Comparisons of micro-controllers

[aviad]

I've been reading on many sites about different servo micro-controllers, and it seems that there are a variety of parameters to look at when deciding on what type to get. For example, many m-controllers have a "refresh rate"(?) of 20 mS - however, the SSC-32 is running at 1 mS (or am I reading it wrong?)

On the other hand, Acroname has a USB interface for controlling it, while others have RS-232 which is older and sometimes even requires a special cable due to different power requirements.

Another few factors I could see: the number of servos controller, cordless-ness, form factor, available programming platforms...

My question, I suppose, is this: are there a group of very recommended m-controllers, and with that, is there any comparison table made already? I couldn't find one yet.. and for a newbie like me, its hard to create one.

Thanks a lot!

[Joe]

I'm still a newbie myself, but I think I can shed a little light here.

First, don't confuse "servo controller" and "microcontroller." The former is a board dedicated to the task of driving servos, by sending them control pulses at regular intervals. The latter is a general control board, like a mini-computer, which can be programmed to do a variety of tasks. Some servo controllers have a little bit of programmability, and any microcontroller can drive a few servos, but neither one does the other's job well. It's rare to find a single board that is good at both, except those specifically made for for use with Robo-One robots.

Next: refresh rate. I think you must have misunderstood about the SSC-32; there's no way it could refresh every 1 ms. 1 ms is the standard pulse width, IIRC. As far as I know, must servo controllers refresh at pretty much the same rate.

On USB vs. RS-232: I've used both, and I strongly prefer RS-232. You choose your own USB-to-RS-232 driver, and install drivers for it, and you're done; you can then use absolutely any RS-232 device with it, and you can talk to that device with any serial I/O utility, and you can share that device with anybody else who has set up an RS-232 port on their machine. But with USB, every device (in general) needs to have its own drivers, and you can't (again, in general) speak to them with standard terminal software, and you can't give the device to somebody else and expect it to work for them. USB is a big step backwards in usability. The USB devices that suck the least are the ones that have some standard USB-to-serial converter built into them, but then you're paying for that standard converter over and over instead of just once — and you're also lugging it around on your bot even when it's not being programmed. It's pretty pointless. Get an RS-232 device when you can.

In other respects, servo controllers are pretty much the same as far as I'm concerned. I really like the Pololu Micro Serial Servo Controller. It's very tiny, and drives 8 servos for $18, which is a pretty good value. In terms of raw $/servo, the SSC-32 is a somewhat better value. But I really like the Pololu design, and having several of these would let you (for example) have one positioned in the lower torso for controlling the legs, which reduces your wiring (an important factor in a humanoid bot). However, I've heard only good things about the SSC-32 as well; either of these would be a good choice.

HTH,
— Joe

[aviad]

I'm still a newbie myself, but I think I can shed a little light here.

Thanks for a great explanation, Joe!

I'll probably be taking srobot's advice and get a Bioloid with GumStix, as it seems both within my budget and will probably help me get started with the first steps into robotics. However, it seems that the CM-5 is both a servo controller and a micro-controller (or at least, I couldn't find two controllers in the downloaded user's manual so I assume it does both). Will the gumstix board need to do both too? Or is that what constitutes the difference between the gumstix motherboard and the robostix expansion (or maybe this question is for another post..?)

Thanks again!
Aviad.

[JonHylands]

The Bioloid servos don't work the way "normal" hobby RC servos work. You don't need a servo controller to talk to them - they are intelligent devices, and each has its own built-in microcontroller.

If you want to talk to a gumstix at full speed, you will need a USB interface board like the one I sell (http://www.huvrobotics.com), and you will need to buy a gumstix verdex, not a basicx or connex.

Here's a slower speed way to connect a non-verdex gumstix to the bioloid bus: http://www.bioloid.info/tiki/tiki-index ... ge=gumstix

Note that the speed difference is almost 10x slower using this technique.

The board I sell will allow both your PC and your gumstix verdex to communicate to the devices on the bus at full speed (1.0 Mbps). Alternatively, you can build a board yourself - the way it is hooked up is fully documented on this forum.

- Jon

[aviad]

If you want to talk to a gumstix at full speed, you will need a USB interface board like the one I sell (http://www.huvrobotics.com), and you will need to buy a gumstix verdex, not a basicx or connex.

Here's a slower speed way to connect a non-verdex gumstix to the bioloid bus: http://www.bioloid.info/tiki/tiki-index ... ge=gumstix

The link you provided for a slower connection connects between a robostix and the Bioloid, however your solution offers a connection between the verdex motherboard and the Bioloid directly. Am I correct?

Also, with your solution, do I not need a robostix at all (if all the work is done through the verdex motherboard?)

Thanks!
Aviad.

[JonHylands]

The link you provided for a slower connection connects between a robostix and the Bioloid, however your solution offers a connection between the verdex motherboard and the Bioloid directly. Am I correct?

Also, with your solution, do I not need a robostix at all (if all the work is done through the verdex motherboard?)

Yes, that is correct. The new solution does away with the need for the robostix, and allows either a gumstix or a PC/Mac to talk directly to the Bioloid bus at full speed.

- Jon