Modelling and Assembly of Gearbox. Assembly of imported (Parasolid) parts models. 

Tamiya Gearbox


Gearbox Comparison

Typical operating voltage 3 V3 V
Gear ratio options 12.7:1, 38:1, 115:1, and 344:158:1, 203:1
Free-run motor shaft speed @ 3V 12300 rpm12300 rpm
Free-run current @ 3V 150 mA150 mA
Stall current @ 3V 2100 mA2100 mA
Motor shaft stall torque @ 3V 0.5 oz·in0.5 oz·in
Data from
Motor Specification Sheet

Tamiya Twin Gearbox: Centre

Let's start with the gearbox centre (it's a bit easier than the sides).

Watch out for symmetry here - you can save yourself some serious time. The perfect left/right symmetry means you should build exactly half the part and mirror at the end. In other words, build one side and then do a final mirror.

We start with a new technique here. Inserting an Autocad drawing into Inventor as a sketch. We then use this sketch multiple times to build separate protrusions on the 3D model.

Autocad sketch. Download: gearbox-centre-view1-tl.dwg (42kB).

This will be used to build the centre geometry.

Main Drawing for Gearbox Centre

Tamiya Twin Gearbox Centre. PDF drawing version: gearbox-centre.pdf

Gearbox Centre Videos

This video shows one way to begin the model;

  • How to import an Autocad drawing into Inventor model.
  • How to build multiple protrusions from a single sketch (shared sketch).
gearbox-centre-part1b.htm: (Autocad *.dwg to Inventor *.ipt) 5:28 min 20130529 19MB
gearbox-centre-part2.htm: (Shared sketch, mirror feature) 6:30 min 20130516 10MB

To complete the part, do a body mirror to give this...


Tamiya Twin Gearbox: Left Side

A drawing for the left side of the gearbox is shown below. "Gearbox Left Side"

Study the drawing and decide how you should begin. Always keep your eyes out for a suitable place to place the reference planes - like an axis of symmetry, or a major centreline/plane/etc. This part has some symmetry, but more importantly, a lot of the geometry must match with the Gearbox Centre. Outside edges have a general fillet radius of R0.5, which is best applied very last.

Start with the same reference sketch as we used on the Gearbox Centre.

Download: gearbox-centre-view1-tl.dwg (42kB).

Using the same Autocad drawing saves time, but also ensures the parts will match together.

Tamiya Twin Gearbox Centre. PDF drawing version: gearbox-twin-side-TL.pdf

Gearbox Side Videos

This video shows one way to build the side;

  • Start with the imported an Autocad drawing (same as Gearbox Centre).
  • Careful use of feature-mirror.
  • Apply general fillets as last step. (Avoids fillets in sketches, and allows simple model during construction)
gearbox-left-01.htm: (Autocad *.dwg to Inventor *.ipt, Boolean) 4:52min 20130524 11MB
side-02.htm: (Shared sketch, mirror) 16:48min 20130524 45MB

That should do most of the tricky bits.

The rest is straight forward (Feature step-thru only), which is another way of saying "work it out yourself..."

side-03.htm: (Feature Step-thru only) 4:11min 20130524 12MB



Legacy (Old Drawings).

Old Gearbox Centre

For students who started the model on the previous (old drawing). The newer drawing has simplified geometry.

Old Gearbox Left

Note. This drawings has some errors - and will not line up exactly with the new Gearbox Centre. There is also a deliberate error that will be apparent when the parts are assembled together.

Larger Image (1186 x 885 px)  gearbox_left.gif

There were a few dimensions missing, so here is some more detail (below)...

Construction Hints for the Left Side using Edit in Assembly Mode

Note: Edit in assembly mode is an important skill in using CAD. In a real design situation we don't know the design of a part before we assemble them, we build the parts IN the assembly. Here's how to do it.

Making the Right Side

Making a mirrored version of an existing part

Note: (The name Left.ipt and Right.ipt are only example names. You can call them anything you like)

The Bad Method

A brute force way of making the right side; (In Left.ipt > mirror part > cut the left side off > save the remaining as Right.ipt)

It seems to work, but it is BAD. Why? Because if you modify Left.ipt, there are no automatic mods done to Right.ipt.


The Proper Method

Insert a copy of Left.ipt as a mirrored part and then save as Right.ipt.


To do this in Inventor;

New Standard(mm).ipt > Get out of sketch mode (Finish sketch) > Manage Tab > Derive > Find your part...

The next dialogue allows scaling and mirror. In our case sclae is 1:1, and we mirrored across the XZ plane. You might use another plane...

Press OK and you have a mirrored part. Don't forget to save as a new name!

Gearbox Assembly

Centre, Right Side, Left Side, Motors (L&R), wheels and axles (L&R)

Attach Wheels and Tyres imported as Parasolid files.

Download Zipped File: Download all the parts as a zipped file: wheel  (45kB)
Click on the link above and SAVE the Parasolid files somewhere sensible. (You may have to right-click > save target as...)
Now unzip the file. (Double-click, Extract all files...)

    How to Open Parasolid Files Using Inventor.
  1. Open Inventor after you have extracted the zip file
  2. Open > Files of Type... Select Parasolid Text Files (*.x_t) >
  3. Now you should see the parasolid files listed (assuming you have extracted the zip of course)
  4. Open each one and save as Inventor *.ipt format
  5. Now you can assemble these parts as usual.

The Axle

There is an AXLE that runs from the centre of the gearbox to the bottom of the hexagonal hole in the hub. It is 50mm long with a 1.5mm chamfer on each end. What is the cross-section of this hexagonal rod? You can get this information from the existing wheel_hub.x_t that you downloaded.

Unfortunately, the Parasolid format wipes the Browser-Bar history - so you can't go in and steal the hexagonal profile sketch.

Two ways to make the axle:

1. Create in-place. Create the axle in the assembly: Build the axle from the bottom face of the hub, use  "include" to make the hexagonal profile, then protrude it 50mm. Once the part is saved, open in part mode. Now cut the chamfer (1.5mm x 30 degrees) on each end using "revolved cut". Now go back to assembly mode and finish off the assembly constraints (mate, align etc. The chamfer will help you when using "axial align").

2. Steal the sketch. Open the wheel hub (the centre part that the axle fits into) Pretend to draw a sketch on the hexagonal face, but while in sketch mode copy the hexagonal face onto the clipboard. Open a new part and paste this skectch, extrude 50mm... etc

Assemble these parts together as a sub-assembly, and then assemble this subassembly (twice) into the gearbox.

Done!   (No, you do not have to draw all the gears inside, but you can if you want... )


  • All parts are properly constrained (locked)
  • The Gearbox Centre is the first (grounded) part.
  • Wheels must spin with the axle

Completed Gearbox/Wheel Assembly

Relevant pages in MDME
Web Links
  • Google search:
  • INVENTOR tutorial. Refer to: Assemblies