pic: Ratchety Swerve Progress

Generally speaking there’s a chain/sprocket or gear stage on one side of the wheel and the bevel gears are on the opposite side of the wheel, and this appears to be the case in your module as well.
If that’s true, you could just stick a cut-away ratchet wrench on the other side of the wheel to not add space compared to a Revolution module. Heck, you could even make a verashub-style ratchet and put it on a Revolution module.

I’m sure this was discussed in a thread prior to this, but what thought process is yeilding the conclusion that ratcheting wheels are a net positive over conventional “both-way” wheels?

No backdriving, so no current draw to play defense if you orient your wheels against them. If you use a 775pro or even an RS-550 to rotate your modules then the loss of the ability to flip the motor direction becomes less important.

Couldn’t you achieve the same effect by rotating the modules such that the wheels are perpendicular to direction you’re defending?

ding ding ding

It appears we have an individual with a solution in search of a problem, that hasn’t found the problem yet.

There are other fun things to try with swerve, making it only spin one way is just detracting from the capabilities, not adding.

I admire the enthusiasm, but it seems you’re a bit misdirected right now, perhaps you could start with a more “standard” swerve to nail down your favorite way to deal with some of the problems? (bearing support, steering motor reduction, hex axle? keys? etc)

I’m still plugging away on new stuff myself.


The ratchet-hub was an idea. May pursue it after ratchety swerve.

Not if you want to push anyone.

But as long as the motor is directly geared to the wheels, the ratchets only help when you’re losing the pushing battle anyway. Other than giving the motors a chance to cool for a later run, they don’t give any benefit to gaining more ground.

Note the “as long as”. Have you considered using a “hammer drill” type system in conjunction with the ratchet? In that case, the ratchet would help you hold ground while spinning the hammer up. It would be tough on parts, and require good traction control, but it might kick the ratchet up from a failsafe to an advantage.

Then you need to rotate your wheels to the correct orientation every time you slam a robot head-on. IMO it’s a lot easier to just stick a ratchet wrench on a shaft and not worry about it at all; the only way you can be pushed with this module is the way you want to go.

+1 to hammer drill; that more than anything else would turn this into a cool option. It’s easy to put a ratchet into a swerve module, but a lot harder to increase pushing power like that.

I’m confused as to how this would work… Could you please explain?

Something that will kick your ratchet forwards one(or many) tick(s) at a time gaining ground on the opponent without giving up any. Essentially you would be releasing more energy then is being pushed against you for a small interval of time to gain some ground. Then you can rest until you release another burst of energy lurching forwards another ratchet tick(s).

I am not great with words but I hope that helps. I like the idea. But I think it’s a bit much for most FRC games. Fun to theorize about however. :slight_smile:

But how would it kick the ratchet forwards?

My domain is software, but an inverted ratchet on the shaft sprung back in the free direction and then a cam that builds up some varying amount of tension released down on to the ratchet might work? Is your question more about how to “build up the energy and then release it” or is it more “how to turn the shaft by hitting it”? This is likely something you would want to somehow shift in and out of.

Other are probably better suited to the task of explaining this. Again, super over complicated for an FRC game.(Or maybe I am just making it complicated because I don’t know better.) Could be a fun project none the less.

Both :stuck_out_tongue: I’ve never heard of this concept until today, and research is getting me nowhere.

Hmmm, I would start by looking at cam’s. Many teams in 2014 used catapults, and for charging the catapult some teams may have used a cam. It’s the same idea as this. Essentially a mechanism that will store potential energy over a period of time. Because of the ratchet we can store more energy over the longer period of time it allows us. Then once the cam reaches it’s release point, all that energy is released, which ends up becoming more work than is being used against us. We then overpower them for a large enough period of time to move in to the next ratchet step. So you are looking for a mechanism that will store energy over time and release it all at once vs the constant output of energy.

Now that I think about it, you want to be looking at the 2010 game. A lot of those soccer ball kickers did close to exactly what you are looking for. Except instead of hitting a ball. You would be hitting something to turn your shaft. I cannot think of an elegant solution for this off the top of my head. But that is a direction for your research.

PS: In FRC, if you want to overpower someone just pick a lower gear ratio and better treads. Before you get to a situation where you would want to think of something like this, traction would probably give out and it would mean nothing.

I’ve never taken apart a hammer drill, so I don’t know how actual ones work. The bottom line is that the high speed motor builds up momentum in a freely rotating “hammer” then quickly engages it with the load to push it forward. The ratchet prevents backdrive while you spin up for the next one.

The archetype (linear not rotational) is hammering in a nail. You’d need a massive lever to push a nail into a piece of wood, but by swinging a hammer and making it collide with the nail, you can make a good bit of progress each swing. In this case, the ratchet is in the form of grooves on the nail which engage the wood and keep the nail from falling back out.

My “never done anything like this” first guess at the mechanism would be some sort of centrifugally controlled clutch that engages when the input “hammer” reaches a given speed, and disengages when the input shaft is stopped or reduced to something much slower than the engagement speed. This way, the clutch would remain engaged for normal driving and light pushing, and only go into “hammer mode” when the going gets tough. [Edit: as a positive side effect, this would probably reduce total inrush current when starting the robot from a dead start.]

Googling or Binging “electric hammer drill” gives plenty of COTS examples; I’m sure exploded diagrams of the mechanism for some are available in the form of a parts list.

So could this go into the drive gearbox? I’m thinking a steel flywheel that has a “spinup” state and an “engaged” state where it is removed from it’s motor input and put into the drive output, sending an absolute crapload of KE to the drive wheels.

I’m still having difficulty following this logic. In the end, aren’t you limited by the static frictional constant of the tread on the wheel and the carpet? The ratcheting wheel ensures your wheels will not back drive, but that has no bearing on if you can or cannot be pushed around. I’m also confused by the notion that defense is all about slamming robots around or engaging in prolonged pushing matches. In my experience, this kind of defense is far from ideal.

If you’re the one playing defense, then you want to approach from the side and get in front of them normally. In a swerve drive that could mean leaving your wheels facing them, so you would need to be actively pushing against them in order to stay in place/defend. If you’re running a 4- or 8-775pro drive, that’s the kind of condition you want to avoid if you’re running a 16fps+ drivetrain to avoid both stall and brownout conditions.
115 actually browned out and caused a roboRIO reset instantly at SVR. 254 steamrolled them behind the airship and the pushing with a drivebase geared for 21fps on 4 CIMs browned them out and dropped the voltage to the reset threshold within a fraction of a second. With a ratcheting drivetrain, you can gear high and not worry about being pushed around in a bad case.

All that being said- I don’t really think ratcheting drive is all that much of an advantage. The disadvantages can be few if you design it right, however.