04-10-2009 23:18

Akash Rastogi

Re: pic: 6 Wheel Drivetrain

Before anyone flips about the pocketing on this...

Note that this is for sponsored robots, not for competition use. IE: t shirt launchers

04-10-2009 23:23

Nick Lawrence

Re: pic: 6 Wheel Drivetrain

Looks like fun.

Even with it not being a competition robot, I'd still be a little worried on the pocketing. Would having a little less of it be out of question?

-Nick

04-10-2009 23:28

gallo26

Re: pic: 6 Wheel Drivetrain

Each frame will have its own paneling to cover everything up.

04-10-2009 23:39

AdamHeard

Re: pic: 6 Wheel Drivetrain

The fact that it's not for comp is even more reason not to pocket it.

Just leave the 1/4" plate solid, it'll be stronger, prettier, and waaaaaaaaaaay quicker to manufacture. It will also make the base more stable for whatever it's being used for.

04-10-2009 23:44

gburlison

Re: pic: 6 Wheel Drivetrain

6 wheel drive and all that pocketing seems like a lot of work for a non-competition robot.

04-10-2009 23:49

gallo26

Re: pic: 6 Wheel Drivetrain

I didn't want to leave it solid. It will be covered by bumpers and the perimeter will be lined with .5" square tubing. The looks of it won't matter, and in my opinion pockets make it look pretty neat. But that's besides the point...

I do agree that the holes for the wheels need more beef. It is .5" width now, I should have put it as .75" width. The rest of it is identical to the plate we used for our 2009 bot. Its just a foot longer.

04-10-2009 23:52

rsisk

Re: pic: 6 Wheel Drivetrain

Can someone explain what "pocketing" is?

Thanks

04-10-2009 23:53

R.C.

Re: pic: 6 Wheel Drivetrain

Pocketing is pretty much "how" much material you take out of a solid piece. Pretty much also the CNC cutouts of a piece.

Also on CAM programs, pocketing is an option for type of toolpath.

-RC

05-10-2009 01:10

James Tonthat

Re: pic: 6 Wheel Drivetrain

Maybe higher ground clearance. If its noncompetition, I can see it going around sidewalks, pavements and grassy areas.

05-10-2009 02:42

M. Mellott

Re: pic: 6 Wheel Drivetrain

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.

With 8" wheels and a 5"-wide plate (assuming wheel centers are in the center of the plate--at least it looks that way) gives you a 1.5" ground clearance? Should be OK.

I have to agree with others that you need more meat on the side plates...1" on the webs at least, and big radii in the corners of the pockets. Always start with a strong base, even if it's not for competition.

80/20 is good stuff, but you have to watch that the bolts holding the frame together don't come loose--they always seem to eventually. If you're not going to take it apart, you may want to consider Lok-tite (or tack welds).

All that said, it looks like a solid, simple design that should go together very quickly.

05-10-2009 09:32

Tom Line

Re: pic: 6 Wheel Drivetrain

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.

05-10-2009 10:19

Jeff 801

Re: pic: 6 Wheel Drivetrain

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.

05-10-2009 10:31

artdutra04

Re: pic: 6 Wheel Drivetrain

A piece of .030 to .062 polycarbonate will do the same thing for less weight.

05-10-2009 10:36

Chris is me

Re: pic: 6 Wheel Drivetrain

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.

05-10-2009 12:21

gallo26

Re: pic: 6 Wheel Drivetrain

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.


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

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!


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

05-10-2009 16:55

AdamHeard

Re: pic: 6 Wheel Drivetrain

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.

05-10-2009 20:47

cdebo

Re: pic: 6 Wheel Drivetrain

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.

05-10-2009 21:01

R.C.

Re: pic: 6 Wheel Drivetrain

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

05-10-2009 22:28

gallo26

Re: pic: 6 Wheel Drivetrain

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.

05-10-2009 22:50

DonRotolo

Re: pic: 6 Wheel Drivetrain

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.

06-10-2009 00:25

steelerborn

Re: pic: 6 Wheel Drivetrain

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

06-10-2009 09:19

Joe Ross

Re: pic: 6 Wheel Drivetrain

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.

06-10-2009 12:14

gallo26

Re: pic: 6 Wheel Drivetrain

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.

10-10-2009 21:39

joeweber

Re: pic: 6 Wheel Drivetrain

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.

11-10-2009 00:54

artdutra04

Re: pic: 6 Wheel Drivetrain

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.

30-10-2009 21:09

kevincrispie

Re: pic: 6 Wheel Drivetrain

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.