius.

Every added dimension collects in the Dimensions tab, where you can rename it, change its reference points, its measuring mode and its value.

Name

The dimension's caption in the list.

From / To

The two reference points. For an angle: Vertex, Ray 1, Ray 2.

Measure

Distance (aligned), Horizontal (ΔX), Vertical (ΔY).

Value

The value. With the padlock closed the dimension becomes driving and the mechanism is fitted to it. If a dimension cannot be driving, the field shows the value in brackets as a reference.

The bin

Deletes the dimension together with its fixed state and its formula.

13.3The dimension box

Double-clicking any dimension on the drawing opens a small box right beside it.

The value field

A number in the current units. A formula can be typed instead — any string starting with = (section 14).

Fixed (driving) dimension

Makes the dimension driving. It is boxed on the drawing at once.

OK

Applies it. While the fitting runs, the box shows “Calculating dimensions…”.

Cancel / Esc

Cancels and aborts the fitting.

Enter

The same as OK.

13.4When a dimension is impossible

If the mechanism will not assemble at the value you asked for, the box does not close: it shows the reason and offers to work out the range in which the value is possible after all.

What to do:

• press Calculate feasible range — the program probes values and reports the interval where the dimension is achievable;
• type a different number;
• unlock another dimension to give the solver more freedom.

13.5How many dimensions can be fixed

As soon as the mechanism has even one driving dimension, a balance line appears above the parameters form:

“Fixed dimensions need N floating parameter(s); M of K are floating” — the fixed dimensions require N free parameters, and M out of K are still free.

While M ≥ N the line is calm. Once there are too many fixed dimensions it turns a warning colour: the solver has nothing left to move, and the next dimension will not go through. Unlock something less important.

13.6Dragging dimensions

Any dimension can be picked up with the mouse and pulled somewhere it does not get in the way. It remembers that offset, and the rest of the dimensions stay where the program put them. For an angular dimension, dragging changes the arc radius.

+

Adds a row. The name is filled in automatically: A, B, C…

Name

The variable name. Letters, digits and underscores only; the first character must be a letter.

Formula

The expression. It may reference other variables.

Value

The computed value. err means the expression cannot be read or forms a cycle.

The bin

Deletes the row.

14.1What an expression may contain

14.2Binding a dimension to a formula

In any dimension field — in the parameters panel or in the box on the drawing — type an expression that begins with an equals sign:

=R*2.9      // coupler length = 2.9 crank radii
=A*cos(B)   // cosine in degrees
=max(L,120) // never shorter than 120 mm

15.1The Analysis tab

At the top, the Charts heading and the number of positions in the cycle. The download button beside it exports the CSV of the current sub-tab.

Below it, the sub-tab switch. Point and Link are always there; Segment and Roller appear only when the mechanism contains those objects.

Then a picker for which pair or link to show, a block of instantaneous values at the current frame, the small charts, and a table over the whole cycle.

Anatomy of a small chart

X axis

Always a full revolution: labelled 0° and 360° at the ends.

Y axis

Auto-scaled; only the minimum and maximum of the series are labelled.

The dashed vertical

The current animation frame. Run the animation and the line follows it.

The coloured marks on top

The legend: which series are drawn.

The ⤢ button

Open in Graphs window — opens the same curves in the large graph window. Clicking the chart itself does the same.

The ⤓ button

Save SVG — saves this small chart as a vector file.

Which chart is where

The table at the bottom lists every position of the cycle. The current frame's row is highlighted — run the animation and the highlight follows. The table scrolls on its own, independently of the panel.

15.2The Graphs window

The Graphs button on the main toolbar opens the large kinematic-diagram window.

1. Expand the node you need in the tree on the left.
2. Click a parameter — the curve appears on the field and its colour lights up beside the name.
3. Add as many curves as you like; a counter of selected items appears on the node.

The title field

The diagram's name. It is printed on the graph itself and carried into the exported picture.

Settings

Opens the axis and grid settings.

PNG / JPEG / SVG

Saves the diagram as a picture. Active only when at least one curve is selected.

Shift minimum displacement to 0

Shifts displacement curves so that their minimum sits at zero — handy for comparing strokes of different points.

Closing

The × in the top-right corner, or a click on the backdrop outside the window.

