Prototype Drive

[ZeroValue]

This is what we are building in the off season. This frame is designed around a half-custom two speed transmission, cantilevered wheels, and synchronous belts. Questions, comments, and constructive criticisms are welcome.

[AndyB]

How are you planning on cutting all those holes? This thing needs to be done in 6 weeks

I like your use of belts vs. chain. Did you design the drive based on a given belt length, or are you using custom length belts?

[ZeroValue]

We plan to have the cnc machine running all night... and day.

[ZeroValue]

We are using .5" wide L series belt, 92 teeth. I did a little monkeying with the wheel center to center distance, then added the tensioners in to take up the rest of the slack. The inventor sync belt tool was very helpful.

[Andrew Schreiber]

Originally Posted by AndyB

How are you planning on cutting all those holes? This thing needs to be done in 6 weeks

I like your use of belts vs. chain. Did you design the drive based on a given belt length, or are you using custom length belts?

Speaking from experience (http://www.chiefdelphi.com/media/photos/29306) it is doable by hand. It just takes a lot of time, and a lot of rookies (And yes, there is its twin in that picture, parts of that were lightened too

I also second the liking of the belt, from what Ive heard that would make it nice and quiet.

[AndyB]

Originally Posted by Andrew Schreiber

Speaking from experience (http://www.chiefdelphi.com/media/photos/29306) it is doable by hand. It just takes a lot of time, and a lot of rookies (And yes, there is its twin in that picture, parts of that were lightened too

I also second the liking of the belt, from what Ive heard that would make it nice and quiet.

I wasn't focusing so much on the holes on the 1x1 crossbars, but more the interesting triangle-like shapes on the main drive rails.

[R.C.]

All I have to say, that this is beautiful. The patterns for CNCing are the same one's I'm using on our offseason prototype.

[sanddrag]

I'd still be a bit weary of going with belts in that application (for fear of jumping, skipping, breaking, etc), but this is one of the better implementations I've seen.

Are you planning to mill all those triangles? How much weight do you save for all that machine time?

[Daniel_LaFleur]

Originally Posted by ZeroValue

This is what we are building in the off season. This frame is designed around a half-custom two speed transmission, cantilevered wheels, and synchronous belts. Questions, comments, and constructive criticisms are welcome.

My gut says that with all those holes you're going to bend that frame on impact with an other robot.

Whats the wall thickness of that box tubing and have you done a stress analysis and bending calculations on the frame parts?

[ZeroValue]

We are using 2x1 with 1/8 side walls for the main frame members, and 1x1 with 1/8 sides for the two cross pieces. We haven't done any testing, but we are confident that it will hold. Last year our robot fell off the wall for every match, and we had over 20% more material webbed out. there is a forum somewhere here about basic cad for that robot that i posted when I was still green with the cad design/f.i.r.s.t., search for "tator".

The weight lost/cnc time ratio is fairly low. It's mostly a way to get some experience with the small cnc mill in the shop. Last year we sent the cad to the micron shop and had them machine and weld it. This year we plan to do more of it in our own shop. All of the kids in the shop during the off season mechanical team meetings have some experience with manual mills/lathes. We just don't know anything about the cnc part.

[ZeroValue]

Here is a quick update with the welding plans added.

[BanksKid]

i have two words.......

WATER JET

it wouild also seem that you could loose alot of weight and machining time if you used flat plate as opposed to the tube frame.... from what i see, it appears to be slightly overengineered strenght wise..... but thats just me...

[Dick Linn]

I'm not a fan of cantilevered wheels in general. Make sure the side rails are stiff enough not to twist.

[AdamHeard]

I can't really speak for the belting, but everything else is looking like a decent start.

Don't worry, both the pocketing and cantilevered wheels are features that have been done before by teams, so assuming you've done the math, it should hold up just fine. What kind of machines do you have available, as that can affect how you would optimize your pocketing to minimize production time.

I'm personally a big fan of the standard hole pattern on the top as well; works out to be extremely convenient/worthwhile in the long run.

The slots for fasteners for what appear to be bumper mounts also look rather small (1/4"?). I would increase the fastener size on these as I imagine it would work out better in the long run (I'm imagining the a smaller diameter fastener tearing the plywood and becoming loose much faster than a larger one).

[Dick Linn]

Originally Posted by AdamHeard

... and cantilevered wheels are features that have been done before by teams, so assuming you've done the math...

I doubt that most have done the math. And a cantilevered wheel on a 1" x 2" aluminum frame member that has been skeletonized makes me leery of the durability. Obviously it depends on the amount of stick-out, but I was surprised at the twisting forces we encountered when using full 2" x 4" x 1/8" box aluminum. Your results may vary.