Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Yes, the final one will be made out of polycarbonate. After four years of building with it, we are confident it will hold up. As pictured, the top and bottom are acrylic because we wanted to laser cut them. American Acrylics is getting a CNC router, so they will be made out of polycarbonate eventually.

The belt is quite grippy. I dont have any numbers, but it seems to hold quite well. It is a single sided belt. We tested a double sided belt, but they have a nylon backing on both sides, and are less grippy.

Keep in mind this is only a prototype, and was put together quickly and cheaply. We do plan to put cross bracing to prevent flexing, if it needs it. Right now, we are just using set screws, but plan on using a hex shaft held in with snap rings. One of the things we like best about the module, is the belt for power transmission is also used for traction. We are planning to use a wider belt in the future.

The wheel has a groove the width of the belt for the belt to ride in. With it properly tensioned and aligned, it will stay on.

As for the DP of the gears, I will have to get back to you Wednesday.

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Is this backed up by any sort of FEA/ Stress testing?

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Also, not to seem like I am picking on this but how are you tensioning the belt?

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

The tensioner is on the other side. It is easier to see in this picture.
http://www.chiefdelphi.com/media/photos/34298?
The belt rides on a bearing and the shaft is moved outward by turning the screws. The hole through the shaft is threaded and the hole in the module is not. Hope that clears it up. (no pun intended)

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Another piece to making the ultimate Van de Graaff generator 1714?!?! Looks very elegant and awesome! All you need is to make propellers out of polycarb so you can make your robot fly (hmmmmmm maybe they are the secret manufactures of Wonder Woman's invisible jet............)

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

shhhhh don't tell them about that prototype! We're still keeping THAT under wraps... :cool:

Maybe it's just me but seeing these pictures makes me a little more excited about swerve... If anything, you guys have certainly made something really, really cool. :D I hope you guys let me thoroughly ram and smash a test chassis (if one gets built in time). You know, "load testing"... yeah... mhm.

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

OK OK
Let me clarify some stuff

1. It WILL be made of polycarb, when fabricated properly it is as rigid as aluminum.
(but thank you for the warning, we will take it into consideration. Although 3/8 in polycarb is more rigid in small distances than people think.)

2. This is a RUFF prototype, but it is the ruff size/dimension of the real one. ( The "pulley" for the belt will be bigger for more teeth engagement.)

3. Bearings and bevel gears are just what we had laying around. They are not the final ones.
(the bearings are the really crappy kit chases ones i believe.)

4 I know I'm missing stuff, But this was just a quick update, although i would like to say. I believe it is beautiful.

:D



OK i remembered, we are working on mounting it on the front of a frame with 2 casters in back to test it, although pre-tests of the grip and pull of the 3/8 in belt was kind of amazing. We will probably still go with thicker.

Btw, Belt on carpet = Amazing Grip.

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

... I cant post quick enough...

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Great, looks like you have a better start than I originally thought.

I also have access to last year's crab drive design if you're interested.

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Curious, did you guys decide to make a crab drive out of polycarb because you like polycarb, or did you do some sort of analysis, disscussion or pros/cons, etc... that lead you to this.

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Fixed...

Adam, read the 2007 design book for about the first robot they made out of the stuff. If it weren't for all the stickers and lights you have to have, it would have been virtually invisible. I haven't seen one of theirs since... or seen pictures, either.

They're clearly pretty good at working with polycarb.

Bonus points to Adam for getting me started on a pun trail...

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Well, we mainly work with polycarb, in fact we a based out of an acrylics shop so all of our tools (even the drill bits) are designed for plastic. That is the main reason we use it. Also, over time we have found it is very unique, and as i have stated, if you know what your doing, polycarbonate can be used everywhere you use aluminum.

As for testing, we haven't done any technical testing of polycarb vs aluminum...Aluminum would be lighter, but the fact that we don't even have a wielder makes it a lot harder to work with.

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

Heh. Technically in 2007 we had a kit frame hidden in there somewhere. This year, the only metal in the whole robot was in Toughboxes, drive sprockets, motors, transmissions, shafts, and the controls; we used Poly Cord extensively to connect belt runs too (though not for drive, we're not THAT hardcore anti-metal :rolleyes: )

I think a swerve module out of this stuff should open an interesting in-team discussion as to what the limits of our fabrication abilities are with the relative commitment to polycarbonate as a build material; projects like these that "push it" of course being extensively tested in the preseason to ensure they would work. It is significantly faster and easier for our team to fabricate out of polycarbonate; it's not all "cool factor" (though I can't say that doesn't play a small role). Every team's shops have their limits, maybe we're approaching ours? We'll find out!

Clearly.

(I was tempted to make this whole post in clear text...)

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

LOL, I think we got started on pun trails, which I haven't found again.

(Or did I?)

Re: pic: 1714 Polycarb prototype Crab Drive (backdrop1)
 

...o lord not the puns.