Yeah… I haven’t really figured out what to do about bumpers. Mounting them at normal height would also make the suspension pretty useless, so I have no clue what to do.
I haven’t selected a gearing ratio yet, but the drive motors have 2-stage VP’s on them, allowing for a range of different ratios.
My plan for getting the frame to stay put is to have a differential bar running across it. This way, when the left side goes down it rotates the bar, causing the right side to go up and cancel out its motion. Because of this opposite reaction, the frame will be able to hold itself up mechanically and without the use of motors or weights.
Yeah, the amount of gearing on this thing is insane. Instead of using a gearbox for the differential, though, I plan on using a bar that will act as a differential. This way, when the left rotates down, the right will rotate up proportionally and cancel out any tilt, allowing the bot to stay upright without the use of motors or weights.
Best of luck to you.
I’d really love to build this, but… it costs like $2000 just for the drivetrain, and I’m not even sure if it would work. I’m prototyping a swerve drive using a 3D printer, but even that requires a lot of components. I think it would be cool to 3D print a little model of this for my desk, though…
I chose to put the 775’s vertical mostly just for the aesthetics, to be honest. Curiosity has some kind of hubbed (or very small and hard to see) motor for its wheels, so I wanted to try to imitate that. Also, I heard that my team had a really bad experience in the past using VP’s horizontally directly to the wheels.
Also, how would you recommend utilizing CIM’s for drive in this design? As far as I’m aware of, CIM’s can’t be mounted to VP’s and creating a custom gearbox for this would be either too big or an absolute nightmare.
Thanks a lot!
CIMs absolutely can be mounted to VersaPlanetaries using a CIM Adapter. You have to pay attention to the load rating guide to make sure you don’t use them above their rated torque, but other than that it’s no problem. You should also pay attention to that guide with the 775pros, because I would think you are starting to approach that limit with (what look like) 6" wheels driven 1:1 off the VP.
As far as directly connecting the VP to the wheels, you’re right that that’s not such a good idea. VPs don’t like much axial or radial force on the output shaft, and direct driven wheels tend to give both of those (especially if not well-constrained). You could, however, use a small spur gear or belt or chain reduction between the VP output shaft and the wheel shaft so those forces aren’t transferred. All of those options are more efficient than bevel gears, and would allow you to rotate the modules 360*. That would also allow you to lower the reduction in the VP, which will bring you further from the max rated torque and maybe even make your VPs smaller.
If you’re not set on using VPs, you could use CIMs with a Toughbox Micro or Nano. They’ll give you plenty of reduction and no worries about forces on the output shafts. The hardest part would be integrating them into your design, but they aren’t too big so you should be able to find a place for them if you so choose.
Yes CIMs can be mounted to the VPs if you’re willing and able to cut the hardened shaft of the CIM motor.
It really isn’t that hard to cut. My team has cut a number of them over the years with just basic hand tools.
- Put the CIM in a vice
- Mark the spot you want to cut with a scribe (marker will work if you don’t have a scribe)
- Plug the CIM into a battery to turn it on
- Slowly, using some cutting fluid and all the proper safety precautions, press a hacksaw against the marked line to cut. Stop when there’s ~1/8" diameter left
- Unplug the CIM and let it come to a stop
- Cut the rest of the way through
- Finish off the end with a file
This method hasn’t failed is yet, and it’s basic enough that any team can do it. If you’re really worried about safety, you can cut the shaft without turning on the motor using a good amount of cutting fluid and elbow grease. It really doesn’t matter if the end isn’t perfectly flat for this application.
Wow, really?! I didn’t know you could do that 
I’m working on finishing the full model of this first, and I’ll integrate that in the second revision!
That looks absolutely amazing! I’m a freshman with no money though.
It’s for university/college students, so there is time to plan your design. 
This will work nicely with the replay of the 2010 bumps in next years game.
The Mars rover linkage suspension was designed to keep all the wheels pointed the same direction while allowing them to go up and down. With swerve modules, I don’t see that this makes much sense. I’d put those modules on tripods mounted to the chassis with ball joints, or perhaps orient the lower bearings perpendicular to the uppers, and arrange the nominal drop points of the modules to be something more like a regular hexagon than two lines of three.
[Note: also posted in the Conspiracy? thread.]
Sorry, I don’t quite understand what you’re saying. T-T
I don’t think having swerve modules undermines the drivetrain’s differential at all, as the modules are able to point forwards when need be, and allow the bot to have greater maneuverability when turned. You’ll notice that the rover utilizes swerve modules as well on four out of its six wheels, with the middle two locked in place. This allows it to turn about its center, as opposed to having to drive like a car to turn 180 degrees.
Of course, I may be wrong/misinterpreting your point, but I think that using swerve drive modules here is an acceptable (and useful) application.
I’ll definitely think about it. The MIT rover competition also looks cool, though, and I know someone who competed in that a couple years ago. They had swerve drive and a 6-axis arm, and their bot was totally awesome to look at. I never got to see it working, though.
I never thought of this. This sounds like a fantastic method for teams that don’t have some decent machinery.