Tank tread
 

Hello, I am from Countryside High school, Clearwater Florida, near Tampa, Team 1368. We are a rookie team and have only gone to nationals a once or twice. Year after year we have been using chain drive system that has been included in the kit, and last year it broke down almost every single game causing us to end up being 83rd out of 88th in the Orlando regional. This year we are experimenting with new drive systems, we have already designed a few systems already including a tank tread design. As we have never used a tank tread design before its difficult to figure out what type to use for the actual tread, i found from browsing through your website that you recommend BRECOflex timing belts, when i arrived at that website i found many types of timing belts and i was hoping maybe you could help me pick out a good style.

Any help will be appreciated.

Thank you

-Team 1368

Re: Tank tread
 

I expect others will respond with regard to the specific brecoflex treads they have used. While I encourage you to investigate the use of treads as an alternative -- they offer many opportunites -- I would suggest that reliability compared to a properly designed chain/wheel drive system might not be one of them.

While it is indeed frustrating to have chains come off in competition, that is an exceedingly rare event if the chains are properly tensioned and the sprockets are properly mounted. I believe there are some powerpoint presentations in this regard on the FIRST web site. http://www.usfirst.org/community/frc...t.aspx?id=1108 might be a good place to start. I suspect you will find belts/treads to be at least as challenging as chain to align properly and get a reliable drive system.

That's not to say you shouldn't investigate treads... go for it... but consider that the vast majority of teams have chains and sprockets similar to those in the KOP and they work very reliably.

Jason

Re: Tank tread
 

Tank drives are very cool but I wouldn't try to build one in a six week period from scratch. The teams that are successful with these have spent many hours in R&D.

Stick with the tried and true but be careful with the execution. Chain and wheels are simple and near bulletproof when done correctly.

Take next summer and fall and experiment with the tank tracks.

Re: Tank tread
 

well we have already got the design down, we were just wondering what treads to use

Re: Tank tread
 

Team 48 has used treads 2 out of the last 3 years and we have had allot of success with them. If tensioned properly and if you have a lowered center point to reduce skidding and increase turning they should never fall off and they will rarely break. we have used the same style twice now and it works well, it ts the TK10-K13 pulley style with the self aligning groove,and the TK10-K13 Belt profile to match. we have also used two different backing materials, in 2004 when there were slick plastic topped platforms to climb onto we used a Linatex (Red) backing, in 2006 when it was mostly carpet we used the supergrip (Green or Blue) backing to dig into the carpet.

http://www.brecoflex.com/?CATID=1&SC...ENID=22&BMID=2

http://http://www.brecoflex.com/?CATID=1&SCATID=6&SMENID=22&BMID=5

http://www.brecoflex.com/?CATID=1&SC...NID=11&PURA=21

*Do only if you have the time*
we have also transfered our tread system from 2004 to 2006 in form of a module, for ease of replacement of broken treads.

Re: Tank tread
 

Just a point of inquiry:

Why not use just a 6 wheel tank DRIVE, but without the treads? We've (25) been doing that for the past couple of years and have met with very pleasant results. The problem with treads is that they're really unnecessary unless you're climbing some kind of stairs or what not. I've seen many teams with tank treads get pushed sideways and then end up burning up and/or tearing their treads to shreds --leaving much to be fixed.

Re: Tank tread
 

I'm curious as to how the KoP drive failed last year. It is one of the most reliable drive-trains available, when properly constructed. It may not have the speed or flashiness of a shifting transmission, the agility of an omni-drive, or the contact area of treads, but it definitely works.
A properly constructed tread system is usually very reliable as well (but even the some of best teams have sometimes had trouble with belts snapping). That said, any issues that arise are often worse in belt drives than chain. For example, it's far harder to change the length of a belt than it is the length of a chain if the sprockets are positioned wrong, etc.
If you feel a tread drive is the best solution for your design, and you feel confident about building it, go ahead. But I just give you my cautions that they are no easier to build than the KoP drive system.

Re: Tank tread
 

I absolutely agree. By the way, you said you have a design done--but have you built a prototype? Just a piece of advice since we've been doing this a while--oftentimes we'll design something that seems so perfect--and realize 1/2 way through that it won't work--or isn't feasible in our time frame, budget, etc.

If you do decide to go with a tread system, make sure you have plenty of extra belts as you'll probably be needing them. Like Sean said, just take care in making such a decision.

Re: Tank tread
 

our chains broke quite a bit last year, we dont how, but it might be the tension i believe.

But right now our team is split into 3 design team, 1 is for tank tread, 1 is for a 4 wheel drive system (with each wheel having its own gear box) and 1 for another design we like to call the omni drive design, I am currently working on both the tank tread and omni Drive. ive included a picture of my omni drive design, not the greatest in detail or any dimentions, but its something just to go on
the motors attached to the drive wheels are the really big ones which you were only allowed 2 of and the ones attached to the omni wheels are the smaller ones

Re: Tank tread
 

I'm curious to why you would use asymetric motor placement in a holonomic system like that. Also, I'm curious as to why you chose weaker motors for the "drive wheels" (even though the CIM Mini-bike motors are larger than the regular CIM motors, the regular are actually a more powerful motor).

Re: Tank tread
 

Actually, I was curious why one would put any motors on the omni wheels at all. In the pictured design they are actually only used for balance and could not move the robot sideways anyway since the drive wheels do not appear to be omni so why power them at all? The robot can simply turn like a two wheel differential drive but not actually move omni-directionally in a true holonomic sense.

