caster....no

every how and then I have some imput that is worth while. How I think ill share that.

In this years game we experienced many robots with casters and and center drive. We were thrilled when we got to go against them, and disapoointed when we got paired with them. Why? Caster-bots can turn very quickly and efficiently. And if the game was all about this then it may not be a bad idea. But what you must know is that If I hit your robot anywhere but the front, I will spin you and then push you. You are also going to lose alot of ability to push other teams as well. The more wheels on the ground, the better, this will give you the most resistance to opposing motion.

One team that had a very sweet caster-design was team #9. This team rarely gets the credit they deserved but their robot performed perfectly. They set 4 wheels in the back of their robot (all powered) and had 2 casters in front for balance. They were able to turn effortlessly and were able to resist pushing and pulling quite well.

If you want mobility and power you can always use crab or omni drive (which are a little complicated) but otherwise you could use what we did. We had four wheels on the ground and had a caster attached to a globe motor that could deploy in under a second. As a result we could turn quickly and then pull the caster up for power. We were amazing at defending the stack, and I attribute it to this design, and awesome driving.

hope that helped

if you would like to use the ability of castors, and get the advantage of being able to have crazy manuverability... try omni-wheels. my team experienced with these last year. what it is if anyone hasnt seen these before, they are a small wheel and they have rollers made into the sides of the wheel, thus acting as a castor. the advantage of these tho, is you can power them, and not be screwed out for manuverability.

Re: thanks!
 

It is not uncommon for teams to try 4-wheel drive and not be able to turn. I've been working on a 4-wheel drive white paper that shows the calculations you need to make to ensure that your drivetrain will turn. I think it will be done this weekend, so I should be able to post it Monday morning.

"High centered" means that your robot is stuck on something (typically in the center of the robot). The term comes from 4x4 off-roading. Think of it this way: you're driving your Jeep through the woods and you attempt to drive over a large log that is across the path. You get halfway over the log, and your Jeep is now resting with its frame on the log, and your wheels can't get traction. This is because you have something high in the center of your vehicle - hence, your vehicle is "high-centered".

-Chris

I was too lazy to read all the threads so I hope I'm not repeating something but it is very possible to be successful with a center-wheel design. In 1996, team 73 used a center-wheel drive. The center wheels were just powered wheel-chair wheels. There were custom-made spherical casters on the four corners of the robot. The chief advantage of the center-wheel drive at that time was manuverability. This meant that it was possible to spin out of an engagement with another robot. I should also add, that 1996 was the year that 73 was national champions.

Matt

the main problem with a center drive 2 wheel bot is that when going up a ramp, the casters in front will raise your drive wheels off the ground, getting you stuck. 2 drive wheels in front and casters in the back arent that bad though (omni wheels in the rear are even better)

My general advice on drive trains:

Don't experiment! I mean, you have to start by experimenting, but once you find something that works (or see it on another robot, hint hint), go for it. Build it, test it, improve it and do it all over again. Team 71 prided theirselves on a special chain ratio with those old drill motors that they didn't change for several seasons until they got these new ones last year (even the walking 2002 model had a classic drive system in the rear). I'm not suggesting necesarily to use a two wheel chain system - but find something that you can build, maintain, and rebuild - that works - and stick with it as long as you can. Another example is Technokats - they have been using a tank tread system forever and even this year when their titanium treads were outlawed - they had a colorful red polymer of some sort in it's place.

My team (#95) had a lot of success with a design similar to this. Since casters really mess up steering, we used delrin "scrub wheels" instead. They would slip accross the carpet without trouble while still keeping the robot balanced. Since there were no ramps that year (2002) we didn't get our drive wheels lifted off the ground. We had some trouble getting pushed around, but our strategy was outrunning and outmanuvering, so we didn't need to push very much. The robot ended up being very fast and manuverable. Just don't use casters.

Re: Re: thanks!
 

Great, I can't wait to get a copy of the white paper to pass
it along to the NYC teams I work with.

Thanks.

Did your team go to the Long Island regional?? I remeber someone doing the same exact thing with their robot.

No; we were just at the Manchester (NH) and UTC (MA) regionals. It sounds like it worked for someone else, too.

That was Team 263, Sachem High School.

They've had 2-wheeled 'bots for three years running now, but only one (2002) could be considered a "center drive." The rest used teflon or delrin skids.

Teflon skids, but our 2002 bot also had them. We just had one on each corner and we balanced the weight around the robot so we just rested weight on the side opposite the dirrection we were driving, and then we didn't rest any weight on them when we had 2 goals.

Re: center-wheel drive
 

heres what my team used in 2002, it worked great, and we had high manuvarability


.......______
...../---O---\
.../----------\
..|-----------|
.()-----------()
..|-----------|
...\ --------- /
.....\ __O__ /


this is about what the bot looked like, 2 wheels on the sides, and two casters in the front and back, with the globes, it was incredible