The in-wheel swerve shifter!
 

So I made an autoshifter in CAD using a weird custom dog, parts from the GEM gearbox (ring gear is a measely $10 vs. $100 for other internal gears) modified for this purpose, and a custom wheel made to fit the ring gear.

The way this works:

0. There is a primary reduction from CIM to wheel shaft.
1. The shaft is spinning in one direction, say, clockwise. The dog is keyed to the drive shaft and spins with the shaft. It also engages with the hub of the wheel, to direct drive the wheel from the shaft. The dog is "locked" to the wheel due to the acute angle of the teeth. The wheel spins clockwise with the shaft.

2. There is a collision with another robot and the robot gets into a pushing match. The driver flips and switch, and the CIM then reverses direction- now the wheel shaft spins counterclockwise.

3. The dog spins with the shaft. However, now the dog is no longer "locked" in place due to the shape of the teeth. Now, the obtuse-sloped side of the tooth contact the like side of the wheel hub and pushed the dog into engagement with the sun gear of the planetary gearset.

4. The dog "locks" into place with the sun gear due to the acute angle of the teeth. The sun gear spins the planet gears which transfer power to the ring gear. Due to the nature of planetary gearsets, a counterclockwise rotation of the sun gear with the planet carrier locked produces clockwise rotation of the ring gear. This means that the ring gear, which is locked to the wheel, now spins clockwise. Thus, the wheel still spins clockwise after the shift.

Essentially, all you need to do in order to shift is the reverse the direction the CIM is spinning in.

Obviously, this poses the problem: how do you go backwards if you reverse the CIM to shift and the wheel only goes forward?
The answer: you can't. This is only suitable for swerve drives for this very reason. You have to turn the wheel to go backwards. RS-775 18v are suggested for turning motors.

In order to manufacture the parts in the CAD, you would absolutely need at least a 4-axis CNC due to the weird dog and mating gear/ hub. Not to mention the wheel itself. Because my team lacks the resources to do this, I decided it would be fine to release my CAD of this.

There's probably a ton of errors in the CAD right now (I've only cadded a few of these, and this is the first actual possible swerve module with it) but I wanted to see what the CD community thought of this idea quickly. The CAD is missing bearings, circlips/ eclips (I use the latter), and a miter gear on the primary shaft. Reduction is accomplished with the sprocket for an adjusted 20.0fps high gear and 7.5fps low gear. This is can go down to something like 18fps high gear pretty easily just by increasing the size of the versasprocket. I only had a 34t versasprocket on hand in CAD, but 38t would be preferred.

I use SolidWorks, so if anybody would like the native SW files I have those on hand for the weird dog geometry.

Files in STEP format for download here in a zip folder: https://drive.google.com/folderview?...&usp=sha ring


EDIT: Forgot to say, feel free to slam this however you feel. Anything at all. I have designed a ton of swerve modules (upwards of 15) but none of them have been built. So any input at all will help with the next ones.

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

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. :P But in reality you could probably not shift on the fly and be okay.

Re: The in-wheel swerve shifter!
 

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

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

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?

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

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!

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

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?

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

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?

Re: The in-wheel swerve shifter!
 

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)

Wow, that's pretty buff!

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

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.

Re: The in-wheel swerve shifter!
 

Like I said, the motor only fights against the drive shaft. That's just a couple miter gears, two 3" shafts, 2 sprockets and a gear. The CIM will instantly reverse unloaded, so even with the above it's not a lot of inertia.
That would be something that would be debugged and found in testing.

Interesting example. If a fast robot pushed you, the dog would instantly lock into the other gear, be it low or high. Then as you said, it would probably bounce around. I would want to test this too to see for myself the ramifications.
You would have to have code to debug this situation, probably with current sensors to see if the current gets too low, signifying a robot is pushing you. Then the cim would reverse direction.
In any case, then you could just shut down the cims if it continues (it would be a pretty obvious strategy) and you're going in the direction you want to anyway, but faster. So that situation would be useless for the other robot.

Re: The in-wheel swerve shifter!
 

Would you then have to put some sort of brake system on your roobt? or would you simply have to spin the wheels the other direction to get them to slow down?

Re: The in-wheel swerve shifter!
 

Why are you ignoring the load of the robot and the drivetrain itself? Even with your shifting coupler, it will only disengage as the motor attempts to turn the shaft the opposite direction. Until this is disengaged, as the motor slows the drivetrain slows, and the load of the drivetrain is placed on the motor.

