Ratcheting transmission

Ive been thinking of an idea for a drive transmission that would be only a 2 motor v5 drive but have 2 speeds. Basically it would have 2 different ratcheting systems per side so that the high torque ratio will lock on the output shaft but be able to slip on the input shaft. Then the high speed ratio would lock on the input shaft but slip on the output. i’m not sure if that would work but more or less the concept is to have the high torque be in use until the robot is moving fast enough for the high speed ratchet to not slip. Would this work?


If you need more torque for what your doing yeah it makes sense but otherwise just slow the motors down but it would be awesome for zooming around the feild then slowing down, big time saver.

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I would just be careful with having a ratchet on your drive. If they aren’t built to slip well they will really slow down your drive.

what would be the best way to make a ratchet that could slip well, would it be with pillow bearing or like a shaft collar with a screw on it?

I honestly wouldn’t know. I had a low strength ratchet system (wouldn’t be great for a drive transmission)which used a pillow bearing. It slipped fine but with all the other things (chains etc.) I had connected to it there was just too much friction.

I could remake it if you wanted it, but it probably wont be the best choice.

I saw that some teams used screws and shaft collars as the ratchet which i’m going to try tomorrow. I think i can get it to work in one direction but i don’t know if the system would work in reverse for going backwards tho.

we used a keps nut on a standoff for our worlds robot indexer and i worked 99.99% of the time

Check out 315G’s post-worlds breakdown video for some excellent use of ratchets.

Would you be able to elaborate a little more as to how this will work? Let’s say you want to push someone across the field — if you’re at a low speed but apply full power to the joysticks, will it be on low-torque or high-torque mode?

From what I understand of this it would only work moving forward and you wouldn’t be able to move backward. But if the motors are spinning in one direction it would be fast and the opposite direction it would have more torque. So I wouldn’t recommend doing this but one thing you could do is use ratchets to make it fast when moving forward but have more torque when moving backward.

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Well more or less how I’m thinking is it will try to move as fast as it can forwards, so if its pushing something the high speed will ratchet and the torque will lock but when the robots moving faster enough the high speed gets enough grip. I’m not sure how its gonna work backwards yet.

@inspiron108, I believe, the best you can do with ratchets is what @James6555 said: high speed moving in one direction and high torque moving in another direction.

Also, were you planning to use two motors per side or two motors total - one for the left and one for the right side?

If two motors total, then having an option to choose between high speed and high torque going in either direction is not possible without an additional motor or pneumatic piston to shift between modes.

You will need additional motor one way or another. If you want to learn more theory about shifting and non-shifting transmission, here is the link to the thread from 2016:

In that thread I have linked multiple examples of the transmission designs as well as the theory why popular planetary or friction based two speed transmissions could not work without locking or shifting (high output resistance will backdrive weaker power input).

It also has an example of working two speed transmission that uses worm gear that, if you think about it, would be equivalent to the two way ratchet functionality. However, it wasn’t very practical because worm and worm gear have a lot of friction losses and are not easy to build with.

So, you are thinking in the right direction about using ratchets to help transmission not to backdrive one of the inputs under high loads, but there are limitations which may be too much of the inconvenience for the regular gameplay. Such drivetrain may be only compatible with very specific game strategy, where you need to drive fast only in one direction.

That would require much more complex mechanism similar to the Centrifugal Clutch. You, probably, don’t want to go that way. But if you try, we will be thrilled to see the results.

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