Team #405

Looks awesome! It's built like a racecar (and I like the strategic batt. placement)

I would highly suggest switching the servos to a globe motor(s) with a differential (what we're doing).

Also, why did you decide not to do an Ackermann front steering?

[Wayne Doenges]

I would also HIGHLY recommend the Globe motor. The HS-422 Hitec servoes only have a torque of 42 OZ/in

[bobzdar]

Originally Posted by Jaybee1405

Looks awesome! It's built like a racecar (and I like the strategic batt. placement)

I would highly suggest switching the servos to a globe motor(s) with a differential (what we're doing).

Also, why did you decide not to do an Ackermann front steering?

I think the way the servos are actually doing the steering there's not a lot of pressure on them. As I said, we have an alternate steering mechanism in the works just in case we have a problem.

In regards to why we didn't do Ackermann steering...the alternate steering method incorporates it, though from what I can gather it won't make a big difference at higher speeds and we are going to run a little toe out so the car doesn't dart around which should make the inside wheel turn tighter. If we want to incorporate Ackermann steering in the current design, all we have to do is move the tie rod pivot points in a little, but it may stress the servos a little more as then they'd be fighting each other a little bit at max lock. We'll see what the students come up with. I'm heading over to the school now, I'll try to get some videos.

[boonski]

What are the dimensions for your robot? Because it looks really small in the pics.

[jimbot]

Don't use sevos period. Our team 2083 built a car robot last year and used servos. They held up fine in regionals, but at worlds they started to fail like crazy. Every match one would go and we would have to replace it. DON'T USE SERVOS!!!

[bobzdar]

Originally Posted by boonski

What are the dimensions for your robot? Because it looks really small in the pics.

It's about 26" wide and 32" long, but should be right around 36" long once the bumper mounts are put on.

We removed the servos and went with the globe motor but won't have it running until Monday or Tuesday as it'll need some software work. We found that the servos didn't provide enough turning radius and when we increased the pivot, they'd start to lose power so we figured we wouldn't risk it and made some changes. Before removing them, we did do some speed testing and went about 35' in 3 secs from a dead stop. We may gear a little higher to prevent wheel spin as it seems to have a little too much torque right now.

[Fastnate]

Wow, that looks really nice.
Good luck!

[bobzdar]

Thanks for all the comments, we switched to a globe motor on the front with a pot and now have around 55 degrees of steering lock (on the inside wheel, it's ackerman so around 40 deg on the outside) and no issues with power. The wheels won't be exposed, we're going to run bumpers all the way around and nothing is going to be attached to the front or rear end so that they aren't stressed in an accident and are easy to remove for repairs if need be. The robot is pretty much finished now (except for the bumpers), I have a couple of pics of it, see below:



Total weight as shown is 84lbs. We figure we might get it up to 90lbs with bumper mounting brackets and the cage around the front and rear wheels, so still 30lbs under weight.

[corcarter]

you have some messy electrical work >.<

[iwashere1990]

Whats the turning radius of those wheels? Seems short imo...Then again, it looks very fast. Good luck.

[JesseK]

For your stationary turning issues, I'd like to point you to this thread:
http://www.chiefdelphi.com/forums/sh...hlight=current

Note the posts by Dave Lavery on the total current available to the servos. It's only 1 amp . When you're stationary, you have evidence that your servos have trouble manipulating the steering. I'd be weary about this, as the mechanical stresses combined with current pull could be the cause of servos burning out. I'd have plenty of spares if I were you.

Also, I'd recommend putting some sort of support going from the main drive base to right next to the front wheels, or enclose the whole front. At the moment, a high speed off-centered frontal crash will knock your steering out of alignment, regardless of where you mount a front bumper to the current design.

Otherwise, this looks like a fantastic drive train!