Anyone have BS2 and Digital Servo Experience?

Robot Jay

I bought some digital servos at a good price and now I want to use my BS2 to control them.· When I use a pulsout command with these digitals, I actually don't have to worry about repeating pulsout commands.· One command sets the servo to a certain position.· (i.e. "PULSOUT 12, 250" sets the servo to its·clockwise limit.· "PULSOUT 12, 750" centers the servo.)· ·It seems though, that not every pulsout command I send is being received.· Sometimes the servo responds, sometimes not.· If i resend the command a few times, the servo eventually responds.· I am just curious how many users out there have experience with the BS2 and Digital servos and if they've encountered similar problems.

iamscottym

Digital servos use proprietary signals, and as far as I've seen no one has released their signal info yet. You can damage your servo sending it an analog signal(I think, I know the reverse is true), but if you're just outputting an analog signal, why use a more expensive digital servo anyway?

Chris Savage

All the information we have shows that digital servos are fully compatible with standard servos.· I don't know whether or not they require refreshing, but one thing I would try is making certain the I/O line is LOW by default so the pulses are read correctly.· Try putting a LOW 0 or whatever line you're using in your code before sending pulses.

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Chris Savage
Parallax Tech Support
csavage@parallax.com

Paul Baker

My understanding is in line with Chris' comments. Digital servos use the same interface as analog, however thier internal method of controlling the servo is different. Analog servos perform thier operations from the supplied signal (changing direction, speed, feedback etc), digital servos store the data, meaning it can continue operating the servo in the "dead period" of the signal. This allows for more aggressive control if desired, and provides a means for programing the servo's behaviour (top speed, travel, dead-band, etc). You should not be experiencing the problems you are. If Chris' suggestion doesn't work, then perhaps the servos were cheap for a reason (most digital servos cost $50 or more).

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1+1=10

Robot Jay

Ok, so I got tired of the servos not responding properly, and I·got a Parallax Servo Controller.· I now have only a few issues with my servos, but I don't think that the Stamp/PSC combo is the problem anymore.· Just for future reference, the servos I am using are TowerPro MG995 "Digi" Hi-Speed Servos (NOT Digital, as one might believe.)· These servos cost me·$17 each.· 180 oz-in (13 kg-cm) of torque.· As far as I know, regular standard servos aren't even this cheap for this much torque.· Although these aren't Digital, I do believe that they are·NOT standard.· For instance, there is no centering screw.· If I send them a pulsewidth, they go to a certain position and hold.· If I try to move them with my hand while power is being applied to them, they continually resist the force I apply without having to send code to the servo.· I don't think they are truly digital though because I have noticed that the servos "jitter" randomly.· For my project, this is not too big a problem, but others might find it a nuissance.· The jitters are small, and for the price I paid, I can deal with it.·

I am not sure what the difference between the way the PSC sends pulsewidths and the way the Stamp itself sends commands is, but I no longer have any issues with servos being only partially responsive.

Chris Savage

Standard servos do not spin contiuously, nor do they have a center set screw.· The have a range of around 180 degrees and go to the center of that renge (roughly) when sent a center (1.5 ms) pulse value.

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Chris Savage
Parallax Tech Support
csavage@parallax.com