Has 6 wheeled designs surpased tank treads

[Andrew Schuetze]

I am a fan of six wheeled bots and have been reading the lengthy post here on that topic. I am a fan becuase our team can afford to add a third wheel to each side without the need for a lot of extra engineering. Many of my students however are still fans of tank treads. We have never gone that way, we've only had four or two wheeled bot, because of the expense of pulleys, buying extra timing belts for treads...

My question is, How many teams still design and use tank treads on a competition robot What advantages do you think you have over the latests trend of six wheel robots I still don't see us going with treads and this is a general curiosity of mine.


APS

[Arefin Bari]

Hello Mr. Schuetze,

I have seen a lot of 6 wheeled robot and tank thread ones for the past 4 years. both of them are effective. but if i was given a chance i would go with threads, just because of my experience. In reality, tank thread bots has a lot of traction and at the same time, no turning problem.

if you do need to know about tank threads my suggestion would be Contact few teams who has done it for a while. For example, S.P.A.M., Cyber Blue. You can sort their members out on cd by going into the member sectioin and doing an advance search with their team number. good luck...

[Al Skierkiewicz]

Andrew,
If you ever saw the current demand of a tank tread turning on carpet, you wouldn't even think of using it. You can't beat the traction moving forward or back but you will eat a battery trying to turn in a single match. Those that work have some method of raising the track so only a small portion is in contact during turns. Even four wheel and six wheel drives suffer from high current demands unless they employ some method of raising some wheels in turns or use omni wheels on some of the wheels (i.e. front wheels).
If you were to tell me that in driving your robot draws less then forty amps total current but you wonder why your battery runs dead in less than two minutes, I would be able to tell you are using tank drive without ever having seen your robot.

[Arefin Bari]

Originally Posted by Al Skierkiewicz

Andrew,
If you ever saw the current demand of a tank tread turning on carpet, you wouldn't even think of using it. You can't beat the traction moving forward or back but you will eat a battery trying to turn in a single match. Those that work have some method of raising the track so only a small portion is in contact during turns. Even four wheel and six wheel drives suffer from high current demands unless they employ some method of raising some wheels in turns or use omni wheels on some of the wheels (i.e. front wheels).
If you were to tell me that in driving your robot draws less then forty amps total current but you wonder why your battery runs dead in less than two minutes, I would be able to tell you are using tank drive without ever having seen your robot.

I have always had this question, it always looks like that a robot with tankthreads on turns so much easier and this past season i have seen teams struggling to turn with wheels on. How is it that the robot looks like its turning to easily and according to Mr. Skierkiewicz when the robot turns (which has threads on) drains battery? I know our battery used to drain very fast every match. I have never worked on a tankthread system before. any advice will be appreciated... thanks.

[jimfortytwo]

One of the most interesting things I saw at nationals last year was a compromise. There were a few teams who ran 6 wheel drive robots, but each wheel had a notch in it to accept a timing belt loop, on each side of the robot one loop ran around all three tires. During normal operation I image the current leaching effect of tank treads wasn't a problem because the treads barely touched thr ground, but when climbing stairs these robots worked as well as ones with a full set of treads.

[Corey Balint]

^That would be us, team 25. The treads i personally think were only good for getting up onto the ramp, and were basically pointless and more of a hassle during the matches. If you use the same design that we had this year, make sure you give the treads enough room to move around in. Whenever we took a good solid hit this year, the treads would pop off, and be near useless in helping us move. One round they actually completely prevented us from moving. They also were a problem when hanging, if they came off, we might touch the ground and i would have to get them tangled in the wheels in order for them to not touch.

We are definitely going back to just 6 wheels next year, and would probably never think of using the same set up as last years, unless the game required it. If you can improve upon what we had this year go ahead, but from my personal experience it is pretty darn rough. My suggestion is convince your team on the 6 tire set-up, and if you want any help, contact team 25 members, we have had some good experience with it.

[Tom Bottiglieri]

We've been using tank treads for about 5 years now, and we plan to continue using them as long as possible. There is no competetion when it comes to traction.

As stated above, many teams have trouble turning with tank treads. This is because instead of 1" of non sticky rubber material per wheel touching the ground, there is 30+ inches of very sticky rubber touching the ground on each tread. We have used a system of idlers with our treads to overcome this. If you look at the picture below from our 2003 bot, you can see how in the middle of the tread there is an idler which lowers the tread about 1/2" from where the hubs would normally touch the ground. If you balance the weight on your bot the right way, you can cut down the surface area of the tread on the carpet from 30" to 1 1/2"



There are many pros to using a system like this. Because of the idlers, the current required to turn is cut down by a large amount. Also, you can turn "on a dime". But my favorite part of the whole system is when you are trying to pull or push something.. it forces the bot to rotate backwards on the idler, and you can put the entire power of your transmission into the pushing/pulling match. (This is much like putting sand bags in the bed of a pickup truck to increase traction.)

If you are interested in this, I am willing and glad to post pictures and diagrams of this system that has worked so well for us.

