pic: Ladies and Gentleman, We Have a Drive Gearbox



Just a little progress report on the 10-wheel ratcheting swerve (insanity drive?).

Some specs:
-6 CIMS
-4.66:1 gear reduction
-Weighs a little over 12lbs

By having a single drive transmission, you’re not making a swerve, but a crab.

Follow on question: What do you mean by “ratcheting?”

Each steering module is going to have a ratcheting drive wheel :yikes: (thanks Jaci!). Also, I thought independent steering is what turns crab into swerve?

reminds me so much of

There was some possible inspiration from chainzilla :stuck_out_tongue:

Can you elaborate on what you mean by a ratcheting drive wheel? And why? And the designation between swerve and crab is quite blurry, but I think you need independent steering AND independent power for each wheel for it to be considered a true swerve. Even if you have independent steering, there are still maneuvers you cannot perform: most notably driving in a straight line while rotating.

This is the separation. A swerve decouples robot orientation from heading. It allows one to rotate while traversing the field.

A crab doesn’t allow these motions.

Maybe wheel wasn’t the word I was looking for. There is going to be a ratchet attatched to every drive shaft, that way the drive shafts can only rotate in one direction and lock when you try to rotate them the other way (useful in a pushing match?). The ratcheting is really just to add some more challenge to the design. Maybe continue this conversation via PM?

I’m most curious about what the objectives were going into this design. What points are you looking to accomplish? What are the design constraints and why?

It’s tough for us outsiders to understand what is going on and the reasoning behind design choices without first knowing what you set out to do.

Would it be? The typical concern in a pushing match is wheels slipping, not turning backwards (that’s what motors are for).

So you’d need to steer your wheels 180deg to go backwards? Just remember that one of the few performance downsides of swerve as a holonomic drivetrain is the lag time for the wheels to align the way you want to drive. Limiting yourself to steering just a single forward vector will basically double this time for general play.

This is meant to be a CAD excersize that could also be transferred to use in combat robotics/FRC if anyone wanted to. The ratcheting functionality is there to resist pushing without stalling motors, which is something I think would be very useful. I’m looking to gain experience developing my own steering modules and gearboxes. The only constraint right now is to keep it under 60lbs because that seems to be about the maximum weight anyone would ever think of putting into a drivetrain. If you can think of some other constraints, that would be groovy :slight_smile:

Do you have a closeup of the ratchet mechanism? I’m having trouble picturing how it would allow you not to traction-limit the drive in a pushing match. If your goal was to stay still (say you’re shooting or something), that’s one thing, but if you’re actually in a pushing match trying to move through someone, it’d seem like your motors would always be trying to bear that load “in front” of the last ratchet tooth. Is that within the design specs in some other way?

What made the ratchet more appealing for this situation (especially with steerable wheels) than a shifter?

I want to use something similar to the ratchet in this: https://www.chiefdelphi.com/forums/showthread.php?t=156415

It’s benefit in a pushing match would come from being able to rotate half of the drive wheels to ratchet one way, and the other half to ratchet the other way. That way you have 5 wheels that are locked and 5 wheels that can still push against the other robot. This would also prove advantageous in that you can “rest” half of your drive motors during a pushing match, switching halves every so often so as to not burn out any CIMs.

So the wheels that are not being driven at any given time resist the wheels that are?

Surprise! It’s a one robot pushing match!

Worth noting that with independent steering you can steer the wheels diagonal to each other (like you would with omniwheels), and any robot trying to push you is essentially trying to push you sideways.

Yeah, this is how we’ve always done it. Even trying to rotate us by a corner is basically impossible in the “freeze” mode (1640). But I guess given some set of (theoretical at this point) inline and transverse coefficients, the ratchet situation might yield similar results. (Though I’m still struggling to understand the additional benefit for the extra effort and issues.)

It sounds like they’d also be “robbing” normal force from the driven wheels, no? So the actual forward force would be basically half of the status quo case?

Just to clarify here, if you’re using this in FRC, having 6 drive power motors and 10 steering motors uses all available PDP slots.

Add a passive gear slot and PTO climber and you’d be ok for STEAMWorks though!

Not at any given time, only in a pushing match. If you switch it out of 50/50 orientation (that’s what I’m calling it), all wheels are rotating the same way and will not resist each other.

5 steering motors, opposide steering modules will be linked. Guess it is a crab drive :wink: