pic: Swerve!

Okay so I don’t know how to write a description in CD media… I tried…

Seems as though there has been a virtual crab-fest going on, on Chief Delphi right now!

Thought I’d share my own design, which has been in the works since last season.

Seeing how my club has very limited machining capabilities I tried to design this with as few machined parts as possible. The wheels are 4" traction wheels from Andy Mark inc. and the transmissions are obviously from the kit.

The upper frame is made from 2" by 1" boxed aluminum. The lower frame is strictly for protection and can be raised to give more ground clearance.

Right now I have the motors set up in such a way as to allow it to be steered like a car, like a swerve, or like a conventional tank. I am still debating whether it might not be better to allow the corner wheels to be turned in such a way as to allow it to spin in a perfect circle.

Can you see any way to make this simpler?
Comments appreciated…

Just go to the image in cd media and click under it and copy the discription there, that should work.

I like the design alot it seems pretty simple, I like the way you are getting power transmitted to the wheels pretty inventive. As far as being able to turn in a complete circle I think it’s took early in the design to worry about the fine tuning like that, good idea asking for suggestions and input though. I am impressed with the many uses for those kit gearboxes. Anyway, pretty cool looking concept so far that is just my two cents on it.


I think what he meant by a perfect circle was that the wheels would all be angled 45* relative to the frame such that there would theoretically be no side-resistance when turning in a circle (unlike in a tank setup).
Just a question, are the modules made from box aluminum? It looks like they are, and if not they might save you the hassle of having to make 4 plates per module.

Nice design as it used KOP items and simple framing materials. My only suggestion, considering that our team has no swerve experience but is working a summer proto-type, is that you consider the following.

I would prefer using a window motor with it’s worm gear transmission to hold the steering position verses the Globe and it’s back-drivable planetary gear system. Maybe this is not an issue and it is a waste of the window motor which could be needed for an arm or other manipulator. I do like the ability to steer two modules together. This too is something we are considering. Adds a few more options than having all four steered together and I don’t know how one steers all four seperately without using a half of the KOP motor inventory for just the drive-train. :ahh:

The window motor is back drivable, it’s just extremely difficult and you’ll more than likely break something in the process. Also some of the window motors are known to have a significant amount of back lash (although there was a trick with using keystock to solve this problem).
Also, take into consideration, how much force does it take to back drive the wheels? When will you be encountering this force? The modules are shielded on all sides and if another robot is sticking its manipulator into those modules to try and move them then they’re going to encounter a penalty. I’m not saying using the window motors is a bad idea, I’ve seen teams use them instead of the globes; but same vice-versa, many teams use the globes to steer their swerve modules and have had no problems with back-driving – since both motors seem to get the job done, I think that whether they are backdrivable or not shouldn’t be the determining factor for whether they should be the steering motors or not.

Yes that is exactly what I meant, and yes as techtiger1 said it is probably too early to wory about this. This decision can only be made once we have seen next year’s game and know what kind of advantages it offers. This may be a useful alternative to a turret though.

Yes they are made from box aluminum. I owe my respects to Joe Widen for coming up with this brilliant idea. I was originally planning to do exactly that, and make the modules out of four plates.

I used the globes primarily because I have seen other teams using them successfully in this application. I also knew they were stronger and lighter. Not sure about the backlash, but it should be easy to swap motors if the need arises.

I must be missing something here. To me, it looks like you gear up by a factor of about 2 from gearbox to module then gear down by a factor of about 2.5 in the module to the wheel. Also, I’m not seeing how the globe motor actually connects to the modules to rotate them.

Other than that, it looks pretty good. How much does Inventor say it all weighs (with material properties properly set of course)?

It’s the kit gearboxes, the original chain and sprocket reduction between the KOP wheels and the KOP gearboxes wasn’t much to begin with. Even with not-so-very-large reduction, he’s using 4" wheels. Seems about right to me, correct me if I’m wrong, though.

And just a guess, the globe motors are attatched to sprockets which drive sprockets that are connected to the modules under the frame?

those 4 lower box tube members look like they are asking to get smashed in. swerve drives move around crazy and Krunch stuff. there should be allot more structure there. i would like to know how your going to keep tension on the chains. there are allot of chains in that frame and a long distance for them to cover over a frame that will flex dynamically. its quite an engineering feat. i would like to see what you come up with to pull it all together. please keep posting

Tytus just about said it all. Sandrag has some very good points also. Going back to the conversation about the window motor if you used it to turn the modules and something else would probably break first before they back drive. I mean it’s quite a feat to accomplish.

Your powers of observation do not deceive you. That is exactly correct.

I designed it to move at the conventional 8 fps. Using the KOP transmissions and 4" wheels the chain reduction worked out to be about 1:1. However, using a 10:28 reduction in the modules allowed them to be made smaller, so I decided to gear the speed up outside of the module and then gear it back down again.

From the looks of it I forgot to replace the sprocket on the transmission with a 28 tooth to give me a perfect 1:1, but you get the picture.

As for the globes they will be turning chains that enter the frame through a slit an inch down.

As Tytus said I am still working on how to tension all the chains. So I have not added them in the CAD yet.

Each module - 4.3 lbs.
The Frame - 25 lbs.
Transmissions w/o Motors - 5-7 lbs.? (not sure)
Chain - 10 lbs.?
Total - 64.4 lbs.

Keep in mind that this is still in the prototype phase. There is a LOT of weight that could be removed. After I’ve worked out all the details then I’ll focus on making it lighter.

By all means smash away!

That frame is there simply to protect the modules. It provides little structural support and can be bent and twisted. I am probably going to cover it with poly-carb to add additional armor.

I think his point was that if they get smashed in it will greatly affect your ability to steer.

As for weight reduction, I’m told you can take a considerable amount out of the kit gearboxes.

It’s better that way… trust me. Yours is the only description I haven’t had to click another page to read. Thank you for that!

As far as the design, it looks great, just watch out for pinch points in that configuration. It’s a great theory, but some guards would be nice in the final product.

Good luck, and happy building! :slight_smile:

Here is an update.

A rough chain path has been added.

As for the globe, I did some research and found that the globe is especially sensitive to side loads. This might explain some of its problems when used in this kind of drive. So long as the globe’s shaft is well supported it should do fine.