Has 6 wheeled designs surpased tank treads

[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.

[RogerR]

Originally Posted by 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.

maybe you and i don't see the advantage, but apparently they did, else they wouldn't have built it.

but that wasn't the point i was trying to make. i was trying to point out that complexity lies in the design, rather than the type of drive train.

[Wetzel]

116 used a tank design in 99 to climb the puck. It was used again in 2001 to be able to go over the 4x4 but under the bar.


Tank drive was used as a function of the design.
Last year was four wheel drive, with large wheels to get up to the bar. Function of the design.



Stratagy drives design, not features.
Wetzel

[Tytus Gerrish]

small little story:

my legoleague team #2883 competed in a competition with there very complex robot with tank traads. the thing is awesom but it never goes straight no matter what you do and the kids get nervous and due to its complexity they wasted alot of time durring the match in setup.

now they've changed to a 6-wheel drive with the center wheels lowered. and only 1 moterised moving part beyond that a very simple thing. and it GOES STRAIGHT! i think in their next competition they are going to do much better

[Tom Bottiglieri]

Originally Posted by Tytus Gerrish

small little story:

my legoleague team #2883 competed in a competition with there very complex robot with tank traads. the thing is awesom but it never goes straight no matter what you do and the kids get nervous and due to its complexity they wasted alot of time durring the match in setup.

now they've changed to a 6-wheel drive with the center wheels lowered. and only 1 moterised moving part beyond that a very simple thing. and it GOES STRAIGHT! i think in their next competition they are going to do much better

As has been stated before, designs are just as complicated and efficient as you make them. In my teams case, we have been successful with treads. Other teams have been successful with 6 wheel drive.. I dont believe either one is "better".

Tytus brings up a good point.. In his Lego league team's undertakings, 6 wheel drive has been superior to the treads. This is not because treads are a horrible idea and 6 wheel drive is much better, it is simply because that teams design and method of construction may have been different from that which would make "the perect system"

[greencactus3]

Originally Posted by Tom Bottiglieri

As has been stated before, designs are just as complicated and efficient as you make them. In my teams case, we have been successful with treads. Other teams have been successful with 6 wheel drive. I dont believe either one is "better". Tytus brings up a good point. In his Lego league team's undertakings, 6 wheel drive has been superior to the treads. This is not because treads are a horrible idea and 6 wheel drive is much better, it is simply because that teams design and method of construction may have been flawed.

and also in the case of lego, most tires you would want to use have flat surfaces. the rubber lego tread has a taper (is that what you call it?) on the sides, so it will turn better on carpet but on hard surfaces will not help the tread stay flat to the floor. the some lego tires are wide too. which have more scrub when turning so helps keep the robot move in a straight line.

[crazykid234]

This year team 234 used the tank design mostly because it allowed us to fly over the six in. steps. again, the game dictates the design.

[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?