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View Full Version : [Question(s)] Controlling lots of Imperial servos on a Dark side robot?



Slugman
01-10-2012, 09:57 PM
Since I am well on my way to getting that $%^&* hand finished, I might as well try to work out how I am going to control all those servos!
As background info, I have a Robotis robot (Dark side) using an Arbotix on a 3s Lipo, but want to connect more digital micro hobby servos (Imperial Rebel scum) than the Arbotix will allow. The hands are the obvious reason with 7 servos each, but I can think of a number of other uses for servos where a 9 gram micro-servo would suffice instead of a 55 gram AX-12. The weight penalty of a separate board would be quickly offset by the 44g difference for each extra servo that I add.

I did look at the SSC-32, but that would need yet another separate battery due to the different power voltages, which I want to avoid. I am therefore looking at the Seeeduino Mega, which is probably overkill with the number of I/O's available, but I think the little Uno would be maxed out if I end up with two hands on the robot - I.E. If I get swap out the Airsoft left arm & put a second hand on instead.

Does anyone have a better idea on how to control a 'large' amount of digital hobby servos using an output from the Arbotix?
(By 'large' I mean up to 20, but at least 16) I have not found any sort of smaller break-out board that would do it, but that may be because I'm just not looking in the right place. Note that I will still finish off the hand design anyway as the Arbotix will control one of them, but I have delusions of megalomania which involves the use of two robot hands + a couple more micro servos.

I'm open to all suggestions. :confused:

Gertlex
01-10-2012, 10:56 PM
Don't you need to have a separate power supply of some sort for the lower voltage digital hobby servos? I'd assume an Anyvolt or some such (I don't have one of these) to regulate down to 6V. This would still allow one battery to be used.

I think what you can do is use the Arbotix's UART to communicate with two or three of these http://www.pololu.com/catalog/product/207. You can daisy chain them to do up to 128 servos with one UART. They should run on 5V, which the Arbotix can supply via its 5V regulated headers.

Slugman
01-11-2012, 12:26 AM
Thanks for that, I will have a look at them. :happy: The servos I'm using are 5 volt, so I'm going to use the 5v output from the Arbotix to power them unless someone tells me not to. They are tiny, with little current drain, so I am pretty sure the arbotix can power them all. I am trying to limit myself to just two batteries - A 3s for the robot, with a small separate battery for the Axis camera. With a little luck or complicated wiring, I can use the 5v headers for everything connected to the micro-servos.

Gertlex
01-11-2012, 01:31 AM
The servos probably will be fine at 6V, as well, unless they're indeed special. But 5V should be fine of course :)

What voltage is the camera?

Slugman
01-11-2012, 04:15 PM
Camera is an Axis M1011-W - 5 volts, but I'm running it off a NiMh 4.8v 800mAh Batt, as I vaguely recalled somewhere that it was better to use a separate battery for some reason that escapes me now. Actually now I think about it, it seems strange as to why I did that, but the batt is not quite right for the camera, so I must have had a reason - Just not sure if it was a good reason or not.

I had a look at your link, & that looks like exactly what I need - Just an extension for a few extra servos. Thanks for that! :happy: I didn't want to have a separate brain just for wiggling fingers, & weight is always an issue of course.

Gertlex
01-11-2012, 04:52 PM
It may be that the warning you're thinking of is problems when powering stuff with a switching regulator... But I do that with my Trendnet wifi camera, and have no problems.

For an overall power solution, what you may be able to do is have one battery, power the dynamixels and arbotix, then have switching regulators (e.g. these small ones (http://www.mouser.com/search/ProductDetail.aspx?qs=uJpRT2lXVNXJP%2bo08dQqJQ%3d% 3d) which I use) to get the 5V for the hobby servos, camera, and servo controllers.

Slugman
01-11-2012, 09:09 PM
Thanks yet again! That looks like a much neater & lighter solution than lugging around another battery, & from the manual for the pololu it looks like I can also power it directly from the 3s Lipo, so I only need two switching regs if I run out of 5v outputs from the Arbotix - One for the camera & one for the servo power through each pololu I use, as long as I check that jumper switch so I don't join the 5v to the 11.1v together through each pololu. I will probably get a couple of the Pololu's, but I'd better start working on a wiring diagram once the hand design is complete or I'll lose track of what I've done & why. I must be still on the steep part of the learning curve. I hope it starts to flatten out soon.

Slugman
01-13-2012, 01:29 AM
I just ordered three servo controllers. I thought I might as well get them now since I dropped the final CAD design of the hand off to the laser-cutter this morning. He'll make the revised hand parts & I should get them by mid-next week. Yay! :happy: It's kinda like Christmas all over again.

Gertlex
01-13-2012, 06:25 PM
I just ordered three servo controllers. I thought I might as well get them now since I dropped the final CAD design of the hand off to the laser-cutter this morning. He'll make the revised hand parts & I should get them by mid-next week. Yay! :happy: It's kinda like Christmas all over again.
Def know the feeling... I've got a batch of carbon fiber parts getting waterjetted next week, along with an order of stuff from McMaster :)