Re: Has 6 wheeled designs surpased tank treads
 

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.

Re: Has 6 wheeled designs surpased tank treads
 

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

Re: Has 6 wheeled designs surpased tank treads
 

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.

Re: Has 6 wheeled designs surpased tank treads
 

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.

Re: Has 6 wheeled designs surpased tank treads
 

look at the evolution of the competition, apparently tank treads were popular when we had ramp style competition. where as 6 wheeled designs have come into play mostly with the new start style.

Re: Has 6 wheeled designs surpased tank treads
 

Tank treads can be complicated, depending on what your recourses are, for instance a simple bot as shown above is easily made, but wouldn't stand up against last years competition. one of the teams at our regional last year used treads, their goal was to climb the steps, but weren't able to and ended up just pushing around balls. I personally favor treads for their easy drivability. And Ken, i could easily make the mounting brackets if you drew them for me, being i have a maxnc cnc milling machine in my basement, which everyone on my team seems to forget. :yikes:

Re: Has 6 wheeled designs surpased tank treads
 

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.

Re: Has 6 wheeled designs surpased tank treads
 

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

Re: Has 6 wheeled designs surpased tank treads
 

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

Re: Has 6 wheeled designs surpased tank treads
 

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"

Re: Has 6 wheeled designs surpased tank treads
 

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.

Re: Has 6 wheeled designs surpased tank treads
 

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.

Re: Has 6 wheeled designs surpased tank treads
 

All you tank tread lovers, educate me on the following things:


1. Show me the math that shows tank treads have better pushing force (traction) than a wheeled design.

2. While doing number 1, assume whatever tread material you use for the tank tread can be wrapped around a wheel.

3. Leaving the obstacles out of the equation (stairs, ramps, etc.), why do certain vehicles have tank tread designs (tanks, excavators, snow mobiles, etc.)?

4. Again, leaving obstacles out of the equation; what advantages are there for FIRST robots to use treads? If you say pushing force, or traction; then prove it with math/physics.

I look forward to the range of answers.

Re: Has 6 wheeled designs surpased tank treads
 

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?

Re: Has 6 wheeled designs surpased tank treads
 

Well, this depends on the material of the wheel mainly. If you are using solid rubber wheels, then you only need to lower them a very very small distance, just to take pressure off the outer wheels. If you are using pneumatic tires, the amount that you need to lower them is greater because they will squish down under the weight of the robot. This is just a general rule, the actually distance depends greatly on the individual robot with its many factors, such as weight distribution about the robot, where the idler is located on the robot, etc.

There is also a sort of balance between current and controllability. If you lower the middle wheel a lot, then you will maximize current saving, but you may encounter problems such as your robot drifting from one side to another, or teetering back and forth (which can be annoying). But if you don't lower them enough and all 6 wheel are touching the ground but pressure is off a set of them, you will eat up current trying to turn but you will have more controllability. So, I guess its best to experiment with your design to come up with what your team is comfortable with.