Compact Shifter for Mecanum Drive

I saw 10D’s shifting two-speed transmission (which is a very nice way to build a shifter, by the way) and I thought:

  1. How can it use less axles?
  2. How can it use less gear-to-gear power transfer?
  3. How could it work for Mecanum drive shifting?
  4. How could I make it more compact?

So here are the changes I wanted to make:

  1. Only 1 extra shaft between the motors and the wheels.
  2. Only 1 extra gear-gear meshing point.
  3. Shift two inputs into two outputs with one pneumatic cylinder.
  4. Run the cylinder parallel to the drivetrain so it doesn’t take up space on the interior of the robot.

*One disadvantage I found I would just have to deal with:
The axle will have to stick out of the outer side of the drive base ~3/4", but if your intake is 18" wide you would want that extra room anyway for the arms of your intake.

Before you look at the pictures (is it too late?):
The upper shafts would be powered.
The pictures depict high-torque mode.
Imagine the omni wheels were Mecanum wheels.

And here’s the result:
[right-side C-channel is hidden for better viewing]
[right-side C-channel is hidden for better viewing]
[how it would look with the C-channel]

CAD and rendering done in Autodesk Inventor.
Some inspiration from CAKE’s transmission.

The actual attachment between the rod end and the shifting arm is not shown, but it would just be 1x4 bars extending from the vertical faces of the angle gussets to surround the two nuts on the piston.

Basically how it works:
The pneumatic cylinder fires to rotate the shifting arm (image 2).
The shifting arm, by rotating, pulls out one axle and pushes in the other.
The output gears (secured to the axle by collars) are then shifted to mesh with their respective input gears (powered by the motors).
The sprockets on the output shafts slide along the axle so they stay in the same location relative to the wheels/drive base frame so that the chain does not slip off. If you’ve ever ridden a bicycle and tried to shift so the chain rides on the smallest sprockets on both front and back, you know what I mean (the chain falls off).

It’s kind of hard to see exactly what gears mesh with what other gears on the renders, so if you would like another view, just ask and I’ll throw up another render.

In the picture it shows there are two wheels. You said that just teplace the omni whrels with mecanum. How would this transmission work if it seems that this whole base is connected to both wheels.

The thing I didn’t understand right away was that there are two separate gearboxes in this picture, they’re just controlled by the one piston. For each set of gears, the high strength pair is for the high torque mode and the ordinary pair is for the high speed mode. Once you understand that it becomes more clear.

Nice work and good explanations!

Yes, there are effectively two shifters, which are isolated from each other, except by the shifting arm, which shifts both the front and back wheels with one motion. The front and back wheels are controlled by their own motors and their own drivetrain.

Wow this is a really cool transmission concept. If my team wasn’t using 4 pistons already we would look into this for our robot. I will definitely keep this in mind though. I really like this transmission.

Has this been constructed yet? I would love to see it in action.


I might be able to build it in a week, but probably not. All I’ve got now is the computer. If someone wants to build it and has parts, I can help with any of the finer points of construction.

will each of the sprockets have chain leading to the wheels? and if so, when the transmission shifts will that not mis-align the chain?

I would really like to build it myself (I am quite capable) but our team needs to focus on the new game right now. If we don’t end up with a pneumatic arm then we will take this transmission into great consideration, (We are having Mecanum drive no matter what.) but for now we do not have time to build “for fun” projects.

If someone does get around to building this please post video/pictures. I would really like to see this in action.

You have a whole year to build robots for the game, though. Now’s the time for fun projects :slight_smile:

Yes, but no. The sprockets will slide on the axles when the axles shift. The sprockets are held in place by straps (not shown) that run on either side of the sprocket and are attached to the C-channel on the drive base. Make sure you use those nice, new shiny axles (the really smooth ones), when you build this. You could also do what 10D did with the gear that meshes with a very long gear, so that it is always in contact, but then you need one more axle in the drivetrain.

In order to make the sprocket slide better, I’m thinking that it would be best to sand the axle just a slight amount. Adding some lubricant could also help significantly, I’ll go ahead and test that later today.

Yes I think that would help greatly.

In order to make shifting smoother, I would do these things:

  1. Sand down the edges of the gear teeth.
  2. Match the output gear speed to the input gear speed (using encoders).
  3. Make sure there is enough space for the input to fully disengage from the output so matching the speeds is actually possible.