Team Unlimited's Two Speed Transmission

This shifter was used in Team Unlimited’s 2006-2007 robot in the FVC (now FTC) program. This shifter worked amazing, only failing once in 4 tournaments and won multiple awards.

Here are some renders from Maya:

And there are many more. If you are interested in this design you can PM me here, or you check out our website at:

If you only want to read about the gear shifter we made a page that is just about it:
And some prototype pictures can be found here: [

I hope you all enjoy this shifter :smiley:


How did you clean the edges of the gears after you beveled them?

Wow great idea! good work

My team placed a metal file in a vice, and then attached a gear onto a power drill. This got the bevel. To clean the gears, we took a small/fine file and ran it through each gear tooth to remove excess. I also recommendvsanding cord, it works wonders to clean the inside of the gears. I hope this helps.

once i saw your idea on chief delphi i tried to imitate it. although i didnt follow the picture exactly, using just one servo to shift was a great idea.

We actually used a motor, the servo seemed to not have enough torque when we used it, and when we geared the servo down to get the torque, there was only about 40 degrees of movement, so we used a motor w/ the gear reduction.

Anyone ever tried this with 12 and 36 tooth gears? I am building a tank and to keep the size down and also its easier to build I want to use 12 and 36 gears. Anyone had problems with this? Also did you bolt the end gears together?

I have not tried this gear shifter with anything but a 5:3 and 3:5. This summer I am going to test out different ratios possibly. My only concern with the 12 tooth gear is that when it is beveled too much force will be on the gear and it will be very prone to snapping.

That sounds like a job for the heavy duty gear kit!

The metal 12 tooth gear is coming soon so this wont be a problem.


ive always wanted to make a gear shifter…summer project!

god i love summer :smiley: cant wait!

It is a nice compact gear shifter. We actually made one that was small enough to fit into a square bot, but we had to trim the end metal as the gear train was like .5" too long.

Our latest gear shifter is like this:

It is built.

Very nice, but clutches seem to be missing… this might not be good for the robot. If you make a programming error and make the 3 motors on one side go agains’t each other, than the motor’s will be done for.


No not really. Also every motor from picture is one from this picture.

Also we find that the clutches throw the balance of the drive shafts off. I think it will be ok. If not you can see the pile of replacement gears we have.

Did you bevel any of the gears?

As far as not useing clutches can you explain what you mean by “throw the balance of the drive shafts off”. We have developed a policy of using clutchs when we can however when we don’t have space for some reason we don’t. There is plenty of space in your design so I’d like to understand your reasoning.

Even though you have extra gears, why go thruogh the trouble of changing them when you can just put on a clutch. Throwing off balance… not sure what that means?


If you look at a clutch it sometimes does not sit level in the motor making the drive shafts wobble. This increases bearing loads and also makes it hard on motors internal gears. Is this better then no clutch at all? Well I am not sure.

But if you can see in picture I am not using any bearing blocks on the side were the motors are mounted meaning so the motor is supporting shaft. It it say the drive shaft wobbles it would make the gears mesh funny which would increase friction.

I do always place clutches on our real robots but I feel they were not needed as much on this one. Also I have never had a clutch save a motor.

Yes the gears are beveled.

I pretty much never use the clutches. Since you can stall and even back-drive a motor through a clutch, it seems to me their trip-point is too high. I guess it would save a motor if something were trying to back-drive it really fast, but that would be a pretty rare occurrence.

I find that the slop they add is not worth the peace of mind they bring, but then I’ve not fielded a competition robot yet. I have started designing my clutch-less bots with motors that are easy to unmount when practical, just in case…


  • Dean

In competition I think it’s a good idea to use clutches. You just never what is going to happen, a major component breaks and you end up having to ram and play defence on other bots, or another bot plays defence on you. Syntax Error and Mainframe Meltdown have only broken one motor over the 4+ years we have been teams. I think we haved saved 10+ motors because of the clutches.