[Ben.V.293]

Originally Posted by Tom Bottiglieri

We've been using tank treads for about 5 years now, and we plan to continue using them as long as possible. There is no competetion when it comes to traction.

As stated above, many teams have trouble turning with tank treads. This is because instead of 1" of non sticky rubber material per wheel touching the ground, there is 30+ inches of very sticky rubber touching the ground on each tread. We have used a system of idlers with our treads to overcome this. If you look at the picture below from our 2003 bot, you can see how in the middle of the tread there is an idler which lowers the tread about 1/2" from where the hubs would normally touch the ground. If you balance the weight on your bot the right way, you can cut down the surface area of the tread on the carpet from 30" to 1 1/2"



There are many pros to using a system like this. Because of the idlers, the current required to turn is cut down by a large amount. Also, you can turn "on a dime". But my favorite part of the whole system is when you are trying to pull or push something.. it forces the bot to rotate backwards on the idler, and you can put the entire power of your transmission into the pushing/pulling match. (This is much like putting sand bags in the bed of a pickup truck to increase traction.)

If you are interested in this, I am willing and glad to post pictures and diagrams of this system that has worked so well for us.

I love to see some more pictures of those treads. They look really impresive. What width belts do you use? are they from Brecoflex?

Thanks,
Ben Van Selous

[Warren Boudreau]

With the advent of pneumatic tires in the competition, wheeled robots are now competitive with treaded designs when it comes to traction. I say competitive, not superior. Some timing belt backings can deliver a coefficient of traction of 2.0. That means the pulling force is twice the weight of the robot. I know that this is true because we measured it many times with our highest traction robot, Fluffy. They are competitive because they are more simple to design and build.

As you may have noticed in the past years, those teams with pneumatic tires have a hard time (harder than properly designed treaded systems) turning. The 4-wheel drive systems bounce around like Mexican jumping beans. It is quite fun to watch.

The trick to making any high traction configuration turn is to have what we have termed a "boogie" wheel midway between the front and back rollers on the treaded system. This boogie wheel is a little bit lower than the front and rear rollers. What this does is roughly cut you turning moments in half since you are supporting the robot on the boogie wheel and either the front or rear roller. In a 6-wheel configuration, just lower your center wheel a little bit.

Therefore, I would say, no 6-wheeled designs have not surpassed tank treads in terms of traction. But they can give them a good run.

[Tom Bottiglieri]

Originally Posted by Ben.V.293

I love to see some more pictures of those treads. They look really impresive. What width belts do you use? are they from Brecoflex?

Thanks,
Ben Van Selous

I dont think I have any good pictures of them on my computer, so I will take some at the next team meeting on Tuesday and post them then.

[colt527]

I would have to say that 6 wheel drive systems are much better for rookie to intermediately skilled teams for many reasons. The first being that 6 wheel drive systems are much easier to design and build. For a efficient 6 wheel drive system, you don't need any complex tools. All 3 six wheel drive robots were built on a low budget, with only a band saw and drills. You don't need complex custom made mounting brackets displayed in Tom Bottiglieri's picture that look like it was made with a CNC Milling machine. The design of a good six wheel drive system is a very open-ended one. You can easily design a simple 6 wheel drive system on your first try that may weight a considerable amount or have other draw backs but over the years you will figure out ways to cut weight and increase efficiency.

Treads can probably give better traction in pushing situations and although I have no experience with them, there are probably many other pros to treads.

So, I guess it depends on the contest it self and the experience/tools/budget of the team and neither are superior to the other.

[Pat Roche]

Historically 134 has used tracks most years. We've worked with two diffrent situations with tracks.

In 2004 we used a tread that spanned the length of the bot. Due to the placement of the center of mass and the raised center wheel we were able to turn like a bot with two wheels in the center. This allowed use tremendous pushing power while also allowing us to turn on a dime...literally. We also never had much of a problem with the batteries (granted we only drove with CIMS). We would start a match with 12-13v and never ended with less then 11v. We also never snapped a belt either in 1 regional and three offseason competitions with this drive train.

The second solution that we have attempted is similar to the old German half track. About half the length of the robot would be track and the other side (or if centered both sides) would have casters. This worked well but was not efficient as the 2004 machine.

I prefer the track drive if its designed right.

-Pat

[RogerR]

Originally Posted by colt527

I would have to say that 6 wheel drive systems are much better for rookie to intermediately skilled teams for many reasons. The first being that 6 wheel drive systems are much easier to design and build. For a efficient 6 wheel drive system, you don't need any complex tools....

psst...don't tell these guys that treads require complex tools...



the truth is that a 'bot is only as complicated as you make it. granted, it may be easier to over-complicate a tank-bot, if you design with simplicity and machinability in mind, i expect it could be built with band-saws and drills.

[sanddrag]

In the above robot, what advantage does that have over a good wheel? It is a nice attempt but I don't see the benefit.

[artic_raven]

i have a question about the idlers. about how much lower should the idlers be so that they keep a high efficiency but also don't draw all the current?