Image Discuss: 121 Teaser 1
 

Hrmm.. Question...

how do you guys deal with the fact that the Chippy is alot more powerfull than the Bosch motors, and.. im im not mistaken runs slightly faster than the Bosch?

~Pyro

Our driver is trained to hold the joysticks at different angles. j/k what we really do is gear ratios.....

The drill motors are actually the ones that are more powerful, about %50 and they also spin at a speed almost 4 times greater than the Chips. I understand now to match the speeds but how in fact do you adjust for the difference in power? Its like driving one side with 2 Chips and the other with 3.

that was last year. the drill motors are a lot more powerful last year

hmmm, you obviously never saw the drive train on Team 121's bot last year - it had the same setup, and worked very well. I also know that it was quite fast enough to give us (team 571) quite a headace when we tried to push them out of the way.

the left and right side , i believe, are run at different gear ratios in order to achieve the same speed. (true, one side is probably a little more powerful than the other, but i don't think that that affected anything much.

if you do it right like we have everything is same speed and power throughout.

Is that an illegal battery in there though?

I don't see how it would be. The battery can be in any orientation

But it doesn't look like the one in the kit!!!

We have multiple batteries that are not Exide, and use them for testing. To tell you the truth, I don't think there is a rule that you are required to have an Exide Battery.

wow...im really interested in your grearing system, i can't come up with numbers to make those run at the same speed and still have the same tourque....u can bet i'll be visiting your pit alot....good luck

well, the only way that i can think of for the power matching is in code. By limiting how much power goes to a particular motor...

It doesn't make sense to have 2 totally different types of motors to put out the exact same thing mechanically w/ or w/o gear ratios....

ok you wanna know what really powers our wheels. WE put these guys in little metal boxes and let them turn the wheels. THis is an artist rendition of what we do. We also feed the gerbils the same food. so power is equal. To make the bot turn one way, we use brakes on the gerbil wheel to stop power.

Page 8- The Robot
thats what the rules say

Just don't put them in the microwave and cook them. We talked about this in chemistry today, and the blow up.

That reminds me of a story about one of our alumnists.... you know who you are! ;)

Are you sure about this? I was under the impression the drills this year are much more powerful than those from previous years. Can someone confirm this?

In theory having more torque on one side of your drive would hinder straight line acceleration since one side would be accelerating faster than the other provided there wasn't any wheel spin. In other words the robot would have a tendency to turn in one direction when accelerating. I suppose this could be corrected w/ programming but you would be putting yourself at a disadvantage since you would be giving up the power of your stronger motors to match the power of the weaker set.

I thought that Woodie spacifically stated that gerbil power was not allowed this year....

Great Bot guys

So the robot would want to turn in an arc. That would be terrible in a game like this, huh?

Well if you want to use dead reckoning for the autonomous period its really really bad. It basically limits any ability of yours to determine where it is going to be.

I highly doubt the arc you would get is what's desired during autonomous, and even if it was when you think about all the variables involved the drive would still be at a disadvantage. Never the less it is an interesting way of taking the arc. Theoretically you could tune the speed of your robot to take the correct path, you wouldn't be the fastest but the system would require virtually no programming skill whatsoever.

Our drivetrain is similar to last year, and while I can't say it goes in a perfect straight line, I can say it doesn't go into an arc. Truly you only notice it if the robot is going down the whole field, you notice that pitched a little to the left. Our auto programs are also good, and they actually use right angles to find its desired path. It's a really good drivetrain system, and served us well last year.

I just want to make it clear I'm not trying to put down the drive system it looks to be one of the better systems I've seen. It actually isn't all that far from our own system this year. The differneces in acceleration and power I mentioned are so minimal chances are you won't notice it on the field and it wont have any bearing on the overall performance of the bot.:D

How well are you guys at turning? We used the same wheels and we have four wheel drive, using a drill and cim on each side, but when we turn it doesn't want, well it will, it just jumps a lot and beats up our bot. I was wondering if you might have had any trouble andfigured out something or if it is just us. We would appreciate any help we can get. Anybody?

As driver of our robot, the drive train works great, with 6 wheels instead of just 4 like last year, it grips the carpet a little more, causing it to bounce a little bit, but it all depends on how it's driven. If I take it easy when turning it's fine. I don't think i'm going to have to do a lot of quick manuvering, so we should be all set. Also the carpet we tested on was hardly secured and bunched up, it should be better at competitions. All i can say is that you should take it easy when your driving.

Matching up torque-speed curves can be tricky, but it's beneficial if you get it right.


The new drill motors put out 193 oz-in of torqe at 1,100 RPM at their maximum efficiency (65% drawing 21A).
The CIM motors put out about 64 oz-in of torque at ~4400 RPM at their max efficiency (76% drawing 23A).


When adding a typical 10% inefficiency for gearing the CIM motor, you can see that the motors are rather close.

Six wheel drive
 

Do you do anything special to make your robot turn? Normally all those wheels on the ground would make turning difficult. We found that our Bosch got really hot (while the chip's were relatively cool) we solved that problem by cutting the power to the bosch in half, now both the bosch and the chip's get equally hot under strenuous circumstances.

We have a six wheel design (have for every year), and offset the center wheels by 1/4" so the robot is actually balancing on the center wheels: makes for easy, friction free turning. GOtta use the Gyro for stabilization, however, because it turns TOO easy!

Photos at http://www.barello.net/FIRST/Images

we have a strong 4 wheel drive system that would jump during turns on the carpet. We fixed this easily by adding two caster wheels on the back that are threaded on 3/4" bore 2" stroke pneumatic actuators. when we are on the carpet they are down for easy turning and when we are on the ramp they are up for traction and pushing power. All at the click of a button.

our robot has 6 wheel drive on drill 2 motors, we had to smooth the wheels though. There was a ridge in the center that prevent sideways movement of the wheels on carpet. As you might expect the drill motors kept on overheating. We smoothed this ridge of, so we now only have grooves that provide traction in a forward or reverse direction. We CAN turn very well and have a lot of control on the HDPE. So far we have been able to push robots on the mesh while we are on HDPE. Check out our bot by doing a search for " image 930 " on chief delphi. Look at the thread, there is two pics.