Re: Treads, Tracks, Tank system Talk/Help
 

Nicely put EricH.

Re: Treads, Tracks, Tank system Talk/Help
 

Power depends on the motors and any mechanical losses in the drive system. All else being equal, wheels and tank treads should have no significant difference in pushing or climbing power. Tanks are better at dealing with unstable surfaces, but unless what you're driving on moves or shifts there probably isn't a good reason to use them.

A larger footprint does not have any theoretical advantage in traction. With the same coefficent of friction and the same weight, the amount of surface contact is not a factor.

With carpet deforming more under the concentrated weight of wheels, the actual traction of a FRC robot is somewhat complicated to predict in advance. Experiments seem to show that wider wheels are better in practice than narrower ones, but long tank treads don't give the benefit you attribute to them. On the contrary, the difficulty they create in turning is usually considered to be a good reason to avoid them.

Re: Treads, Tracks, Tank system Talk/Help
 

This is sort of true. With compliant surfaces like carpet, rubber tires and treads there is some degree of mechanical interlock that can change the grip level to normal load.
While you can generally equate a coefficient of friction as a constant, there are noticeable changes relative to load. I think 494 did a neat project on this.
%slip also makes a huge difference.

Any students interested in a good/simple science fair project, this is a solid one. Map the coefficient of friction between two materials (let's say carpet and brown ruff belting) vs. contact area and load. You will get a really cool 3D curve and likely win some scholarship money (and might even learn something) in the process.

Re: Treads, Tracks, Tank system Talk/Help
 

Has there been a game yet that REQUIRED teams to climb obstacles? Seems a lot of the successful teams from 1999 and 2004 found clever ways to avoid climbing things.

Re: Treads, Tracks, Tank system Talk/Help
 

There have been games with obstacles that needed to be climbed. But I understand what your saying.

But treads, WHEN DONE RIGHT, are a great option for maneuvering up and over obstacles such as steps, ramps, etc...

There is a reason why tanks use treads.

Re: Treads, Tracks, Tank system Talk/Help
 

Now to get back on subject. His question wasn't "Should I do treads?", but "How can I best do treads?".

1. I can would agree with some other posts in this thread that 2-speed is a great way to go as far as treads go. A lower gear for turning, pushing, and getting over obstacles and a higher gear for everything else. I would recommend something like a 15:1 for low gear and a 10:1 high gear but this is really something you have to play around with. I don't know what your target range is. The low gear is the most important to figure out, as the high gear is really just what you want your speed to sit at. You have to make sure with your low gear to not get screwy with the amperage.

2. The walking effect as others have mentioned is from the treads overcoming the enormous amounts of friction. A great way around this is decreasing your floor contact. Look at the picture of 522 i posted earlier.

3. From experience, I know you do want to go with some sort of tensioning system. Look at the way many teams tension chain. Many of the techniques can be replicated with belting. You want to make sure to get a good wrap on your drive pulley(s). So keep that in mind as well.

The one thing you need to realize is that More Tension = More Current Draw. Less Tension = More Slippage. You need to find a good spot.

As far as general experience goes, when I was on 269, we tried treads in 2006. We made the mistake of using friction belts instead of timing belts. Needless to say, we failed miserably and stripped out the whole drive at our second regional and replaced it with 2 wheels.

Re: Treads, Tracks, Tank system Talk/Help
 

I see tank treads as having two advantages. One is in the real world where you have heavy vehicles on very soft and irregular ground. They do help reduce the ground pressure, as is beneficial for tanks and agricultural tractors. The other is in climbing over irregularly shaped objects, as there is a piece of tread that can catch whatever traction surface is available and not leave you "high-centered". The downside comes on a somewhat regular and relatively high traction playing surface where you have to contend with turning and keeping the tread on.

My personal experience only extends to 4 wheel drive using fairly large, pneumatic tires (Skyway). Those things had more than enough traction to make turning difficult, despite a very short wheelbase. In one regional competition shoving match, we and the opponent both flipped over backward as a result of a standoff pushing match. Neither robot moved more than a couple of inches one way or the other.

In terms of "best doing treads", what are peoples opinions on the number of drive and bogey wheels, and methods of tensioning?

Re: Treads, Tracks, Tank system Talk/Help
 

Before you start, really do consider tires if this is for a FIRST robot. We used tracks in '04 and '06, and found tires to be far superior ('08). 6WD or a 6x4 have proven to be great drive trains.

