[FTC]: [FTC]: RobotC Template Problem (causing an FMS issue) and Potential Servo Prob

[PackersFan]

For some reason, the new joystick driver has some issues. We followed the online tutorial and installed the new one, but the new joystick driver causes connection issues with our NXT. We cannot connect via bluetooth with it at all, and downloading with a USB can be buggy as well. I know the problem is joystick driver related because we used the exact same code (just out of the template) but we used the old joystick driver (which we renamed) and the robot preformed just fine. This means that we cannot run the FMS at all, and we cannot test the new templates as we can only run the FMS when connected via bluetooth.

And then as another issue, we have a robot that struggles to pick up more then 8 pucks in a plexiglass basket using 6 servos. Could there be any issue that might be causing a problem, or is this just the limited power of these servos?

Thank you so much for your help.

[jbbjjbt]

Originally Posted by PackersFan

For some reason, the new joystick driver has some issues. We followed the online tutorial and installed the new one, but the new joystick driver causes connection issues with our NXT. We cannot connect via bluetooth with it at all, and downloading with a USB can be buggy as well. I know the problem is joystick driver related because we used the exact same code (just out of the template) but we used the old joystick driver (which we renamed) and the robot preformed just fine. This means that we cannot run the FMS at all, and we cannot test the new templates as we can only run the FMS when connected via bluetooth.

And then as another issue, we have a robot that struggles to pick up more then 8 pucks in a plexiglass basket using 6 servos. Could there be any issue that might be causing a problem, or is this just the limited power of these servos?

Thank you so much for your help.

I can't help with the RobotC issue, but as far as the servos, we have a bucket with 4 servos to move 8-10 pucks into the 12" high goal. It is very difficult to get 4 servos in sync with each other so 6 would be even harder. When they aren't in sync, they fight each other and won't due the job you're trying to do. We also find the servos dont last very long and have to be replaced often. So check to make sure your servos still work. Another issue is the moment arm for your basket, if you are trying to get the pucks into the high goal, servos probably don't have enough umph unless you use counterweights or some way to get leverage.

[PackersFan]

Thanks! Yeah, we're only going for the circle goal. How would we go about syncing the servos? We have checked to make sure that they all work, but I will keep that in mind.

[jbbjjbt]

Originally Posted by PackersFan

Thanks! Yeah, we're only going for the circle goal. How would we go about syncing the servos? We have checked to make sure that they all work, but I will keep that in mind.

What we do is
1) Move our bucket to the first position and make a mark on each of the servo holders
2) Move our bucket to the second position and make another mark of a different color on each of the servo holders
3) Take off the bucket and adjust the servos (Numbers in move servo command) until each one goes to the marks when told
4) Put the bucket back on and test. You may have to turn on the robot and run the servos to one position and then attach your bucket to get it lined up. The servos should be nearly silent if the numbers are correct. If there is alot of vibration or they move really jerky try again.

[PackersFan]

Our servos are fastened to each other. They don't twitch, but they do vibrate and make noise. Should we try to sync them differently or would this still work?

[ttldomination]

Are your servos facing each other? Like []- -[]. If they are, you must know that the values are flipped. and the two servos are resisting each other. For one servo, 255 is up, and for the other, 255 is down.

Is this how you have them?

[PackersFan]

The servos are facing each other and they are inverted.

[ttldomination]

Hm. THen it could simply be that they are carrying too much weight. We had this issue with our bot, where the servos would hum and twitch, but the arms were just too heavy.

[EricVanWyk]

DISCLAIMER: There is an 85% chance that I am completely wrong.

Servos are nominally position controlled, but you want them to add their force together. To me, that indicates that you want to make them force controlled.

If you add a bit of series elasticity (a rotary spring), you might be able to add enough slop so that they aren't fighting each other so stiffly.

I'd prefer if a MechE chimed in here. It just seems analagous to a few things I do as a SparkE. For example, lets say that I need to use several linear regulators in parallel. These are nominally ideal voltage outputs - very stiff. However, they will each have a slightly different idea of what 5V is, so one of them will take over. One solution is to add small resistors afterwards to ensure load balancing. This takes the very stiff controls and give them a more forgiving slope.

[PackersFan]

Originally Posted by jbbjjbt

What we do is
1) Move our bucket to the first position and make a mark on each of the servo holders
2) Move our bucket to the second position and make another mark of a different color on each of the servo holders
3) Take off the bucket and adjust the servos (Numbers in move servo command) until each one goes to the marks when told
4) Put the bucket back on and test. You may have to turn on the robot and run the servos to one position and then attach your bucket to get it lined up. The servos should be nearly silent if the numbers are correct. If there is alot of vibration or they move really jerky try again.

Could you go into more detail about that method? What I'm getting from the first and second positions is the starting point and the ending point, is that right? Also, where do the marks go and what purpose do they have?

[gdo]

For our servos we are doing 2:1 gearing, we got the spacing to work out just right. Here's a picture of it. There are 1 pair of servos on each side of the basket. With this method, we managed to get the servos at exactly the same position, for this side 255, and then drop the arm ontop, the servos have little problem with keeping at the same position, and so far we have had no problem w/ torque either.



Sorry for the quality, my camera is MIA so I had to use my webcam on my laptop..

[jbbjjbt]

Originally Posted by PackersFan

Could you go into more detail about that method? What I'm getting from the first and second positions is the starting point and the ending point, is that right? Also, where do the marks go and what purpose do they have?

You are correct. The marks are just on the sides of the servo holders so you know where the servos go to with the bucket off.

We find the even with two servos oriented the same, the number for a position may be up to 20 or so different for the two different servos.

Also you don't want to drive the servos clear to the limits (1 or 255) if the arm is mechanically stopped sooner. We were driving our servos to 255 but the bucket hit the goal at 220 and this was breaking the servos.