Question About Gear Boxes

Hello my name is Chris Evans I am head of drivetrain, along with frame & structure for Team 1783 The Firebots. Recently I have designed a three speed gear box, and I need a little bit of help as far as how to make the transmission shift, and what to use as far as gears? Any help with this would be greatly appreciated.
Chris Evans a.k.a. Mexican

I have only ever seen 2 speed gear boxes, is there a reason a 2 speed wont work?

Check the whitepapers section and search the forum for information on gearboxes. I’m especially fond of the 222 ball lock shifter :wink: .


Welcome to the technical world of CD. You should be able to find more information than you know what to do with here. Just be sure to search before you ask…

Now, I find it ironic that you’ve been able to design a 3-speed transmission, but don’t know what gears are in it or how it shifts. Maybe you could elaborate a bit on your preliminary design, how you came about this design, etc… If you have any sketches, feel free to post them here. As Cliff pointed out, there are a few two and three speed designs listed in the whitepapers section.

I think we’ll need more details before we can help you with your design.


You forgot the four-speed. :wink:

Historically, transmissions have been shifted one of three ways:

  1. Pneumatic cylinders. These are relatively cheap, easy to install in most cases, and they have enough oomph to them to get the gears shifted. Problem is, that requires a pneumatics system, which adds both weight and complexity to the robot.

  2. Servos. Servos are cheaper still, can be put in a middle position (good for shifting the DeWalt three-speed transmissions) and don’t require any added systems, but they sometimes don’t have enough force to do the job. And your programmer will have to do some fiddling to find the right value to use for each gear.

  3. Motors. Teams will use a kit motor (the Globe motor seems to be a common choice) to turn a rod to shift the gears. This is sometimes preferable over pneumatics, but they may be a little slower to shift, and you have to add feedback of some other sort (encoders, switches, etc.) to make sure the motor’s keeping the robot in gear. Of the three, this is generally the least common in my experience.

Each has their highs and lows, which only you can evaluate as it pertains to your design. Hope it helps!

It would certainly be helpful if you could describe in a little more detail what kind of gearbox you designed. There are several methods to shifting. Most FIRST transmissions are either mesh or dog shifting mechanisms (search around the forums and whitepapers for more detailed descriptions), but there have also been ball and pin shifters that a few teams have used. I suggest surfing around the forums a bit more, and perhaps even communicating with some individual teams. You may want to investigate Team 33’s 2004 4-speed mesh shifter, 45’s dog shifters (or its cousins the AndyMark shifter and AndyMark servo shifter), 222’s ball shifter, 254’s (or the many teams who have adopted variants of its drive) pin shifter, or the DeWalt transmissions used by many teams (such as 469).