pic: 6 Wheel Drivetrain

[gallo26]

Originally Posted by Tom Line

I would be concerned with the front and rear driven omni-wheels. In our experience, having no side-force resistance to turning will lead to a robot that is very difficult to accelerate in a straight line.

We've used that drivetrain in 2007 and 2008. 2007 we used 4 banebot KOP gearboxes. 2008 we used an AM supershifter. Both years we had no problem with the robot driving straight. Even in autonomous with a little help from a gyro, we were able to drive straight.

Originally Posted by M. Mellott

You plan on using 25-series chain to drive the omnis...how will you tension the chains? Also make sure the alignment between each pair of sprockets is acurate.

I was considering adding those tensioners that Andymark sells for #35 but purchase them from McMaster for #25. But now I'm going to just cut slots into the plates and have an idler sprocket with a shoulder bolt. That's always worked for us in the past. And lok-tite is a definate for everything we use

Originally Posted by Jeff 801

It appears as though you are using AM toughboxes, you might want to leave the cover over the gears to keep dirt and FOD out of the gears and grease.

I agree with that. It's not a lot of weight, and I'm going to put the aluminum one back on. Should look nice too. Thanks for the tip!

Originally Posted by Chris is me

I'm still a little confused as to why this chassis is being built with weight in mind (other than to keep it liftable, roughly under 150ish pounds), but it looks simple and effective.

I'm assuming that there would be cheerleaders and people who cannot lift as much as we can. With safety in mind, I want to keep the actual weight of the robot between 120-150lbs. That includes bumpers around the perimeter, 2 batteries, and the rest of the robot. With this 30lb drivetrain, assuming bumpers are at a max of 18lbs like FIRST. There is approx 45-75lbs for electronics, and the manipulator.


Thank you for all for your input

Bryan Gallo

[AdamHeard]

I'd recommend ditching the wedgetop tead and omni wheels for normal solid rubber wheels like colsons.

They're cheaper, and won't need replacing/maintenance.

[cdebo]

Bryan,

Nice work. I am trying to get my class to evaluate different disigns with different materials. Could i get a copy of the CAD file? It would help with the analysis.

[R.C.]

Originally Posted by cdebo

Bryan,

Nice work. I am trying to get my class to evaluate different disigns with different materials. Could i get a copy of the CAD file? It would help with the analysis.

There are some bots here:

http://team1323.com/cad/pages/teamhosting.html

If you would like to check these out, Bryan has 5 of his bots on there.

-RC

[gallo26]

Yeah! there are 5 up there. 2006-2009 are very durable tank drive drivetrain systems. They've been through pretty harsh competitions, and worse yet, off-season, and they've lasted through that. If you have any questions about any of those designs i'll be more than happy to help. PM me or email me.

I'll try to post more drivetrains on the team hosting website. I have a few on here, along with our T Shirt Shooting Robot the Screamin' Eagle! I just need to finish up some work on it.

[DonRotolo]

Nice work.

Consider making the thin strips that lead from the edges to the wheel axles a bit thicker, perhaps like a filled-in "X" or hourglass shape instead of an "I".

We used a similar system of 80/20 in 2009 and it worked out very well.

I also like the concept of using the strength and stiffness of the bumpers as a structural element. Some spots for mounting them would be wise.

[steelerborn]

Looks cool

We used a similar design for Overdrive
in fact we used the same middle wheels
it worked out well
it would be great for contacts

We are working on somethig for contacts as well

[Joe Ross]

You mentioned cheerleaders lifting it, who's going to be driving it? 8" wheels direct driven from a toughbox is about 14 feet per second. It takes a lot of practice to be able to control a robot at that speed. That doesn't seem wise for a demo robot that is either being driven by inexperienced drivers or driven around people.

[gallo26]

Originally Posted by Joe Ross

You mentioned cheerleaders lifting it, who's going to be driving it? 8" wheels direct driven from a toughbox is about 14 feet per second. It takes a lot of practice to be able to control a robot at that speed. That doesn't seem wise for a demo robot that is either being driven by inexperienced drivers or driven around people.

Well the cheering team would be driving it. So most likely cheerleaders. We're planning on adding gearshifting in the code. So pretty much, 1st gear is 30% motor power, 2nd is 70% power, and 3rd is 100% power. We've done this in the past in competition. and the lower gears are extremely easy to control. The speed is mainly for getting the robot around the field in a timely fashion. Any kind of remot controlled device is going to take time to get used to, so they would hopefully practice.

[joeweber]

Originally Posted by M. Mellott

You plan on using 25-series chain to drive the omnis...how will you tension the chains?

If you layout your sprockets and chain flat on a table you can get the dimensions center to center of the axels and you will not need tensioners. We did this on our test bot and it worked pritty good.

[artdutra04]

Originally Posted by joeweber

If you layout your sprockets and chain flat on a table you can get the dimensions center to center of the axels and you will not need tensioners. We did this on our test bot and it worked pritty good.

Unless you plan on pre-stretching it, 25-pitch chain will "stretch" under a high enough load to the point where it will start skipping. Over very short chain runs (a few inches, max), it often won't be enough of a problem. But over anything longer than a few inches it'll be noticeable enough to cause the chains to pop off.

This past season I experimented with super lightweight floating idlers to much success. The floating idlers I used were polycarbonate sprockets (milled from 1/8" sheet) that were inserted into the roller chain. The tension of them kept them in place. I made several sizes, so that over the course of the competition season the chain could be re-tensioned as it stretched by either moving the sprockets closer to the end sprockets, or by replacing it with a larger idler sprocket.



After our first or second competition, the chain stopped stretching and the sprockets have remained untouched since, where they've lasted through a half dozen competitions. They've worked flawlessly, and have never popped out of the chain or failed in any way, all with a tensioner that weighs a fraction of an ounce.

[kevincrispie]

A robot only really needs a few motors. You could swervedrive it or use tank steering, where you have two motors, one on each side, and them power three wheels on each side if you wanted that many.