The in-wheel swerve shifter!

[asid61]

Originally Posted by Tyler2517

Its a really cool idea. I would be really scared of the gears teeth shearing off that close to the final reduction of the drive train.
This may also cause major latency in the drive train something that i don't even know if the shifting could compensate for. Also you could not do on the fly shifting and the complexity of the system is high little lone putting it in the already complex swerve drive. I love the idea tho and think that it may have uses in non drive applications.

Also a RS-540 would work well too, 775's are over kill in my opinion.

Thanks for the input!
The gears are from a GEM planetary and are all 4140 steel IIRC, so I'm not too worried about the stripping.
Due to the wheels not reversing direction every time you shift, the only thing that the CIM has to fight against to accelerate is the inertia of the shafts and gears, not the inertia full robot like in a normal reverse. I did a small test with an unloaded cim and it would reverse instantly, but definitely something to look into. I think/hope the lack of inertia would reduce latency to almost nothing.
Unless you're talking about the sheer number of gears, which I have nothing to compensate for.

The reason I said RS-775 is so that you can turn very very quickly to compensate for not being able to reverse the cims to go backwards. Plus, anywhere you can use a 775 power-wise you can use a CIM (you would have 2 left with this drivetrain), except on a versaplanetary (preferred turning gearbox) which requires modifications.

You can't really do not-on-the-fly shifting technically, because the cim's turning is what keeps it engaged. But in reality you could probably not shift on the fly and be okay.

[Tyler2517]

For latency i meant the time it would take to turn the wheel.

[asid61]

Originally Posted by Tyler2517

For latency i meant the time it would take to turn the wheel.

Yeah, that's something I can't really address. This uses the minimum number of intermediate gears that is possible with this size wheel.

1717 doesn't seem to have problems with their gears, but it's true that the GEM gears have a TON of slop in them. I still can't figure out addendum mods for planetary gearsets, so for now I'll stick with this. Definitely something to work on in the future though.

[Chris is me]

I'm not sure if this would work, but it's an interesting idea. Is there any reason you have only one planet gear? Are the planets going to be carried by anything or are they just floating? Is the planet arm fixed, free spinning?

If you need an initial reduction from the drive motor, why not just shift there?

[Greg Woelki]

I like the idea. My first thought was that this could be better suited to lifts (think 2013 climb) where there has little load when traveling one direction and much more in the other.

[CENTURION]

Wow, that's a really cool idea!

I'll agree with others that it may not be practical for a drivetrain (not being able to shift on the fly, and having to turn the wheels around to go backwards), but I can see this kind of mechanism making it's way into other parts of a robot!

[asid61]

Originally Posted by Chris is me

I'm not sure if this would work, but it's an interesting idea. Is there any reason you have only one planet gear? Are the planets going to be carried by anything or are they just floating? Is the planet arm fixed, free spinning?

If you need an initial reduction from the drive motor, why not just shift there?

There are actually 5 planet gears. The way I CAD stuff, I want to put in all the shafts and e-clips before patterning the planet gears 5 times.

So the reduction comes from the sprockets on the wheel and shaft above the wheel. The cim can go directly above the module right in the center of rotation, to remove the need for gears outside the swerve module.

Why can this not be shifted on the fly? Am I missing something here? Keep in mind that this can ony go forward. There is no reverse because I'm driving sun-ring, not sun-carrier in the planetary gearset. This means that the reverse of direction by the cim will only work against the inertia of the drive shaft, not the whole robot.
Here is a good link to learning about planetary gearset ratios: http://science.howstuffworks.com/tra...ment/gear7.htm
As you can see, the ratio between sun and carrier, which is normally used in planetary gearboxes, is (ring/sun + 1):1. However, this uses a sun and ring mate, for which the ratio is -(ring/sun):1. So when the shaft reverses direction, the wheel continues spinning the same direction that it was before.

[AdamHeard]

If you're willing to give up direction changes (as this drive does), there is a simpler way to get the same affect.