CIMs do not "instantly" switch direction under zero load. Quickly, maybe, not instantly.

Re: The in-wheel swerve shifter!
 

I share the concerns about the forces seen by the dog teeth; steel or not, the shock loads can easily exceed several tens of LbFt, translating to hundreds of LbF on the tooth.

But that can easily be compensated in the final design. Overall a very ingenious solution!

As for needing a 4-axis CNC: Naah. We got metal files and hordes of Freshmen...

Re: The in-wheel swerve shifter!
 

I want to see an in-wheel CVT/IVT using two motors and a planetary transmission.

Re: The in-wheel swerve shifter!
 

If I'm visualizing this correctly, if you are driving and then stop, the engaged gear will push past the dog gear because of the inertia of the robot and the dog gear will be pushed back and forth as the robot comes to a stop.

Re: The in-wheel swerve shifter!
 

If you took a Sturmey Archer S3X fixed gear 3 speed hub you could make a 3 speed swerve drive. It would most likely be to wide but it would work for testing and as a base for a interesting design. Remove the flanges and mount some tread to the hub and you have a 3 speed wheel. You would want to cut the axils down and a few other things but it would be great for testing concepts and to work from.

Re: The in-wheel swerve shifter!
 

You could certainly test the concept with them like you said, but as far as a competition robot goes they aren't just, wide, they're also two pounds each!

Re: The in-wheel swerve shifter!
 

That is why I said they would be good for testing. Also the design is worth looking at as a start of a possible gear box design. I am not saying use the parts but some of the ideas. Any way this was posted for giving ideas to think about.

Re: The in-wheel swerve shifter!
 

Okay, consider this:
As soon as the cim begins to slow, the mated hub/gear will continue spinning at the previous speed, as it is not mated to the shaft except by the dog (which is slowing down). The obtusely angled faces on the dog and hub/gear will contact each other and push the dog into a mate with the other hub/gear, which is spinning in the opposite direction as the original mated gear/hub.
Keep in mind the cim is accelerating to match the speed of the second gear/hub, so its opposite spin, combined with the cim itself accelerating in the opposite direction, will make the shift time extremely low. The inertia of the robot aids the shift.

I said "instantly" as a hyperbole. It was undetectable by the human eye. The only way I knew it has reversed was because I was holding the cim and I felt it shake.

I still want to test this. Like I said, the inertia aids the shift, so I want to test under load to see if it shifts properly.

Freshmen doing this would be interesting. :D

Funny story, I was just looking into this. They seem really cool, but I'm worried about it shifting when the motors slow down due to the uncontrolled autoshifting on weird turns. I also am not sure what drives the shift. Love those bicycle gear hubs though.

I cadded something like 5 of these for a few weeks before I realized there was no torque advantage to using a planetary IVT. And the only other CVTs I saw were cone CVTs and the like. So I moved onto planetary shifters and swerves.
None of my designs were in-wheel though. That's like... weird...

Well, if you can spare the weight. Swerve chassis that don't shift normally can be extremely light (<30lbs with motors).

Re: The in-wheel swerve shifter!
 

Interesting question; I hadn't considered that.
To slow down...
hm...
when you stopped down the cim, the shifter would shift into the other gear and then stop. Merely slowing it down would cause the angled faces on both sides to push the dog around I think, until the robot decelerated to the speed of the dog? Or does the motor actively force a deceleration by contacting the other mating gear/hub? I need to visualize this.
I need to think on this one. Very insightful of you.

Re: The in-wheel swerve shifter!
 

You can see shifting at just past 2:01.
http://www.youtube.com/watch?v=7LTZPrksqU0

I don't really see a simple way to shift these without limiting the rotation of each wheel, though.

Re: The in-wheel swerve shifter!
 

So they need human input then? I swear I saw autoshifting versions.
I'm opening up the CAD so I can see what happens when you slow down.

EDIT: yup, the dog bounces back and forth like crazy while rubbing against the shifting elements when you slow down, which would completely destroy the teeth on the mating elements. I'm going to find a solution to that.
DOUBLEEDIT: So what would happen is this:
1. The dog slows.
2. The dog is pushed into the other gear by the obtusely angled faces.
3. The obtusely angled face there pushed the dog back.
4. Repeat steps 2-3 until the dog contacts the flat of the teeth and cannot shift out of its current gear.
5. The gear that it is in is forced to slow down slightly until the dog bounced back into the other gear.
Repeat until slowed. There would be a lot of bouncing, but nothing too high load except for the rubbing at the end. Another thing to test under load, although this is a much more serious issue.

