Re: [FTC]: Drive Platform- Design Exercise
 

We received the AndyMark wheels and v-belts. The inside-out v-belt fits snugly over the wheel. The cogs grab the churro nicely.

Re: [FTC]: Drive Platform- Design Exercise
 

Looks like a good fit, on both the wheel and the churro! Are you planning to use adhesive between the wheel and the belt?

Re: [FTC]: Drive Platform- Design Exercise
 

It's tight enough not to slip in rotation. I'm thinking a thin bead of heat glue would keep the belt from moving laterally. Rubber cement would work too.

Re: [FTC]: Drive Platform- Design Exercise
 

Same two primary answers I was thinking of, with a slight advantage towards the rubber cement. CA is too likely to be brittle under game stresses. Hot glue doesn't really stick to anything, and might not grab the smooth tire tread well. Rubber cement is more flexible than either, and would provide more friction even if it doesn't serve as an actual adhesive on one side or the other. Contact cement is flexible, but would be a royal pain to get right. Silicone glues are also worthy of consideration, for the same reasons as rubber cement.

Re: [FTC]: Drive Platform- Design Exercise
 

OK- time to start building the prototype. The plan is to build one half of the chassis; Chassis Rails, 2 wheels & 2 motors. We'll test on "Mountain" for ability to climb.

Re: [FTC]: Drive Platform- Design Exercise
 

Here's a Bill of Materials (BOM) for the prototype:

Link to Excel spreadsheet with BOM and other analyses: Chassi Build_cr 03oct15.xls

Re: [FTC]: Drive Platform- Design Exercise
 

We've made some modifications to the design:

1. We had used 2" for chassis clearance of balls and blocks. This is incorrect as the ball is 2.8" in diameter. We raised the motors to clear 3".
2. We made the Chassis Rail 4" tall and symmetrical about the wheel axle. This allows a standoff at top of Rail.

The BOM in the previous post has been updated.

Re: [FTC]: Drive Platform- Design Exercise
 

The first fabrication activity will be to modify the 8" AndyMark wheels. They will be turned on the lathe to narrow to 1" and allow the hub to attach within the 1" width.

Re: [FTC]: Drive Platform- Design Exercise
 

Re: [FTC]: Drive Platform- Design Exercise
 

I found an interesting robot with similar design. The video may shed some light on how the bot will drive on tiles...

LINK to video

Re: [FTC]: Drive Platform- Design Exercise
 

Rubber cement is fast drying, but Shoe Goo urethane adhesive is way stronger in the key spec of its => peel strength.

We are evaluating a strange design that uses four overlapping pairs of half wheels that have their flat sides oriented 180º out of phase within the four pairs, and each pair is driven by one of four motors..

By correctly spacing the axles within the pair and by optimally separating the pairs on each side (front to back), we expect them to roll over the churros where we have plastic and them climb them on the high zone churros.

Our Plan B wheels are going to be 8" AndyMark, like yours, but with thick walled pieces of 5/8"-3/4" OD surgical or urethane rubber tube pieces tied around the circumference to function as as large and somewhat individually "floppy" cleats.

Notches in rim will keep the cleats' tied on with the capture cord at properly equal spaced locations around the circumference of the wheel. Shoe Goo adhesive may be needed to better stabilize cleats against the wheels' urethane if cleats flex too much. with just cord holding them on.

We considered your style of cogged belt too, but felt the cogs might be a little too shallow for maintaining good grip engagement with the churro bars.

Appreciate all the time spent documenting your design and build process here.

-Dick Ledford

Re: [FTC]: Drive Platform- Design Exercise
 

A good quality CA will bond belts and wheels in this application. Medium set will give a little more work time. Be fast if you use it.

Re: [FTC]: Drive Platform- Design Exercise
 

Good idea using Shoo Goo- thanks!

I converted the above robot's SolidWorks model to OnShape here: ASME CMU Robot 2004

The design has nice mechanisms for arm using servos.

Re: [FTC]: Drive Platform- Design Exercise
 

We tested the chassis & wheels on the "Mountain" today; no motors yet:

• It's not certain that the rig will climb as hoped. Turning the wheels by hand doesn't give enough info about slip, as the front and back wheels work together and we couldn't apply the torque on both in sync.
  
  
• When a wheel is resting on 2 rungs, I'm concerned that the bot will get stuck; the notches could bind on the churros and not climb forward. Momentum will probably be a factor in this.
  
  
• We did have a problem with the chassis hitting the churro as shown below. Something's off with my CAD model, the mountain CAD, or both.

Re: [FTC]: Drive Platform- Design Exercise