Tank tread

[chs1368]

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

[dtengineering]

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

[IndySam]

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.

[chs1368]

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

[A_Reed]

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.

[nparikh]

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.

[Lil' Lavery]

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.

[nparikh]

Originally Posted by Lil' Lavery

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.

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.

[chs1368]

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

[Lil' Lavery]

Originally Posted by chs1368

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

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).

[ChuckDickerson]

Originally Posted by Lil' Lavery

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).

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.

[Lil' Lavery]

Originally Posted by DeepWater

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.

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.

[ChuckDickerson]

Originally Posted by Lil' Lavery

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.

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?

[chs1368]

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

[chs1368]

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