17.1The top level

{
  "name": "Rehei toggle press — eccentric drive",
  "settings": { "steps": 360, "inputSpeedRpm": 60, "units": "mm", "playbackSpeed": 18 },
  "points": [ … ],           // kinematic pairs and supports
  "links": [ … ],            // links
  "drivers": [ … ],          // rotation drives
  "sliders": [ … ],          // slider guides
  "slottedLinks": [ … ],     // slotted levers
  "gears": [ … ],            // toothed elements
  "racks": [ … ],            // racks
  "segments": [ … ],         // pressing segments
  "eccentrics": [ … ],       // eccentric discs
  "rollers": [ … ],          // roller contacts
  "groups": [ … ],           // structural groups for the tree
  "attachedPoints": [ … ],   // points on links
  "extraDimensions": [ … ],  // added dimensions
  "variables": [ … ],        // the variables table
  "paramLocks": { … },       // which dimensions are driving
  "formulas": { … },         // which dimensions are bound to formulas
  "dimensionOffsets": { … }  // where dimensions were dragged to
}

17.2The records inside the arrays

points — kinematic pairs

{ "id": "O1", "label": "O1", "x": 148.052668, "y": 134.463405, "fixed": true }

id is the internal key every other record refers to. label is the caption on the drawing. fixed says whether it is a support. For a moving pair the coordinates are only a starting guess.

links — links

{ "id": "L1", "label": "Eccentric rod AE", "a": "E", "b": "A", "length": 105.0, "mass": 1 }

a and b are the ids of the pairs at the ends. length is in millimetres.

drivers — rotation drives

{ "id": "D1", "label": "Eccentric shaft", "basePointId": "O1", "pointId": "E",
  "length": 45.0, "phaseDeg": -39.126927, "direction": 1, "rpm": 60 }

direction: 1 counter-clockwise, -1 clockwise. phaseDeg is the crank angle at position 0°.

sliders — slider guides

{ "id": "S1", "label": "Plate guide", "pointId": "B",
  "originPointId": "O2", "originX": 0.0, "originY": 0.0, "axisDeg": 90.0, "offset": 0.0,
  "travelMin": 344.651664, "travelMax": 399.163891, "guidePadding": 24, "symbol": "block" }

originPointId is the pair the guide is anchored to (empty when it stands at its own coordinates). travelMin / travelMax are the travel limits along the axis. symbol is block or roller.

gears — toothed elements

{ "id": "GR9", "label": "Drive gear 9", "kind": "wheel", "centerPointId": "O9",
  "pitchRadius": 90.0, "teeth": 36, "toothModule": 5.0,
  "motion": { "type": "link", "linkId": "L0", "ratio": 1.0, "phaseDeg": 0.0 } }

kind: wheel, pinion, sector, ring. motion.type: fixed, link, gear, rollingRack, drivenRack — the same choices as the Rotation source field.

eccentrics — eccentric discs

{ "id": "EC1", "label": "Eccentric drive", "centerPointId": "O1", "pinPointId": "E",
  "eccentricity": 45.0, "discRadius": 81.0,
  "motion": { "type": "driver", "driverId": "D1", "phaseDeg": 0.0 } }

rollers — roller contacts

{ "id": "RL1", "label": "Roller on wheel", "pointId": "A", "wheelPointId": "O1",
  "radius": 14.5, "wheelRadius": 45.5, "contact": "external", "rigid": false }

rigid: false — the contact only measures the clearance; true — it holds the centre distance like a link.

segments — pressing segments

{ "id": "SG1", "label": "Pressing segment", "centerPointId": "C", "carrierPointId": "B",
  "radius": 250, "innerRadius": 214.987, "rollerRadius": 18, "spanDeg": 100, "thickness": 18,
  "startDeg": -140, "originX": 60, "originY": -60, "axisDeg": 0, "side": 1,
  "surfaceLength": 420, "showRack": true, "rackPitch": 12 }

radius is the working radius R, innerRadius the guide radius R₁, rollerRadius the roller radius r₁. originX/Y, axisDeg and surfaceLength describe the flat form.

racks — gear racks

// a fixed rack
{ "id": "RK1", "label": "Fixed gear rack",
  "originX": 128.4, "originY": -61.2, "axisDeg": 0,
  "length": 320, "pitch": 8, "fixed": true, "toothSide": -1 }

// a moving rack on a slider
{ "id": "RK2", "label": "Moving gear rack", "pointId": "P3",
  "originX": 128.4, "originY": -61.2, "axisDeg": 0,
  "length": 320, "pitch": 8, "fixed": false, "toothSide": 1 }

Only a moving rack has pointId — the pair that carries it. originX/Y and axisDeg give the midpoint and the inclination. toothSide (1 or −1) is which side of the axis the teeth are drawn on.

slottedLinks — slotted levers

{ "id": "SL1", "label": "Slotted lever", "pointId": "A1",
  "pivotPointId": "P3", "leverPointId": "P4", "leverLinkId": "L2" }

pointId is the block sliding in the slot; pivotPointId is the lever's fixed support; leverPointId and leverLinkId are the lever's far end and the lever link itself.

attachedPoints — points on links

{ "id": "AP1", "pointId": "P5", "linkId": "L2", "from": "a", "distance": 74.17 }

from is which end of the link to measure from ("a" or "b"), distance is the distance along it. A value greater than the link's length puts the point on the extension. The point itself remains an ordinary record in points — this record only ties it to the link.

