Ive been watching alot of video’s from previous years and reading alot of white sheets.
Things I have figured out:
Tread is inneficient (at least compared to wheels)
Wheels have less traction.
Now while I know those are horribly obvious they help me with my question.
Especially in last years video’s I noticed traction being a big issue. (Teams trying to push both goals up the ramp had a hard time.
Now I know we dont know the game yet. But I still ask the question. What do you guys think of as the pro’s and con’s of both systems? Does anyone swear by either one regardless of the situation? With carpet is something like the tiger cats robot from last year with those awseome metal grips on the bottom worth it? has anyone done anything like that to the wheel chair wheels?
have you ever seen the Technokats (45) treads? they had the most efficient and fastest drive systems out there. those things could plow over anything they wanted to. motor setup that they had didn’t hurt them at all. i’ll let andy, kit, clark, or dj explain it better because it was thier robot.
Copying the Techno-Kat tread setup is not for the faint of heart. I really would not advise a rookie team to start there.
It is very labor intensive. Each aluminum cleat is hand made and I’m pretty sure that steel mounting brackets must be made and welded onto the chain for each cleat.
In general, I would say that treaded systems are more difficult to debug and maintain. #45 has made it work wonderfully for them, but I would advise that your 1st robot have a simple 4WD, tank steering setup. It will be easier to build and you’ll have a lot more time to debug it.
The traction problem that many wheeled machines had last year stemmed more from the relatively low friction between the bare wheel chair wheels and the carpet.
I would advise you to invest some time in finding materials that can be wrapped around the wheelchair wheels for increased traction. Many teams, including us, used timing belt material.
If you have good grip with your wheels, there shouldn’t be a problem. Our machine last year could pretty easily push both goals (one loaded with balls) onto the bridge
The TechnoKats have awesome drives. Their method of doing tracks is very efficient — FOR A TRACK.
I disagree with any claims that they are as efficient as wheels.
More than that, they use the drill transmions. This is a very fine transmission and it provides a very cool feature (the ability to shift gears) but it is NOT the most efficient transmission by any measure. 2 or 3 planetary stages will give an overall efficiency of about 70 - 80% While this is good for a planetary transmission, the same reduction done with straight spur gears will be in the 80-90% effecient.
More to the point, the decision to go with tracks or wheels is more based on the field and the obstacles than drivetrain efficiency (imho).
For us we wanted alot of grip of course. So what we did was
wrap timing belts around the wheels wit the teeth side out and we had superior traction. Also if you make your own wheels that are real wide, just make them out of plywood, you can get more traction. Another thig I see alot of teams make the mistake of is not balencing the weight of thier orobt evenly over thier wheels. Lik putting all of thier weight over thier 2 back or front wheels and they have thier wheels slipping the whole time.
I just remembered the first time I saw the Techno-Kat kleeted track system in action. I think it was in Yipsilanti the first year they used the system and we were pit neighbors in that god awfull crowded pit area at the new arena.
Anyway I swear that I saw a “Carpet Fiber Rooster-Tail” when that thing screemed across the floor during the first practice round. FIRST must have seen it too given all the filing I saw to those kleets just after the match. Looks as though they have it “dialed-in” now.
One of my fond memories for the past ( memories are hard to come by anymore since I’m getting old)
I’ve got some good pics of the treads on my computer somewhere…i’ll look for them and post them…even though u guys arent on my team you did a pretty darn good job explaining them.
Also if u notice in David’s pics that the treads are actually “curved”, those were an earlier type that were a thinner material…later we changed them to a little bit thicker material so they wouldnt bend like that…
We have used treads with the chain and cleats twice, in '99 and '01. The '99 system, while having very good traction, was not very efficient. The chain and cleats ran in Delrin guides on the bottom of the robot, and while Delrin is a fairly slippery material, there was a lot of power loss. Also, the parts of the frame supporting the idler sprockets were a bit flexible allowing the chains to roll off a few times. All in all, the system served us quite well in the traction-intensive '99 competition.
In 2001, we replaced the “slider” guides on the bottom of the machine with rolling idlers, greatly reducing power loss. Also, Andy’s extruded aluminum frame is very stiff. We never had a chain roll off with this machine. A final new feature which allowed us to use relatively “high” gearing for a tread machine was that we used both a drill motor and a Fisher-Price motor for each side, giving us more horsepower than we had available in the past for our drive train.
Of course, as Joe mentioned, we still use the drill gear boxes which are not as efficient as custom made straight cut spur gears would be. We compromise on that in order to be able to have more time to work on the rest of the robot, and to allow us to build most of the robot in the club shop. To make our gear boxes would require significant “shop time” at one of our Delphi shops.