Run two parallel stages of reduction from the motor to module input with different ratios. Put all of the involved pulleys/gears on one way bearings.

When you drive on direction, power will be transmitted through set A while B free spins and vice versa.

Something I thought of that Aren Hill and I have been debating about for a while.

[asid61]

Originally Posted by AdamHeard

If you're willing to give up direction changes (as this drive does), there is a simpler way to get the same affect.

Run two parallel stages of reduction from the motor to module input with different ratios. Put all of the involved pulleys/gears on one way bearings.

When you drive on direction, power will be transmitted through set A while B free spins and vice versa.

Something I thought of that Aren Hill and I have been debating about for a while.

Interesting, and clever! That would be a good way to do it outside of a swerve or wheel, for something like a PTO. However, this way is a lot more compact if you are using it inside a wheel. Outside a wheel though, one-way bearings would do really well.
I always wondered, how do you get the one-way bearings to spin with the shaft though? Wouldn't the shaft just slip? Or do you add screw locker or something?

[Greg Woelki]

Originally Posted by asid61

Interesting, and clever! That would be a good way to do it outside of a swerve or wheel, for something like a PTO. However, this way is a lot more compact if you are using it inside a wheel. Outside a wheel though, one-way bearings would do really well.
I always wondered, how do you get the one-way bearings to spin with the shaft though? Wouldn't the shaft just slip? Or do you add screw locker or something?

Slip inside the bearing you mean? My team used a one way bearing on our winch this year. We press fit it into a bearing block and press fit a coupler into it. The friction was strong enough to hold everything from moving even with 500 in*lbs of torque on the coupler acting against the bearing.

[Madison]

Originally Posted by AdamHeard

If you're willing to give up direction changes (as this drive does), there is a simpler way to get the same affect.

Run two parallel stages of reduction from the motor to module input with different ratios. Put all of the involved pulleys/gears on one way bearings.

When you drive on direction, power will be transmitted through set A while B free spins and vice versa.

Something I thought of that Aren Hill and I have been debating about for a while.

Would you happen to know of a source for one-way bearings that fit in typical FRC drives and are rated for the loads we see?

[asid61]

Originally Posted by Madison

Would you happen to know of a source for one-way bearings that fit in typical FRC drives and are rated for the loads we see?

McMaster has some. You would need to do some load tests though; they're rated pretty low. For that reason they would probably be on the CIM shaft (they come with 8mm bore)

Originally Posted by Greg Woelki

Slip inside the bearing you mean? My team used a one way bearing on our winch this year. We press fit it into a bearing block and press fit a coupler into it. The friction was strong enough to hold everything from moving even with 500 in*lbs of torque on the coupler acting against the bearing.

Wow, that's pretty buff!

[AdamHeard]

Originally Posted by Madison

Would you happen to know of a source for one-way bearings that fit in typical FRC drives and are rated for the loads we see?

I would run 2489K23 on the CIM and 2489K5 on the module input.

Both have quite comfortable FOS as a CIM stalls at ~ 1.7 ft-lbs.

[Jared]

This looks really cool. It looks like it could work well on a 2013 climber, where you'd want to deploy quickly, but raise the robot with lots of torque.

What happens if you're going slowly and somebody pushes your robot from behind? Instead of the wheels driving the motor to go faster, the dog will back out, but it won't engage with the other side because it's going the wrong way, so the dog will be bouncing off the two sides until you speed up the motor or reverse direction.

[Chris is me]

Originally Posted by asid61

Why can this not be shifted on the fly? Am I missing something here? Keep in mind that this can ony go forward. There is no reverse because I'm driving sun-ring, not sun-carrier in the planetary gearset. This means that the reverse of direction by the cim will only work against the inertia of the drive shaft, not the whole robot.

It can't shift on the fly because even if the output direction doesn't change, reversing the CIM will still slow the drive down to zero and then go back up to speed. The motor has to fight the inertia of the drive system when reversing input direction, and this takes time at which point you aren't moving.