Re: Team 1535 Knights of Alloy Nearly complete robot!
 

Realistically, you can beat many of the problems with casters with sensors and programming. Throwing a gyro on there, with a PID loop to control rotational rate should keep your drivers happy, and you bot from freaking out when hit. Our team is going with rear omni wheels, and i've come up with a system that should eliminate many of potential issues. Also, with unmovable defense pretty much nullified this year, bot's spinning each other out should occur much less.

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

Very impressive. I've always been a big fan of two wheel center drive. It looks like you guys have it down.

About the casters- In many instences, casters are not the greatest idea. Normally you see them on rookie robots with two up front and two driven wheels in the rear (the shopping cart method). This is a inherently unstable design and a real bear to drive. However, what this team is doing is very different.

If you look closely you'll notice that there are 4 casters, one at each corner of the bot. In the 'middle', are two large wheels, presumably powered. These wheels will be slightly lower then the casters. The robot will be balanced such that the majority of the weight will center over these wheels. In other words, if you were to put your hand on the robot, it should slightly seesaw back and forth on the center wheels.

This is an excellent drive method for this years game. Unlike a 4 wheel drive train there is no scrubbing when turning. The robot can spin in place all day with no more strain or current draw then if it were going straight ahead. This means that the robot is very quick and easy to turn and has real neutral handling. Point of fact, it's just like a Segway.

So how do the casters fit in? Well, unlike a Segway, FIRST robots aren't quite clever enough to dynamically balance (somebody prove me wrong, please!). The casters just keep the robot frame off the ground. Other teams have used plastic skids or idlers in place of casters, but it's really a matter of preference. Because there is so little weight on them and the drive train so efficient when turning casters won't present any hardship. When turning the casters will either orient correctly or just scrub, but with out much weight on them it won't be noticeable.

I think this will be the year of the center drive.

-Andy A.

Other center wheel drive robots:

Team 885
Team 95 from 2002
Team 95 from 2005

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

I commend your team on a neat design!!!
You are much further along than many other teams...
If you can conquer the problems encountered with the use of standard casters.. more power to you... just give yourself a lot of swing room around them and you can do this.

I would suggest that you use something called a ball transfer rather than a caster. Take a look at something like McMaster Carr part 6460K47

They have a variety of these... and they are much more resilient to the rigors fo the game than standard swiveling caster.

Although, if you guys are making it work...
GREAT JOB...

I hope you really do well in the competition...

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

Thank you Andy, I was relieved to see your postivie post! I think our team is very happy with the caters. I don't know if I mentioned this before but they are spring loaded and yes the bot does seesaw just a tad.

About the ball transfer, I believe our team has looked into them before and had found out that they are not recommended for carpeted applications due to the fibers etc. that can get stuff stuck up inside the ball.

I want to thank you guys again for your input. We're really excited about this years robot!

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

I've tried to stay away from casters for a long time. They tend to "kick" to one direction or another during slow movement. Simple delrin or nylon pads in place of the casters could be better. (Think of it like moving a sofa with those nice plastic pads underneath.)
I love the arm though, not sure why I keep thinking everything has to be straight.

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

hey, my team, 2026 (i think) is new this year, and were having a similar design, as far as the forks go. i was just wondering how good your bot controls the ball if you have tested it out. thanks in advance

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

Looks good, but how do you plan to get the ball off of the overpass, or put the ball up at the last 15 seconds?

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

I'm back! To answer some more questions!

For starters: We have fixed our problem with the steering being touchy! WoOt! I am SO :) happy about that :D ! Our programmer fixed that!

Well Aren, here's the deal, we have used omni wheels for the past 3 years (including the years as 1596) so we decided to do something different. We decided that casters would be the best idea in spite of the fact that everyone seems to hate them!

We haven't had a chance to test it yet, because we found a problem with our arm. It did not have enough power:mad:! So we are doing some redesigning of it. But when we do I'll be happy to let you know, Corcarter.

If anyone else has questions I check this thread daily and answer the questions if I have the answers from my team!

Have a good one,
Boonski

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

WOOT!!

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

i cant see very well because of the pictures angle, but is there a motor on the end of your arm there? obviously to dump the ball on the overpass?

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

let me know if yall get that arm tested, either post here or private message me

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

looking pretty awesome.

I was just wondering, since you guys seem to be discussing drive-train issues, have you run into any problems as far as traction on your middle wheels? Team 1828 had initially tried a six-wheel system like yours, only to find that, if any amount of weight was concentrated to one end of the robot, the drive wheels in the middle spun uselessly.

Our first driving test almost looked like drifting. Glad to hear that yours seems to be working out fine.

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

hey guys(and girl/s), sorry to hear about your forks >.< man that sucks, better luck with whatever you all try next.

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

looks great guys, can't wait to see you guys at waterloo lol. I like how light it is, and if you guys dont figure something out for your arm, all you should need to do is a gear reduction up the "tower" you have, I noticed it looks like cim motor, belt driven right to the joint, try maybe a two stage reduction, it works wonders :D

See you guys in Waterloo!!

Re: Team 1535 Knights of Alloy Nearly complete robot!
 

Casters are for chairs ect not robots