Quad- 1/2 track drive system
 

Dr. Johnson and everyone else,

What do you think of this drive system:

Robot oriented such that the 36" side is front, and 30" is side. This is to dampen effects of scrub.

A drive system consisting of 4 small tank treads. (perhaps 4-5 inches each), spaced apart to spread weight and traction evenly.


Each tread being drive by a motor (2 chiaphua, 2 drill),
Each small tread has a driven sprocket, and three idlers on the ground (resembling a triangle)

Each small tread has a center idler which is slightly lower than the other two, creating a "digging in" effect on each tread, gripping the carpet.

The treads themselves could be either brecoflex timing belts (high-end double sided with gripping pattern) , or custom tracks (a la Technokats).

4 motors could be replaced by the 2 chiaphua's.

Programming could be used to account for high amps, if we were rammed, and dull the ampage spike. (True or false??)

The pros of this drive: high traction, lower scrub (than full treads) Increased speed (than full treads), whuile still getting the traction that treads would produce.

What does anyone here think of this? I'm interested in getting opinions from the folks who know.

Would 4 motors cause a major battery/breaker problem?? Any ways to compensate??

Don't spare the criticism, or foresight to any problems you might expect to occur, I'm thinking about this design for next year (its a little late now). I thought I'd ask the folks who know what they're doing.

Thanks for your imput,

--Ben Mitchell

you can get jsut as much traction from four wheels as tread....this is because the weight distribution...if you distribute weight ona smaller area it has more traction....but f you spread it out..like on a tank tread...you decrease your traction...

I think i might be confusing with friction..but traction is friction...

Can an engineer check me on that..or am I way off:confused:

I don't think you'll gain anything other than complexity by going with 4 smaller tracks instead of 2 tracks running the length of the machine. Most of the turn-slip in a tank-style track occurs at the corners, which is just where you have your tracks.

We had a somewhat similar concept, with one caveat. Instead of empty space in the middle, we had two wheels. The wheels were slightly lower than the treads at the corners. It might be hard to visualize, but if you were looking at a side-profile of the machine, you'd see a short track at the front, a wheel at the center, slightly lower than the track, and a short track at the rear. We were pretty confident in this design as a power machine, but we've gone the way of speed so we ditched the treads and went with center-drive only.

Weight in the corners is the problem not the length of the track, as others have pointed out.

You will gain by having your machine wide & short rather than narrow and long, but will it be enough? Difficult to say. Having 4 big watt motors rather than 2 will help muscle through the scrubbing but again, it is difficult to say how much you are giving up.

As to voltage spikes when rammed, they are so far down my list of problems, I don't even think about them. Your machine breaking is more of a threat than electical damage.

Sorry I can't be of more help.

Joe J.

4 wheels have the same traction as 4 treads??? No way!

Would'nt having 4 tracks dampen the scrub issue, or would it be so little a gain as to render the entire concept useless?

What if the drive was modified to a simpler 1/2 track deisign, 1/2 tracks in back, wheels in front? Would that be better in terms of scrub/traction.

Also, would treads and wheels be much faster than 4 1/4 tracks, or would having treads in any combination cut out the speed factor??

What if the quarter-tracks were shortend to 2-3 inches, making them basically the size of wheels, but with the traction of treads.

Thanks for the help.

--Ben Mitchell

We have run with track systems for the past 8 years. The best way we found out is having the track the 36" long. Putting a center wheel in that can move up or down depending on the traction. Get different track that have different friction factors.

We have had fast robots and power robots. we always used two drill motors to run the system. Blowing breaks is a problem if your driver does not know how to drive. With a good driver you can go 2 mins under big loads without breaking the breakers.

This year is great because we added more motors to the drivetrain.

with track system done right nobody will pull you sidewards. once you get what you want you just need to be 90 degrees to your puller.

pulling three goals with 3 130lb kids in the middle is easy done with this track system.


I still think track system done right can not be touched with Wheelchair wheels.

Wheelchair wheels are not the only legal wheels a team can have.

Traction is the thing in my mind, not tracks vs. wheels.

Joe J.

Everything has to be wheels or treads, wheels or treads.....

So what about the other guys? Maybe there's something else out there...*wink wink*

i think there's a good change we may see something totally different this year. it could be us, i just can't tell. you'll have to wait and see:D :p

Shoot, I'll go on and tell you a little right now....

That is, look for team 401!!!! Yeah, we don't have a "traditional" drive train.

So would 4 1/4 tracks be a waste of time?? Would 2 full-length tracks be better in terms power/effort convervation.

My idea is basically replace wheels wityh treads, gaining the traction of treads, and with less material on the ground, have less scrub and more speed (as with wheel)

I am seeking a medium between a tank and a humvee,

Am I wasting my time, or is the 1/4 half-track idea worth pursuing (or at least trying out) ??

As always, opinions on this idea are welcome.

--Ben Mitchell

Um, i think tracks would be better if...
 

Wouldnt' tracks be better if you are dealing with some high-forces on wheels. Where you would eather sink-in too much (than you are carying too much weight!) or wouldn't your coefficent of friction become so much that wheels won't do it? Wheels just place the weight on a point, while tracks place it over a distance. So, in my opnion (sp?) if you some how can "tilt" the goals to get more traction, i say go with tracks. They turn on a dime, and i personally like the experience with them. My team (#5) got feather weight in the finals 3 (?) at GLR, when everyone thought we broke our bar hanging-mechanisim and we didn't hahahaha :), we weighed like 105 or something lbs, and we where pushing bigger, taller, very much heavier robots than us. I say go w/ tanks cuz' of my personal experience with it, and i think the motors will like it better when going straight, especially with a gear-box!!

Word of warning. Tread are very hard to engineer properly. If built wrong, very bad things can happen. Stalling, breaking curcuits. Fun stuff. Like I said before, ours aren't exactly traditional treads or tracks. We like to think, "ouside the box."

Yes, i agree!
 

Yes, 401Mentor, if you don't design the tracks correctly, you will slip the belts, eating them up and they are very, very expensive. And we did have a prob last year with our heavier robot with the treads slipping and poping breakers while turning in high gear...

Basically, with treads, you have more surface area of contact.

So what would that do to you? Well, you have more surface area to take advantage of frictional force, and you won't be pushing as hard on each square inch of carpet your robot drive on.

I don't think using treads will necessary give you more traction. I think this because I believe if you wrap the same tread material around wheels, you will get the same traction.

Say team 45's chain tread with metal pieces digging into the ground, and team 159's wheels with similar metal pieces attach all around the wheel digging into the ground. I don't think there is a lot of difference.

As for being pushed on the side, you do have more side area on your treads to resist against the push, but the resistance should be the same with wheels with similar material wrap around them. With the same pushing force from another robot, that pushing force will spread through out the tread, or concentrate on the 4 wheels. Tread have more surface area to resist, but less force per surface area... Wheels have fewer surfaces to resist, but more force per surface area... They should both come out to be the same...

So, do treads give out a false sense of more traction, because in general the material for treads has better coefficient of friction than normal wheels?

Or, is there some special physics behind treads that help it gain traction over wheels with the same material wrap around it?


By the way, I also believe that it is more important to think about traction and friction of the material you use, rather than thinking about wheels vs. treads.