Team 1246 Rookie Bot
 

How does it look? We're rookies and we only have one mentor, no machine shop, limited funds and a core team of 8 people and yet somehow we pulled this off. Only problem is, the globes are backdriving when we pick up the 2X ball!

Re: Team 1246 Rookie Bot
 

It may just be my computer but the picture won't load. :ahh: Is there a link or something you could put up?

Re: Team 1246 Rookie Bot
 

Amazing!!!

A very creative and functional robot!

I don't think I have ever seen bike tires before, but for this game it coudl be a great idea.

Great job guys, I am sure a team at the regional you are goign to can help you out with you globe motor problem.

P.S. Iain, the pic works for me. maybe its your computer.

Re: Team 1246 Rookie Bot
 

We're going to the Canadian Regional. I've already asked this before in a different thread but looking at where we placed our Globes on the bot, are there any suggestions how we can fix the backdriving problem? We can hang because we put stops after this pic so that the arms are all the way vertical without slamming back on the motors themselves, but we were having trouble getting the arm at 90 degrees with the ball where the moment is greatest. It just drops back down at that point. Also, this pic shows our temporary drive train with the fisher price. Our competitive drive train is a CIM + Bosch gearbox with 15ft/s optimal output. We were having trouble getting our gearbox in time because we sent it out to get machined so we tested our bot with the fisher prices just to get it mobile for practice and testing.

Re: Team 1246 Rookie Bot
 

Set speed controlers on break, gear down your arm with sprocket reductions.

Re: Team 1246 Rookie Bot
 

Robot looks good, can't wait to see it in action at the Canadian regionals

Re: Team 1246 Rookie Bot
 

Here is what we did (actually, we designed for this, its not really a fix on our bot, its a feature!)

Here is a fix: Add about a foot of garage door spring that will be pulling your arm up. You can stretch it as far as you like, but please be careful, seeing as one of thos springs can kill. I put a cable through the middle of ours and anchored it in two non-spring related places so that in the event of a catastrophic spring mount failure, the spring won't do any damage.

It is working great for us.

Re: Team 1246 Rookie Bot
 

Looks great, Fady. Can't wait to see it in action!

Re: Team 1246 Rookie Bot
 

You guys have done an excellent job with that robot. :) It is always difficult the first year and not to downplay the globe issue but if that is your only problem you've done even better being it's your rookie year. I wish your team the best of luck in the competitions.

Re: Team 1246 Rookie Bot
 

Looks great guys! Can't wait to see it in action. As for the globe motors, try switching the Victors into brake mode, changing the sprocket ratio, or you could even (though I would consider this a last resort) put a potentiometer on the arm so that the controller can sense what position it is in, and then write a program that will adjust the power to the motors to achieve a "target" position, measured by the potentiometer. Basically you would be turning the globe motor into a giant servo. What this will do, is as the motors begin backdriving, the potentiometer tells the program "They're getting away!!! :ahh: " then the program says "hey where do you think you're going :mad: " and gives them a shot of power to bring them back and hold them in the "target" position. The downside to this is that if they are holding a load of a long time, they are basically being stalled at a low voltage, and as a result, the brushes inside heat up, and the motor becomes unhappy :( .

Anyhoo, good luck! :)

Re: Team 1246 Rookie Bot
 

EDIT: Ignore this post. I gave an incorrect answer thinking they were using globes for hanging.

Re: Team 1246 Rookie Bot
 

We might end up using a potentiometer if all else fails. Can you give me info on where to get one or two (well, can we use ones at a local Radio Shack?) and how to wire them up, where to place them in the circuit, and how they work? Thanks.

Re: Team 1246 Rookie Bot
 

radio shack is good for pots, but I still say buy some springs (you can get smaller ones from a hardware store).

Re: Team 1246 Rookie Bot
 

So here's what we finally decided we're going to do to the arm the Thursday at the competition.

- Make it lighter (replace the 30 series extruded aluminum with 20 series)
- Use a larger sprocket on the drum (moves slower and more torque)
- Add a potentiometer to measure position of the arm
- Add a tensioner (sp?) for the belt
- Some programming modifications to improve control

We already have full position control of the opening and closing of the arm. We can stop the piston of the cylinder at any position. We should have similar control of the drum of the arm with the modifications.