Of course, that doesn't matter if you are doing something at a constant 100% speed like loading a spring or climbing, but for drive this seems like a problem.

Re: The in-wheel swerve shifter!
 

I don't have time to look into autoshifting versions right now, but if there are hubs that shift by them selves at certain loads, then they wouldn't work very well even in a test drive train because they would shift under totally different loads than they would experience in this application. My back-of-the-hand estimation of the torque on a bike wheel in low gear puts it at dozens of ft lbs, much different than the maximum of 8.3ft lbs per wheel in a swerve drive on a 154lb robot with 4in, 1.3 coefficient of friction wheels. Additionally, even if it did shift at appropriate loads, the load on each wheel would be different not only in pushing matches and collisions, but also normally because of the robot's weight distribution and the different amounts of power each drive motor runs at during different maneuvers, so you would end up with modules in different gears sometimes.

Re: The in-wheel swerve shifter!
 

This is what I was trying to talk about earlier. As the dog oscillates during slow down / direction changes, the gears are being alternately loaded almost all of the time, though the duration of each individual load condition might not be that high. This is going to resolve as inertia that prevents the CIM from fully slowing down as quickly as a CIM under no load, unless there's a very significant delay between shifting halves.

Another condition that might behave oddly is what happens if you shift under load, i.e. to begin a pushing match. While the dog is "in between" gears, your wheels offer essentially no rolling resistance. What if a wheel is spinning the opposite direction you're trying to drive it? It seems like no matter how long the shift window is, you're going to be dealing with either or both of these problems to varying degrees.

I ain't trying to hate on your design, just trying to figure out if there are ways around these issues.

Re: The in-wheel swerve shifter!
 

Since the S3X hub has an indicator chain for shifting you could mount your shifter up in the swerve drive above the pivot bearing. What you use for a shifter is up to your imagination. One problem is that the 4 wheels would shift at different time do to load on the gears and meshing of the gears. It should be ok for telly op but not for autonomous shifting. The Sturmey Archer hubs that have automatic shifting would not work well for our robots. They would tend to shift each time you slow down. I do not think this hub would work for competitions but it could lead things in a interesting dirrection.

Re: The in-wheel swerve shifter!
 

The dog is never "in between"; it can technically be in both gears at once. However, in that position, there will always be a force that will shift it one way or another into drive.

Hm. I'm looking at the cad again, and I'm seeing something interesting. The dog will actually very quickly "get stuck" in both gears if the dog is moving slower than the gear/hub it is driving. That means that the speed will instantly drop to whatever lower speed the dog is moving at. This would occur once every 1/3 of a rotation maximum, so at ~1400rpm shaft speed there would be 70 of said speed collisions each second. I would want to include part wear in loaded tests to see how much this affects driving. Code would have to allow for taking more time to decelerate, or I could just live with the collisions; that's what shifters and gears do usually when stopping.
Thinking about it some more, and looking at the cad again, it looks like the dog would just shift into the original gear whenever it reached the intermediate position.

Because the cim is putting force in the opposite direction when you shift (reverse cim direction), it will actually shift into the other gear because there is much less resistance that way instead of locking up. I wouldn't go into low gear unless I was in a pushing match anyway or had no load on the robot.

Or a stupid solution: Turn the excess speed into weird snake turns so that you don't have to deal with decelerating at all! Just keep all cims at 100% or -100% constantly. And when you're sitting in place, you can just turn in place!
I don't even want to think about the battery load that would entail.

In the pushing match situation you describe, there would be no pushing match. It would be another robot pushing you in the direction you wish to go, only faster than what the swerve can go at. If the wheel is actually spinning in the opposite direction for some reason, then I would flip the wheel around. More interesting code situiations.

No, I appreciate the input. It would suck to make this, then see it fail horribly and explode when I try to stop.

This swerve would have to have an onboard controller like an XMOS to do all this detection.

Something that's really similar to this is the zeroshift for F-1 racers, but it uses manual shifting with multiple dogs. The angled teeth are the same though.

Re: The in-wheel swerve shifter!
 

The point of this was to have the shifter be compact, not require pneumatic tubing and not take up space outside the swerve module. I want the cim to be mounted above the module instead of being offset by chain.

Re: The in-wheel swerve shifter!
 

Out of curiosity, would the loads experienced by the dog when stopping be the same as the loads on a normal gear or dog when stopping? The dog gets locked in between gears in this until the side it is spinning with spins with the dog whenever you declerate, just like in a normal gearbox slowing down.