Tank tread

[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?

[Lil' Lavery]

Originally Posted by DeepWater

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?

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.

[chs1368]

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

[ChuckDickerson]

Originally Posted by chs1368

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

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.

[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

[A_Reed]

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.

[eshteyn]

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.

[A_Reed]

Originally Posted by eshteyn

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.

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.

[eshteyn]

Originally Posted by A_Reed

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.

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.