For us, a sliding/clamping tensioner proved very effective. Our favorite and lightest tensioning scheme was on our '06 robot. The last wheel mount point was on a seperate piece of aluminum which has a slot milled out of both of it's sides which slid in and out of a groove milled into the main part of the frame rail. So, to tension, you just took something like a screwdriver and pried the tensioner away from the frame rail hard as you could, then tightened two bolts that clamped down the tensioner (the two sides of the tuning-fork-like cutout in the end of the man frame rail). As a note, the only problem with our '06 robot's track system was in the design of it's bearings: the design of the bearing mounts had too loose of tolerances, which allowed the end sprockets to deflect slightly, allowing the track to work itself off if hit from the correct angle while doing a turn. As a redesign, simply taking more time to make each bearing pack would have eliminated this problem.

We used BrecoFlex both in '06 and '04 on custom FDM sprockets.

-q

p.s. If anyone wants a picture of the tensioner clamp system, just let me know and I'll see if I can dig up one or two to post.

Re: Treads, Tracks, Tank system Talk/Help
 

"...really do consider tires..."

I agree. If we were competing on a course of loose gravel or shale, I'd seriously consider tank treads. Otherwise, I think it is overkill. Do not confuse cool-looking with effective. As they say, "Run what you brung". The results will tell...

Re: Treads, Tracks, Tank system Talk/Help
 

In the context of FIRST, the only real advantage treads has is in climbing obstacles/uneven terrain.

I also believe that in every game so far, there were much simple ways to traverse the obstacles than treads. It'd take some really rough/odd obstacles to get me to advise my team to use treads.

Re: Treads, Tracks, Tank system Talk/Help
 

Yes, the reason is that they are better at spreading the weight of an 80 ton battle tank when crossing mud.

I won't advise you how to do tank treads because I don't know how, but I will advise you to look to the military and their move away from treads. (run a search on Stryker) Tank treads are great for uneven and shifting terrains but for speed and maneuverability they are not the most effective.

Now, would it be cool to do a tank tread system that could climb a 70 degree incline as a demo? Oh you bet it would be. My best suggestion would be to look at the military tanks and how they work. An interesting thing to do might be to have a way of letting your treads lose friction as they are moving sideways (similar to omni wheels) Might be interesting to make work, dont know how useful it would be though.

Just my (programmer's) $.02

Re: Treads, Tracks, Tank system Talk/Help
 

I started this thread to help myself and other to improve and create ideas about track systems. Though it seems most here are rather happy to bury them in the ground and call it a night. I admit that a track system may not be the best drive system or easiest to build but that doesn't mean that they wouldn't be as effective to a game as any other drive system. It truly depends on how you build you machines and how you operate it.

To step back to the main part of my project folder which i didn't want to do . Here is the true purpose:
To create a universal framework that can be use for the most of the FIRST drive trains and to be suitable to the challenge.

So in my work I'm at the final part of this which is adapting it to a tank type since the wheeled versions are completed. Though since for track systems i only know a few minor things about I figured I might ask around to team who have tried them to get a better idea. I really don't want to talk about my projects since i filled in the gaps to this point and wanted to keep the thread focused on what i didn't know and what could be done for track systems. The funny thing is i didn't expect it to get unfocused and try to push me away from a track system.

Re: Treads, Tracks, Tank system Talk/Help
 

Image from back in the day

I'm not sure if I can be much help to the cause but our team ran tank track back in the day, though now we are know by those who visit our pit for drum wheels.

Recently two of us attempted to resurrect this robot and learned a little about how the treads worked. It was tensioned with a worm gear, and before the old gear boxes gave way seemed to maneuver fairly well with the tension on the looser side of tight. It wreaked havoc on the breakers though you could year them popping clear across the shop when the tension was too great and it tried to draw more current.

Re: Treads, Tracks, Tank system Talk/Help
 

You've gotten a pretty consistent answer: the best way to do tank treads is not to do them. :) It seems that most teams who have tried tracks don't do them anymore. There's probably a good reason for that.

Re: Treads, Tracks, Tank system Talk/Help
 

Do people fail to see i will not take that answer, i will not quit if i fail the first time, I'll try again until i get it right. I feel that since i put help into the title i would get only help and some talk about track systems. So in my mind i feel that if you going to post anything about going to wheels or saying flat out that tracks should not be used i will close this tread and only communicate to those that have given interesting ideas and help. So help me if enough people do this I'll close the tread and not support the post count that it has generated for you just to try to kill a plausible idea.
People seem to think i know nothing about wheels here or any other type of drive systems, That i may lack the understanding of advantages and disadvantages, that i may not know strategies or something...............................I'm sorry just please for the love of something just help me with my questions and not put some tiny little post saying not to do this. Personally i never said it was for competition, i never said it was for cool factor, i didn't say it was for a lot of thing but people here seem to assume. I don't know what to do anymore i think i have enough to live by that i don't need some people here being bias and persecuting a idea. Man i feel like i might as well be in the past trying to challenge the church or something for wheels.