Re: Tank tread
 

Unless their drive wheels have a tremendous amount of traction, if both "omni-wheels" are powered in the same direction, the robot would move that way, regardless of the "Drive wheels" not having rollers. It would just be a less efficient holonomic drive.

Re: Tank tread
 

Maybe but I find it hard to believe that the two omni wheels (driven in the same direction) would have enough traction to overcome any "decent" traction wheel. Maybe 2 AndyMark Omnis vs. 2 of the KoP Skyway wheelchair wheels but then wouldn't it just be much more efficient to just use 4 omni wheels?

Re: Tank tread
 

the reason i put motors on the omni wheels is that if were stationary and turning we could turn a lot faster, also this would allow us to turn while we were in motion (like moving forwards) another is say for last years game if we had a stationary turret to shoot those balls, we could make precise adjustments to where our robot was facing

and thank you lavery for telling me that the regular motors are more powerful, i did not know that

Re: Tank tread
 

also why we dont put omni wheels on for the drive wheels is that we feel we could get pushed around very easily

Re: Tank tread
 

Omni-wheels (theoretically) have no less traction in their "Y axis" (forward/reverse) than regular wheels do, so they would have the same slippage point as the drive wheels. In practice this is not always true (particularly with traction wheels and omni-wheels with plastic rollers), but with the right wheels it could be. Say they use AM Trick Wheels with the black EDPM rubber rollers and lower traction drive wheels.

Re: Tank tread
 

but if we get hit from the side, if we have 4 omni wheels, we're gonna move in the direction we're hit in

Re: Tank tread
 

you said the extra motors (on the omni wheels) were so you could turn faster but a 2 wheel drive setup will turn very quickly whether you have 2 un-powered omni wheels or ball casters and i am not sure you would be able to make more precise turning with them unless they were geared to drive slower

Re: Tank tread
 

The whole point of an omni-directional drive train is that you can out maneuver a pusher type robot like a tank tread, 4WD, 6WD, 8WD, etc. so you never have to worry about getting pushed around. A non-omni directional robot (typical FIRST type 4WD, 6WD, tank tread, etc.) is designed to push it's way around but will not usually be as maneuverable as an omni robot. I think you are trying to do both but in doing so you may not succeed in doing either very effectively. My suggestion is to think about two separate designs (one made for maneuverability and one for pushing) and then on Saturday decide what your game strategy will be and go with whichever design you feel will best match your game strategy.

Re: Tank tread
 

one more note on treads : if they are properly tensioned(not overly tight and not loose) they can be very reliable. in 2006 we only broke only one tread, any other replacements were do to wear over the two previous regionals, compare that to 2004 when we snapped 4 over three regionals and nationals on account of losing tension in the middle of a match.

Re: Tank tread
 

Hey guys, ive read all your posts and i have to say alot of you have great arguments for your reasoning, and i agree with most of you. Everythign in the end comes down to the game and the history of design of the teams you will be opposing at regional events. For team 1368 i suggest analyzing the game as well as the opponents then decide what you want to do, also as for belt drives the friction force of the belt on the pulley is less than the force put out by a pushing robot, so if you get hit and pushed, you WILL get pushed and your belt system WILL slip on the pullies. Also i suggest a simple rocker drive system with powered wheels in the center powered by CHAINS with 2 omnies on at the sides of the robot, this configuration works best.

Re: Tank tread
 

With Splined(Toothed) pulleys,from brecoflex, you will not get pushed from the front and with the correct belt profile(V shaped profile in the center, TK10-K13) your belts will never slip sideways, this mixed with the long contact patch basically means you won't get pushed sideways either. the only pushing weakness of treads is due to your gearbox, if you don't have enough torque you will get pushed front to back or if the opponent catches a corner of your robot you can be spun.

Re: Tank tread
 

There seems to be a mix up, i meant that the belts will lose grip on the pullies they are driving and will slip on them, even if the belt is toothed, there will be a point where it is stretched out a little bit from use and will no longer grab on to the pulley like it used to, then it will slip on the pulley.

Re: Tank tread
 

Track drive / tank treads have there good points and bad.
On a light unit the tracks will tend to come off the idler wheels... and they will be a lot of adjusting to make them work right. They great for climbing ramps and pushing other bots out of your way (if you got the motor and gearing for it) but other than that there just a headache.
I think speed gonna be needed for this game... wheels the answer.

Re: Tank tread
 

Hey, just some quick insight if u do decide to use a tred system. I am on team 288 and we have been using treds for the past 7 or 8 years and it takes ton of time to get everything to work properly. If you still decide it will take a long time which will take away from the other problems you'l face like scoring. It took us 3-4 years including the off season to perfect it. If you can get it to work efficeintly in 6 weeks... you eather were lucky or very smart people. :)

Re: Tank tread
 

team 61 has been doing tracks for over 10 years and we stop due to Breco flex could not make us a belt that would not rip. the power we where using where ripping the belt. at $340 a belt we went with wheel last year. Had some good results. Track are great and are better than wheels only if you can keep them from breaking. the power that is given to us now is way to much for the Breco flex belts.


we go with 6 wheel system almost the same results as a tank drive system

if you want to see the tracks go to our web site

http://www.valleytech.k12.ma.us/robo...photos2004.htm

Re: Tank tread
 

if you are going to use a tank tread desing you mite want to keep in mind that it is very hard to ketp a tank tread on with out giving it tooo much slack. also im couries on how you plan to trun your robot.

kyle from (team 1094)

Re: Tank tread
 

If your Robot is made correctly, and centered in it's weight the robot should have no problem turning around in a 360 degree....