SES Arm - troubleshooting

SES Arm with wrist rotate upgrade.

I got the arm a while ago and recently started setting it up. I had a few problems getting it to work, but eventually realized the 9vdc battery I was using was bad. So, now VL does not equal VS1 and I have a brand new 9vdc bat. hooked up to VL.

Baud = 115.2k
TX=RX

I can’t tell if I burned something out, but the problem at the moment is that the base servo rotates all the way to the CCW side when I apply the “ALL=1.5mS” in SSC-32 V1.05 or Lynxterm V1.10 “All=1500”. When I first got it working this morning, the servo centered… now it doesn’t. I assume I changed something, but haven’t got a clue what.

Also, when I got Lynxterm working, I could play with channel 0 and rotate the Base servo, but it didn’t appear to rotate to anything less than 1600 and rotated until maxed out at 2250. A strange quirk is that the servo seems to jump past about 15-20° of rotation around 1600-1700. What I mean by that is I will slowly increment the pulse and the servo will slowly move until it suddenly moves several degrees and then slows down again and resumes making small increments as I increment the signal.

With no Pulse
9vdc battery drop ~ 9.4V
VS1 ~6.93V
VS1=VL ~2.41V (unhooked)
VS2 ~6.93V
Pin 4 Red>Black ~6.93V
Pin 4 Yellow>Black ~0 (no pulse)
I have a green light on my board

With Lynxterm “All=1500”
9vdc battery drop ~ 9.4V
VS1 ~6.90V
VS1=VL ~2.48V (unhooked)
VS2 ~6.90V
Pin 4 Red>Black ~6.90V
Pin 4 Yellow>Black ~0.40 (All=1500)
Green light is off

During these measurements only the Base and Shoulder servos were plugged in.

I haven’t gotten any further than the “Test” in the main SSC-32 screen because I was trying to line everything up when I hit this snag. I’m not very familiar with the software, but I’m quite proficient with computers in general.

All of the voltages you measured look correct. Remove the servo from the base and try it again. It’s possible that the mechanics in the base are causing the servo to bind. You can also loosen the screw in the center of the base rotation plate to see if the problem goes away.

ok. While I was testing I had the center screw loose. I’m at home at the moment and the bot is at school, so I’ll get back to testing it tomorrow or thursday.

Better just remove the servo from the base to rule out any mechanical problems. Let us know the results.

with the base servo completely removed, it still turns all the way to one side with a center pulse.

testing channel 0 with a different servo and the same pulse causes the servo to go to center as expected.

does this mean the base servo (HS-422) is buggard, or can I attempt to fix it somehow?

Buggard, buggard, buggard…

It means one half of the h-bridge is shot.

that sucks…

well, I got a HS-475 that is used for the gripper… would that work in the base for lifting items that won’t be more the 20 grams?

We’re replacing the gripper with a bellows vacuum end effector anyways, so the servo will be extra.

The 475 is a great servo for the base.

awesome, thanks for all the help