We mounted steel cleats into our wheels last year and it gave us real good traction. We were able to pull a loaded stretcher over the ramp last year. Our cleats were similar to the TecknoKat cleats and also required a fair bit of hand work. With the cleats you need to be real careful otherwise you can damage the carpet or the playing field. We will probably stick to plain wheels this year unless the game dictates the need for extra traction like last years game.
Okay, time to brag just a little about 122’s drive train. We have four wheel drive and love it. The downside to having four wheel drive usually is turning - wheels have to slip side-to-side and the center of rotation is around the center of the robot. We however, through an incredible amount of labor, made omni-wheels, or regular sized wheels with many smaller lexan wheels that spin side-to-side. The result is that our robot had absolutely no trouble going up the ramp with two loaded goals, but could still turn quickly around its rear wheels. Our rear wheels can then also have as much traction as we can give them, without having to worry about being able to turn. The ridges in the mini-casters also helped a lot in being able to climb up over the wood block under the bar.
~Tom Fairchild~, who’s getting off his high horse now.
We, or actually Mark Koors first came up with the front wheels for our 1998 machine that would slip sideways easily while having good fore and aft traction . We were able to run much “taller” gearing with these wheels than with four wheel chair wheels. We used similar front wheels, but of simplified design in 2000.
Now that we have our track system developed to where it is almost as efficient as a wheel system, we may use it for 2002 even if the game is not particularly “traction intensive.” We’re kind of making the assumption that we will still be playing on carpet. There seems to be a trend regarding the use of carpet for the playing field.
T95 used a 6 wheel drive, where the center wheels were slightly lower down then the fore and aft wheels. This ment that the bot would rock back and forth slightly on the middle wheels when unloaded. All 6 wheels were linked by chain, but when turning the fore and aft wheels would just scrub, since they had relativly little load and traction, while the middle set would hold and do most of the turning.
When going up the ramp the CG would shift and the back and middle sets would be engaged. When moving a goal, the CG would shift even further back and the bot would acutally do a bit of a wheelie on the aft wheels. With two goals carried, it again balenced on mainly the middle set, but the added wieght of the goals gave enough traction to get the job done.
shrug No one ever said you could only do 4 wheels or 2 treads. 6 wheels worked for us, but like treads, its more work and harder to maintain (popping chains were a chronic problem never fully fixed). It’s all dictated by how you plan on playing the game really.
Those side slipping wheels are cool, but just wondering. Did you run into problems with being pushed form the side? or on a sideways incline (I know you shouldnt have been sidewats last year, but it wasnt unheard of)
Just seems that while nice they would allow you to be pushed around alot.
Your 6 wheel drive design with the center wheels a little lower than the front and rear wheels is a good way to make a machine that will turn easily while having good traction.
I suspect that you have learned enough from your machine that if you do another 6 wheel drive machine, the “chain popping” problem will be gone. While I saw your machine, I don’t remember what chain you used, but if you use #35 chain, you should have no problems. It won’t break and is a little tolerant of less than perfect alignment.
*Originally posted by Jordan A. *
**Those side slipping wheels are cool, but just wondering. Did you run into problems with being pushed form the side? or on a sideways incline (I know you shouldnt have been sidewats last year, but it wasnt unheard of)
Just seems that while nice they would allow you to be pushed around alot. **
We used the side slipping wheels on the front of our '98 and '00 machines, and the machines could be pushed sideways more easily than if the machines had wheel chair wheels at both ends. It turned out that not much pushing occurred in the '98 game and most of the pushing was fore and aft in the '00 game. Your point is a good one, though. In a game where robots could be pushed sideways to advantage, the side slip wheels would definitely be a compromise.
I know for the 2000 compeition on 308, we used plexiglass/aluminum sprockets. If you look on the link below, you can sortof see the wheels. (They look blue because it each wheel was 3 layers, 2 plexiglass layers with a aluminum layerin the middle) The reason we made those up was because we could get excellent traction going in forward and reverse, and provide enough side slip so we could turn. The problem we found using the wheel chair wheels in a 4 wheel drive system is they don’t give much side slip, and make it very hard to turn. This puts alot of extra strain on the motors, and would cause them to overheat/burn out. This also put more of a drain on the battery due to the extra amount of work needed to turn the machine.
I know many, many people are going to disagree with me on this one, but I cannot stand wheel chair wheels. When used as drive wheels, they slip easily and more effective wheels can be quickly and cheaply made. When used as casters, they wobble and shake unless extremely well aligned. But, that’s just my personal experience with them. Those of you who do like them, please say why. I’m sure there’s some method to your madness.
~Tom Fairchild~, who wished other wheels came with the materials kit so teams would not be so inclined to use bad traction wheels.
