pic: Team 2220 Blue Twilight Octocanum Offseason Project

[cadandcookies]

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[CENTURION]

Are you using threaded rod as an axle for the traction wheel?

I ask because we've tried doing that before, and it didn't work very well, the axles bent after only a few minutes of driving. Then again, I think we were using pretty small rod, I think it was 3/8", but it might have been 1/2", I can't remember exactly.

Also, what is keeping your wheels centered on the axles?

The module is looking pretty excellent though! Can't wait to see the finished product!

[Boe]

which wheels do you plan on having at the corners of your drive?
Also what are you planning on for a gearbox? It appears that the sprockets on both wheels are the same size is that correct? Overall looks very nice hopefully i can see it sometime at an off season event when its done.

[lemiant]

Based on the fact the double sprockets are on the meccanums I think it's a safe guess that they have the traction wheels on the outside.

[Jeffy]

Originally Posted by lemiant

Based on the fact the double sprockets are on the meccanums I think it's a safe guess that they have the traction wheels on the outside.

I don't see this as conclusive evidence.

For the OP,

If you have decided, can you tell us why you decided on the placement of the traction wheels on the inside or outside. I think there are a few obvious pros and cons to each, but would like to hear your view on it.

[Trent B]

One comment I would make is with the sprockets chaining the traction wheel and mecanum together, did you pick the wheel separation distance to ensure an even number of chain links? It is a bit harder to put the modules together under tension, but never worrying about throwing a belt or chain is great.

[cadandcookies]

One comment I would make is with the sprockets chaining the traction wheel and mecanum together, did you pick the wheel separation distance to ensure an even number of chain links? It is a bit harder to put the modules together under tension, but never worrying about throwing a belt or chain is great.

Yes! We saw the multitude of posts on that subject and ensured that we were spacing the sprockets at a multiplier of the pitch for #25 chain (.25").

If you have decided, can you tell us why you decided on the placement of the traction wheels on the inside or outside. I think there are a few obvious pros and cons to each, but would like to hear your view on it.

The current plan is to have the traction wheels on the outside. The primary reason has a lot to do with one of out mentors, who is pushing us to develop this for the 2014 season (which may or may not make sense). Our primary rationale was that, in a competition bot, one of the main benefits we wanted from octocanum was the ability to go in a very straight line without too much feedback correction (for autonomous mode). The main thing we were weighing this benefit against was being able to use a single piston on each side to actuate.

Are you using threaded rod as an axle for the traction wheel?

No, we're using 1/2-20 Grade 8 steel cap screws. We've used them on previous robots with much success-- we haven't managed to bend one in competition yet. We're still running our 2012 competition bot on the same bolts we used for our two regionals, plus championships and several demos and off-season events.

[Trent B]

Fortunately the size of the pistons you need to shift is pretty small, I think ours had a stroke of 1" tops, and a bore of 1 1/16" or so, we also plumbed them all off of 1 or 2 solenoids, I can't remember what we decided on at the end of the season. You don't have to use air to pull the traction wheels back up, robot weight should be more than enough. Also, the bot was downright hard to move if it stopped in traction mode.

[cadandcookies]

Originally Posted by Trent B

Fortunately the size of the pistons you need to shift is pretty small, I think ours had a stroke of 1" tops, and a bore of 1 1/16" or so, we also plumbed them all off of 1 or 2 solenoids, I can't remember what we decided on at the end of the season. You don't have to use air to pull the traction wheels back up, robot weight should be more than enough. Also, the bot was downright hard to move if it stopped in traction mode.

Yeah, this confirms what we were thinking about the process. I believe Aren mentioned something about "cute little 8lb springs" too.

[Madison]

Originally Posted by Trent B

Fortunately the size of the pistons you need to shift is pretty small, I think ours had a stroke of 1" tops, and a bore of 1 1/16" or so, we also plumbed them all off of 1 or 2 solenoids, I can't remember what we decided on at the end of the season. You don't have to use air to pull the traction wheels back up, robot weight should be more than enough. Also, the bot was downright hard to move if it stopped in traction mode.

Could you explain this further?

If you don't use air to retract the traction wheels, won't the end result be having both the mecanum wheels and traction wheels touching the ground simultaneously?

[Trent B]

Was trying to figure out what the confusion was, then I realized.

We also have a small spring (maybe 1-2lbf tops) that pulls back on a small "finger" sticking up from the plate by the axle lifting the traction wheel the remainder of the way off the ground.

Here is a side profile picture with the "finger" which sticks up through a milled slot in a chassis tube.

http://www.teamneutrino.org/assets/r...drive/side.png

[cadandcookies]

Originally Posted by Boe

Also what are you planning on for a gearbox? It appears that the sprockets on both wheels are the same size is that correct? Overall looks very nice hopefully i can see it sometime at an off season event when its done.

Sorry I missed a couple of your questions.

We're planning on either running them through something like the VexPro double reduction gearbox or a custom solution (we can always use more practice!).

The sprockets are indeed the same size-- and they'll probably stay that way, unless we find a good design reason to change it. We have a bunch of 32t #25 sprockets lying around, and might as well use them for this!

I hope we get a chance to show it off at an offseason event!

[Boe]

Originally Posted by sentientfungus

Sorry I missed a couple of your questions.

We're planning on either running them through something like the VexPro double reduction gearbox or a custom solution (we can always use more practice!).

The sprockets are indeed the same size-- and they'll probably stay that way, unless we find a good design reason to change it. We have a bunch of 32t #25 sprockets lying around, and might as well use them for this!

I hope we get a chance to show it off at an offseason event!

You could gear the traction wheel slower because i would assume in a competition the mecs would be the primary drive mode except during auto and when you encounter defense. changing the speed of one of the wheels would essentially give you a two speed drive train with your high gear being omni directional.

[Gregor]

Originally Posted by Boe

You could gear the traction wheel slower because i would assume in a competition the mecs would be the primary drive mode except during auto and when you encounter defense. changing the speed of one of the wheels would essentially give you a two speed drive train with your high gear being omni directional.

The traction wheel is already smaller, which will make the robot slower already in traction mode. Whether that is slow enough the team needs to test and play with.

[Trent B]

I don't have the exact dimensions off the top of my head but I think neutrino went from a 4" omni to a 2.75-3" traction wheel which provided a substantial speed difference. With the current size difference between their mecanums and traction wheels they should see a similar if not larger effect.