pic: 1714 Polycarb prototype Crab Drive (backdrop1)

[AJ R]

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.

[Akash Rastogi]

Originally Posted by AJ R

Yes, the final one will be made out of polycarbonate. After four years of building with it, we are confident it will hold up.

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

[Andrew Schreiber]

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

[AJ R]

Originally Posted by Andrew Schreiber

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

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)

[xanarchyx]

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.





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.

[xanarchyx]

... I cant post quick enough...

[J93Wagner]

Originally Posted by xanarchyx

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.





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.

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.

[AdamHeard]

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.

[EricH]

Originally Posted by AdamHeard

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

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...