extraDimensions — added dimensions

{ "id": "ED1", "label": "Dimension 1", "a": "point:O1", "b": "point:P4",
  "axis": "x", "offsetMm": 62 }

{ "id": "ED2", "label": "Angle 2", "kind": "angle",
  "vertex": "point:O1", "a": "point:A1", "b": "point:P4", "offsetMm": 48 }

Reference points are written as keys: point:<id>, slider:<id>:endA, slider:<id>:endB, plus the centre and ends of a rack or of a segment's form. axis is "x", "y" or absent (an aligned dimension). offsetMm is how far the dimension line was pushed out, or the arc radius for an angle.

variables — the variables table

[ { "name": "R", "expr": "55" },
  { "name": "L", "expr": "R*2.9" } ]

groups — structural groups

{ "id": "G1", "label": "Eccentric drive", "kind": "Eccentric drive",
  "pointIds": ["O1","E"], "linkIds": [], "driverIds": ["D1"],
  "sliderIds": [], "eccentricIds": ["EC1"] }

Groups do not affect the calculation — they only build the object tree and let a whole group be deleted in one action.

paramLocks and formulas

"paramLocks": { "link:L1:length": true, "point:O2:x": true },
"formulas":   { "link:L2:length": "R*2.9" }

A dimension key is the object type, its id and the parameter name. These two dictionaries are what store which dimensions are driving and which are bound to formulas. The most common keys:

dimensionOffsets — where dimensions were dragged

"dimensionOffsets": { "link:L1:length": 34.5, "extra:ED1:distance": -60 }

Stores the places you dragged dimension lines to. It has no effect on geometry at all — only on how the drawing looks.

settings — document settings

Project name

The project name, up to 160 characters. It also becomes the mechanism name.

Save current

Writes the active document to the server. Saving under an existing name updates that record.

Refresh

Re-reads the list — useful if you work from two devices.

Open

Loads the project and closes the window.

Delete

Removes the project from the server. You are asked to confirm — it cannot be undone.

Everything works in the demo: every drawing tool, the solver, the animation, the graph window. There are exactly two differences.

If there is no Open the demo button on the sign-in screen, the demo mode is turned off on that installation.

21.1Keys

21.2Mouse

22.1Messages from the construction tools

22.2Messages from the solver

22.3Why a large mechanism takes longer

The cost of a solve grows much faster than the number of points. Here is what that looks like in practice for a full cycle of 360 positions:

So that one oversized mechanism cannot take all the resources, the calculation has ceilings:

• no more than 200 kinematic pairs and 1000 elements in a document;
• no more than 20 seconds for one cycle.

If a limit is exceeded, nothing “hangs” — a readable explanation appears in the status bar. For scale: the largest ready-made example has 13 points, so in ordinary work these limits never get in the way.

The task. A slider-crank drive with a stroke of exactly 200 mm and a crank radius of 60 mm. You need the block's velocity graph and a table in Excel.

23.1Draw it roughly

1. Take Input crank. Click somewhere in the left part of the sheet — that is the support. Click up and to the right, about half a hand away — that is the crank pin. The length does not matter yet.
2. Take Slider group. Click the pair A1 (the crank end), then click to the right at the level of the support — the block goes there, and the guide lies along the line you have just drawn.
3. The status bar should show Residual …e-8 mm. The mechanism has assembled.

23.2Set the exact dimensions

1. Double-click the crank dimension on the drawing. Type 60, tick Fixed (driving) dimension, press OK. The dimension is now boxed — it is driving.
2. Double-click the block's stroke dimension. Type 200, fix it too, OK. The program will fit the connecting-rod length so that the stroke is exactly 200 mm.
3. Select the slider group in the object list and set Axis angle to exactly 0 so the guide lies horizontally.

If a number is refused, read the red text under the field and press Calculate feasible range: the program will tell you between which values it is possible.

23.3Set the motion

1. Select the drive (Input 1) in the object list.
2. Set RPM — say 120.
3. Check Rotation direction and, if needed, Initial angle.

23.4Check the motion

1. Press Play in the animation strip. Watch the mechanism go through a whole revolution without stalls or jumps.
2. Stop and step through the Position list to the extreme positions.
3. If you need to measure from a different pose, stop on it and press Set current position as initial.

23.5Read the result

1. Analysis tab → Point sub-tab → pick the block in the list. The coordinates, velocity and acceleration at the current frame are right there.
2. Click the Velocity and acceleration chart — the Graphs window opens with those curves already selected.
3. Add other curves from the tree on the left if you need them, and save the diagram with PNG or SVG.

23.6Finish and hand it over

1. Place the dimensions you need with Linear dimension and Angular dimension, and drag them to clear places.
2. Switch to the light theme if the drawing is going to print.
3. Export image → SVG — the drawing for the report.
4. Export Excel — a workbook with tables and charts over the whole revolution.
5. Save mechanism as JSON — the mechanism itself, so you can come back to it.