Treads, Tracks, Tank system Talk/Help

[Mr.Rush]

I am inclined to agree with Void, I've lurked on many a threads about this topic and all too often people assume it will be used for competition. The honest truth as he stated is he never once mentioned competition use, He might have mentioned a design of a universal chassis but that is all.

There have been a few responses that have been made with the honest intentions of help, and there are others who insist on thoughts based entirely on FIRST competition environments. This is a little news flash for some of you there are robots built outside of the little FIRST robotics bubble. I hate to see the witch hunt against free thinkers continue on this little ragtag forum, but it seems that there isn't a genuine desire to think differently

[M. Mellott]

Team 48 has used tank tread drive trains of various designs with great success since '04. As a team that loves to play defense, we utililize the traction and stability that tank treads provide. Examples of our past tank drives:

2004 - triangular design to climb the vertical side of a 6" high platform
2007 - combined with 2-speed transmission, provided superior pushing power
2008 - a year where no one in their right minds would have thought to use treads, we wanted them for stability around the corners while carrying the trackball

As for the issue with turning, we were able to solve that with a couple methods:
- including one or two bogey wheels located under the CG point that could be lowered 1/8" to 1/4"
- instead of full-length treads, use a half-track system with omni wheels, such as our '08 robot shown above. A more typical method is moving the treads to the rear of the robot and a pair of omnis at the front. You maintain your pushing power, but the turning is much smoother.

Also, drivers need to develop "tank steering". With older tanks, you don't often see one turn on the fly--often they drive in a straight line, then stop forward momentum to turn with one tread going in the opposite direction of the other in a zero-radius turn.

For belt tensioning, our shop teacher developed a system that tensions the dead axle of the non-powered outer wheel. This was used in all of our systems and can be seen in the pictures above.

One of the biggest issues we had to deal with was the sheer stress on the belts brought on by side contacts, as our driver liked to interfere with another robot by drivng in front of it perpendicularly. If your robot is pushed from the side, the belt can twist (sometimes right of the tread wheels) or sheer a steel-reinforced belt in half--and that's not pretty when the belts run between $150-300 each. You have to have a system in place that keeps the entire length of the belt in contact with the carpet (or at least at minimum intervals) from sliding sideways, be it with bogey wheels, slider blocks, etc. Keeping the belt in line is critical in a successful tank drive. With a half-track system, we found that the side stress were much less due to the shorter length and extra lateral support was not needed.

Please feel free to PM me about this.

[AdamHeard]

Originally Posted by Mr.Rush

I am inclined to agree with Void, I've lurked on many a threads about this topic and all too often people assume it will be used for competition. The honest truth as he stated is he never once mentioned competition use, He might have mentioned a design of a universal chassis but that is all.

There have been a few responses that have been made with the honest intentions of help, and there are others who insist on thoughts based entirely on FIRST competition environments. This is a little news flash for some of you there are robots built outside of the little FIRST robotics bubble. I hate to see the witch hunt against free thinkers continue on this little ragtag forum, but it seems that there isn't a genuine desire to think differently

If you come to a forum devoted to the FRC competition, and ask for help, people are going to assume it's for the FRC competition. People will then post the best advice they have. This is what happened, you can't blame the people that replied for it. If the original post had said, "Hey, we're just having fun here, this isn't for FRC, help me out with this tank drive", people would not have offered him the good advice for FRC, they would have offered him a different set of good advice for just getting his tracks working.

If I go and post in a forum for battlebots about making a drivetrain and not say it's for FRC, and then get mad when people suggest many things that are contradictory to a FRC drivetrain or not helpful, I really can't get mad at them for that.

[UndergroundVoid]

Originally Posted by AdamHeard

If you come to a forum devoted to the FRC competition, and ask for help, people are going to assume it's for the FRC competition. People will then post the best advice they have. This is what happened, you can't blame the people that replied for it. If the original post had said, "Hey, we're just having fun here, this isn't for FRC, help me out with this tank drive", people would not have offered him the good advice for FRC, they would have offered him a different set of good advice for just getting his tracks working.

