pic: Drivetrain Concept
 

Re: pic: Drivetrain Concept
 

Look like a really sweet idea. Only question is will it strafe straight?

Re: pic: Drivetrain Concept
 

Looks good. I would be partial to a regular 6WD with the cims in that configuration (for space), but omni is cool too.

How is this going together? Screws? ARe you sure that you can assemble it right?
What's the material?

43lbs is pretty heavy. There's probably a problem somewhere.

Re: pic: Drivetrain Concept
 

It has a lot of motor weight 6cim/2miny cims..... its a lot of weight in motors.
Even more then a swerve would be.

Re: pic: Drivetrain Concept
 

Your Motor weight would be there anyway.



Otherwise, looks great. Just a couple questions...

1. Are those modules made of lexan? Kinda hard to tell on the render... If so, what have you done to prevent flexing?
2. Is the slot in the box large enough to fit both gears in?

Re: pic: Drivetrain Concept
 

Strafing should be straight, and it should be possible to do anything that a swerve can do as well.

Assembly would either be bolts or rivets, but I am thinking mostly rivets. The frame is made by 1" x 2" aluminum box tubing, and 1" x2" u channel.

For weight, roughly half is in motors, and I could drop a set of CIMs and change the reduction pretty easily to reduce weight. Also, I'm planning on adding some kind of lightening cutout to all of the frame members, which should cut down the weight some as well.

Re: pic: Drivetrain Concept
 

Pre 2014, I would say the frame members are way over sized and using thinner metal and a little redesign on the frame would have been recommended for weight. After watching the frame failures in 2014, I would not say it is over built. Still there are other methods to absorb the impact forces with less weight.

Re: pic: Drivetrain Concept
 

Keep in mind that there are 3 additional CIM motors in this setup that you normally won't see on standard butterfly/slide drives. To drop some weight we can remove two CIMs and one mini CIM without sacrificing much as a majority of them are run with 4 CIMs. 2013 and 2014 have been the only years we've seen 6 CIMs and 4 mini CIMs in the kop so robots have been getting heavier just in motor weight alone. Our past year's drive was 6wd six CIM shifters came in around 40lbs so this base gives us more for a few more pounds. Remove the center slide module and you can remove more weight and it becomes a standard butterfly.

This is also a lot easier to build, program, and drive compared to a full on swerve drive so its a more feasible project for us to try out with room to make it lighter.

Nice work Eric!

Re: pic: Drivetrain Concept
 

I'm not gonna lie this drive looks beautiful.
I'd love to see it in action- is this a planned off-season project?

Re: pic: Drivetrain Concept
 

A few things that don't pass the "that doesn't feel right in my gut" test --

1. Change the channel to rectangular tubing everywhere. Channel is much less rigid in torsion than rectangular tube.

2. The strafing omniwheel is not well-supported in the frame. You're removing a lot of material from the 2x1 cross-members for chain clearance and leaving very little wall where the U-shaped cutouts are. The weight of the robot, when it's sitting on that strafing wheel, is supported almost wholly across the four thin gussets you're using to couple those 2x1 cross-members to the rest of the frame.

2a. That all presumes, of course, that you're actuating the strafing wheel downward. It's unclear if that's the case. Otherwise, I'd be concerned that the normal force acting on that wheel alone will not be sufficient to move the robot sideways.

3. Gusset the joints more to give you some additional support against wracking to whole frame into a parallelogram.

4. It's hard to be sure from this view, but it looks like you're mounting the CIMs against the outer flange and race of the bearings. That gives me the willies.

Re: pic: Drivetrain Concept
 

How does the center drop down wheel work? Is it one wheel or two wheels?

Re: pic: Drivetrain Concept
 

This is impressive. I really like it. I'm assuming you want suggestions so here are a few:
1) I would change the framing to 2 x 1 x 1/16 tubing (someone pointed out to me that this is lighter as well as stronger than pocketed 1/8th material).
2) The structure for the middle module could be made simpler. I'm not sure which part is spring loaded so I may be missing something. You seem to have several pieces of flat bar (3/16?) acting as stiffeners across several of the frame members in the middle. This could be redesigned to use sheet metal or standoffs to save weight and space.
3) Aluminum gears? I'm assuming that's what you're using but just checking.
4) I would take your high gear speed down to 16 fps. Just my preference after running a 20 fps drivetrain this past year. We made the change to 16 fps and really liked it. That was with 4 cims though so you could save weight by taking 2 out or leave the ratio the same and using 6.

Re: pic: Drivetrain Concept
 

Wow, thats a ton of CIM motors. I really like the layout of the side modules and the gearbox in the frame.

A few comments/questions:
How do you plan on retaining the bearings and locating the module axially?

The shaft that drives the module is going to be really difficult to do the way you have it. I'm assuming there's 3 bearings supporting it, two on the inner frame part, and one on the outside. If you had only two, I'd worry about the shaft bending. It'll be tough to get those three holes aligned with each other, especially if you're welding it. If one of those holes is in the wrong spot, you'll "overlocate" the shaft and it'll bind up. You do have the advantage of using hex bearings, which usually have a pretty sloppy fit.

If your frame bends at all, your center wheel won't touch the ground. The slots that have been cut out to let the chain by are weakening your center module. These wheels are usually articulated so that you have enough force on the wheel so that it won't slip. You also want to avoid the opposite, where the robot rocks side to side and one half of the drivetrain is off the ground.


2 x 1 with .063" wall box tubing is a pain to find and is weaker than I'd be comfortable with for a frame. We used .125" thick on our robot, in roughly the same configuration as show above but with a bellypan and we still managed to get bent.

If you want to save weight, you could get .100" thick tubing from vex pro. If you're really desperate, you could probably put some lightening holes in the sides.

You said you had the ability to adjust the drive ratio with the sprockets on the wheels. I'd wait until you know what distance you want the robot to travel quickly, then gear to get the best acceleration for that distance. That being said, 20 fps is on the fast side. If you do go to four CIMs, I'd take gear to go slower, but that's my opinion.

Re: pic: Drivetrain Concept
 

This is interesting, I like using the pistons on the side of the module to allow the CIMs to be mounted inside the rail and not waste the space to the sides.

Have you thought about supporting the outer side frame rails somewhere along their length? I am not sure how bumpers would mount to this but I would be very worried about those channels bending in and contacting the CIMs pretty quickly.

Re: pic: Drivetrain Concept
 

Very cool, I haven't looked at it with enough detail to comment on it's structure, other than the fact that you should really not use channel or 1/8th inch aluminum in something like this. 43 pounds seems pretty steep, but once the tubing was switched I think it would be a bit more reasonable. If I were to build it I would put 2 full CIMs on the center omni wheel and use 4 CIMs and 2 mini CIMs on the outside, but I think this depends on the year, and in some years your configuration might be better.

Any plans on building it?