# Utilizing pre-made gears in a gearbox

I’m starting to design a gearbox in Inventor, and I guess I’ve run into a problem. Instead of using the design accelerator to make the gears, I would prefer to use gears that already exist that would be difficult to create on my own (such as dog gears or spoked gears). Is it possible to take pre-existing gear models and constrain them together like the ones output by the design accelerator (i.e with movement constraints)? If that’s not possible, how would I go about properly distancing gears from one another to at least make it appear right?

There are gear models available on Vex pro’s website. They have a wide variety of gears to choose from.

There are motions constraint available for use in inventor. I don’t remember exactly how to use it, but I think its in the same constraint window that you would use for a mate or flush constraint.

You can use a gear distance calculator to get the distance between gears right. They are all over the place online.

Hope this helps, let me know if you have any other questions!

For finding the distance between the centers of two meshing gears (in inches), you can use the following formula:

(T1 + T2) / (2*Dp) + C

Where:

• T1 is the number of teeth on the first gear
• T2 is the number of teeth on the second gear
• Dp would be the diametrical pitch of the gear (Most of the AndyMark and Vexpro gears have a Dp of 20, which means that the diameter of a gear with 20 teeth is 1". Some have a Dp of 32. You can buy all kinds of neat sizes from other manufacturers)
• C is an additional offset to make up for manufacturing tolerances. If everything could be made perfectly, then C would be 0. In real life, the hole isn’t exactly in the center of the gear, the two bearing shafts aren’t the exact right distance apart, etc. Most AndyMark products use a value of 0.002" or 0.003" for this offset. You can download some gearbox models and measure the distance from one bearing to the next to see this.

Thank you both so much!

Thank you very much I figured it out. Its the motion tab in the constraint window. Select roataion for the type, forward for the solution, and T1/T2 for the ratio. I just had to make sure the teeth weren’t occupying the same space before I did that.

This works perfectly. Thanks!