If I go and post in a forum for battlebots about making a drivetrain and not say it's for FRC, and then get mad when people suggest many things that are contradictory to a FRC drivetrain or not helpful, I really can't get mad at them for that.

But does that really give a reason to tear an idea apart even if it were to be used for a competition purpose or personal project.


And thanks M. Mellott i will take you up on that offer sometime

[AdamHeard]

Originally Posted by UndergroundVoid

But does that really give a reason to tear an idea apart even if it were to be used for a competition purpose or personal project.


And thanks M. Mellott i will take you up on that offer sometime

Because you didn't indicate otherwise, the masses assumed this would be for FRC competition (as is most of the technical posting on here) and offered some good advice; tanks aren't ideal for the FRC competition. In fact, your original post makes it seem very much like it was for FRC competition. You can't really fault anyone for what they said, they offered good advice.

Now, as a personal project, go ahead, have fun, get it done. They may not be the best choice for a FRC robot, but they sure are cool.

[UndergroundVoid]

Fine what ever you want to think, yes i admit the initial post is very opaque on that. But isn't it unfair for a person to ask a question and get answers that you didn't ask for. i expected help would bring the essence of the word to my questions and not some little post going off on how treads are bad, wheels are good. If i ask what color the sky was and they said 4 or something i would be irritated like i am now.

[Billfred]

Originally Posted by UndergroundVoid

But does that really give a reason to tear an idea apart even if it were to be used for a competition purpose or personal project.

Tear apart? No. However, Adam is right; put a thread in Technical Discussion without some frame of reference to the contrary, and people will default to thinking about FRC applications.

Of the teams I've worked with, only one has ever attempted treads; that would be 1293 in 2007, the first season I was not active with them. Their entry that year, Atlas, had some limitations. Their approach was solid, with the exception of their gearbox mount; the BaneBots gearboxes they used were mounted in the front of the robot using an open-front frame for their grabber. This left their setup particularly exposed to hits, and left them scrambling to move in their last match where they partnered with us. Some might argue it to be too solid; each of their drivetrain pods weighed over ten pounds. (That thread actually has a lot of tread lessons learned; I'll see if I can get a member of the team to offer any further insights here.)

You may also want to read Chris Hibner's paper on drivetrains. Much of it carries over from wheels to treads.

For the side talk about the appropriateness of treads, I say this: I care about whether your robot can successfully execute a strategy that complements our own. Wheels, treads, kiwi, swerve, it doesn't matter; all that matters is that I can rely upon you to execute.

Originally Posted by UndergroundVoid

But isn't it unfair for a person to ask a question and get answers that you didn't ask for. i expected help would bring the essence of the word to my questions and not some little post going off on how treads are bad, wheels are good. If i ask what color the sky was and they said 4 or something i would be irritated like i am now.

If you ask me a question about how to step on a car's gas pedal, I would feel obligated to make sure you were aware of how to step on the brake as well. The ability to relay both sides of an issue is important in any regard.

[Cory]

My advice would be to go look at teams who have done treads well in the past-45, 48, 1114, etc.

You will probably have 2 or 3 big issues to overcome. One is tensioning the belts adequately. Another is making sure that when you get pushed from the side they don't fall off/shear. The last being to make sure that you can actually turn (Drop one of your idler pulleys to reduce your contact patch with the floor).

Another concern is that the belts are VERY expensive. I believe most teams use the steel core heavy duty self tracking Brecoflex belts. They can be $300 EACH. Brecoflex also has a 2-3 week lead time on their belts. In addition many teams have had problems with their belts shearing. I believe some teams have had better luck with FN Sheppard (prices/quality/lead-time).

I personally think that there are very few (nearly zero) situations in which a treaded drive is a better use of resources/more useful for a FRC game than a standard 6WD chassis, but it can be a good learning experience for you and your team.

[UndergroundVoid]

Originally Posted by Billfred

For the side talk about the appropriateness of treads, I say this: I care about whether your robot can successfully execute a strategy that complements our own. Wheels, treads, kiwi, swerve, it doesn't matter; all that matters is that I can rely upon you to execute.

