Hello all! Newbie question. Searched for quite awhile, but couldn’t seem to find a topic already about this (feel free to correct me if I’m wrong).
When powering on your servos/servo controller, is there any way to stop the “servo jerk” at the beginning? That is, when the servo goes to it’s center position at full speed. I’m designing a custom robotic arm, and this is somewhat of an issue when turning it on. Any info would be of great help. Thanks!
Using:
BS2
Parallax servo controller
Various standard servos
The problem is the servo controller you are using. The SSC-32 allows you to set the initial startup positions of the servos. Rather than starting the pulses at 1500 (centered) you can start the robot in a “home” position. The SSC-32 has many other cool features, but this is the one that will fix your jumping servos at startup problem.
I have the older SSC-32 (non-usb) board - is there a way to set the “home positions” using and Arduino board (UNO)? I’m a mac user and it’s a bit inconvenient to hunt down an old serial cable and also to figure out how to get the software to run on my mac using a virutal machine
No luck… the issue is a bit different, I think. I have the SSC-32 connected to a relay so that I only deliver power to the board when I need to control the servos connected to it. The moment the relay is flipped and the SSC-32 receives power, the servos all twich/jerk. The jerking is consistently in one direction and appears to be consistently in the same “amount”… it’s about half a second and then they stop moving and, presumably await commands.
I can still move the servos manually, so they are not receiving any sort of hold position, but every time I power up the board, they jerk.
Does the twitching stop after a second or two, or do they always twitch until they receive a command? If you can provide some photos or even a video it would be appreciated. Specs for the relay and anything else you are using will help avoid back and forth.
I can create a video if need be, but it’s only for about a half-second after the board first receives power… then its fine and operates normally thereafter. It’s only when it first receives power.
Ideally, I would want to have the board (and connected servos) powered off until I need them - power conservation, of course.
It sometimes happens that the servos might spasm slightly when the SSC-32U’s processor boots up, though they should not try to move and immediately go limp.
So there’s no way to overcome this, is that correct?
I guess my solution would then be to always have the board powered-up, but have the power for the servos controlled via the relays so that they’re not drawing any current until needed; would you agree?
Very nice swerve drive robot by the way.
Servos react to any pulse which they receive - even a small pulse which the microcontroller may be sending out upon startup.
The way around this would likely be to connect the servo power after the SSC-32U has already been powered.
Thanks Coleman - he’s a never-ending work in progress …getting there though!
Yeah, that makes sense; I guess I’ll have to use-up two relays to do it, but the site says that the board has a Current requirements: 31mA; that’s quite small; is that all it uses when at idle (i.e. just the logic circuitry)?
Well… tried your idea, but it’s a fail… even with the servo board having been powered up, separately from the servos, the servos jerk when they get power initially. It’s the same jerk you saw in the video I posted… so it’s when the servos (HS-785HB Winch Servos) get power that they jerk on power-up… any other thoughts?
Response from Hitec: “It is not uncommon to see a slight twitch when powered up, especially if there is a slight load on the servo. It should not be a large deflection however.”
Yeah, I’ve been hunting on Google and found that it’s a thing, apparently. It’s the signal line to the servo - it’s not the power, however. There were some suggestions of putting a 10k resistor on the signal line to the servo, but I tried that to no avail… same jerk even with the resistor in-place.
