Servotor32 Controller Board for use with Arduino?

Oz Stevens

The Servotor32 can handle 32 servos and attaches to an Arduino board like the other shields.  Is there a reason you wouldn't use this instead of a BASIC board that you would have to create and build to handle more than a few servos?

The reason I'm asking is that I am designing a life form animatronic that will need between 16 and 20 servos, be battery driven, and have several sensors that will cause reaction to near objects and touch sensation.

Arduino just seems to have more sensors and add-on boards than BASIC.  BUT, I am also looking for advice.  The tutorial mentions Arduino, but then speeds away without ever commenting on the boards.

Oz

Christopher Vaughan

Hey Oz, i too like Arduino over basic stamp. They are much easier to flash. I don't see any advantage to a stamp over the arduino. as for the servo shield remember the arduino only supports up to 13 (with some hacks) per board. you must supply the power voltage separately for the servos and the arduino must be tied to the ground of the servo power. I found it much easier(and cheaper) to simply wire up a power bus for the arduino on some breadboard with header pin fittings for the servo.

Christopher Vaughan

sure let me draw one up in fritzing for you i'll post it tomorrow or the day after.

Christopher Vaughan

Hey Oz, so this is a DC power bus. It is a pretty simple thing to build. I did not include the code because you would just use straight processing code for it see http://playground.arduino.cc/Learning/SingleServoExample for a tutorial. 

You might have to multiplex the servos if you make a custom shield (for space the bus might end up being parallel instead of serial), but this will get you up and running so you understand a  dc power bus.

David Boccabella

One servo board I really like (and I have looked at a few) is the Lynxmotion SSC-32.

The advantage of this board is that you can control the SPEED of the servo's.

i.e.  Is one servo is at 90o and another is at 60o and you want them both to finish at 110o - you can tell the SSC-32 to move them so that BOTH servo's will finish at the same point at the same time. So that the first servo will move slower than the second.

This is great if you have saved a hold sequence of servo movements on an SD card and have time sliced the movements. You can then read and send the movement to the SSC-32 every timeslice and the animatronic unit will then give a constant fluid movement.

David Boccabella

With the timeslicing concept. Think of a graph with the X axis being time and the Y axis being servo positions.

Now draw the movement position of the the first servo. It should look like a curved line. Now do the same for the second servo, and the third etc.

Now decide on a time slice. I use 250ms for mine but you can make it longer or shorter to suit. At each time slice point read the servo position values and store them.

Now when you replay the positions to the SSC-32 you read each set of movements and add the Time command to the instruction string. The SSC-32 will now move all of the servo's from their current positions and finish with them at the new position in 250ms. By then your controlling processor can do a lot of background work including getting the next set of movement and sending them to the SSC-32.

Remember that the SSC-32 cannot force the servo to move faster than the servo was designed to move. With fine tuning you can do a lot with this system.  Lynxmotion already has sequencing software that you can use and as they store the information in MS Access table format it's easy to extract it for other uses.

Hopes this helps
Dave

David Boccabella

Oh - Lynxmotion has several humanoid robot models that can walk and move - so fluidity and handling several servo's all moving at the same time at different speeds is a big part of that.

Oz Stevens

Excellent advice.  I don't suppose you would be interested in sharing design and code data?

Oz

Oz Stevens

Christopher, you are a (bat)man amongst mortals. I'm designing up the body of "the critter", then the sculpt, etc.. Thank you so very much for the help and I will keep stuff posted.

Again, so glad I got the annual subscription.  Just about everything I need for the build is in these tutorials.

Oz

Oz Stevens

That sounds pretty impressive. Especially since I need my critter to be rather fluid. Like human fluidity.