Nicely put Billfred and thanks for the edit but i still have only one thing to say. I never said once if this project was or wasn't for competition. So to put it out there its both. It is how EricH said about having ideas in a goodies bag whether i use them or not it up to my team, but at least i have a plan if we do choose that road or even if i choose that road in my spare time. Also ideas from one systm can be used in other systems. So in result the thread is your you can choose what to do with it since i have gotten enough information and people to help me produce this plan for this road.

[Al Skierkiewicz]

Lynx,
You have to remember that the answers you receive here are tempered by our involvement in FIRST robotics competitions. The advice you receive is aimed at those competitions only. The comps are played on carpet which can be an unforgiving surface for tracked vehicles unless a particular game (and strategy) warrants their use. The picture above and the caption explains it pretty well, "It wreaked havoc on the breakers though you could year them popping clear across the shop". In addition, the type of treads used in this picture would not be allowed under 2008 robot rules as no metal can come in contact with the carpet. The only advantage in this picture is the curved ends of the tread cleats. In a turn, these tend to slide across the carpet while giving increased traction in the forward and reverse modes. I will say it again, treads in a turn or six wheels/no steering, create significant electrical loads that can comprimise the control system electrical power source. As such any good strategy would be to avoid, at all costs, mechanical designs that draw excessive currents. There have been (and likely will in the future be) games and strategies that use treads to a advantage. These games will likely involve climbing with little or no turning required.

[JesseK]

While it is conceivable that the GDC will put a difficult terrain on the field for all robots to traverse, I do not believe it will ever happen. First, rookies still have to have a way to be successful with the bot, hopefully just by driving and pushing something. Otherwise many would be discouraged in their second year.

Then there's the fact that the field itself is already alot to move around when it's just carpet. Volunteering at Battle O' Baltimore 2 and then sticking around for field teardown at the end really opened my eyes to what it takes to create something that's easy to setup. Whoever designed the field is a master of aluminum extrusions. On top of that, there was very little room left in the NASA trailer for additional field elements after the overpasses, electronics, and general field equipment was put in it.

So for tricky terrains -- you can always hope, but I think there will always be a way to not have to deal with it.

[Al Skierkiewicz]

Jesse,
Ramps, stairs and platforms are all field elements that have been used in the past and will be seen in the future. Those are the elements to which I referred.

[Alan Anderson]

Originally Posted by Cory

My advice would be to go look at teams who have done treads well in the past-45, 48, 1114, etc...

The TechnoKats' tank-treaded robot was built long before I became a part of the team. It is one of the few old drivebases we have that still function, but its relevance for current design is very limited. It was made with a major underlying feature: wide metal cleats. It looks a lot like the picture Mr.Rush posted. That helps maintain forward traction while allowing a certain amount of side slippage. It still won't turn without using a lot of power.

In the years I've been with the TechnoKats, we haven't seen a game where we would consider trying tank treads again. They just don't give an advantage over other drive systems. If the field were deeply covered with sand (or corn), they might make sense, and we'd probably apply a lot of thought to how best to design them. But on carpet, or tile, or concrete...nope.


Looking back on the first post, I see an issue I overlooked before. It looks like Lynx has already designed the frame with wheels, and just wants to know a good way to put tank treads on it instead. He probably isn't going to like my saying this, but I don't think a "good way" exists in such a case. Changing from wheels to belt-style treads will likely only make it perform worse.

[Mr.Rush]

Al seems to have misunderstood my post (not the least bit surprised) the breakers were popping wile the chain tension was too high, not when properly adjusted, and at no point did the chain contact the ground the rubber cleats are a hair shy of a half inch in thickness. (its a vintage bot from the '01 game Diabolical Dynamics)

And yet again we have some one jumping to the rule book and its not even build season. I understand that FIRST experience guides your judgment, but if his project is out side of the FIRST bubble then why bring up the rules?

[IKE]

Don't forget one of the most famous tread bot Johny 5.

That robot seemed to move pretty smoothly on a lot of different surface materials and surfaces. (Could be movie magic)

Essentially that machine was a 1/2 track with articulating treads and a rear caster wheel set. It may be worth reviewing those movies just to watch the tread motions and the machines manueverability.