Interfacing the Propeller to a Bioloid Dynamixel AX-12+

Dual Exhaust

I can not find the documentation for interfacing the Propeller 3.3v pins to the 5.0v Bioloid Dynamixel AX-12+ servos.

Any help would be appreciated.

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"It is not necessary to change. Survival is not mandatory."
- W. Edwards Deming

parts-man73

This thread http://forums.parallax.com/showthread.php?p=625758

or this thread http://forums.parallax.com/showthread.php?p=653117 might be useful.

Looks like inaki is the go-to guy on this subject.

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Brian

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acy.stapp

Dual Exhaust said...
I can not find the documentation for interfacing the Propeller 3.3v pins to the 5.0v Bioloid Dynamixel AX-12+ servos.



Any help would be appreciated.

IIRC the atmel chip running the AX-12+ and the CM-5 is a 3.3v part. I would guess that you could drive them at 3.3V (but I could be wrong). I'll be trying it myself soon.

Mike G

Hey all,

I have been working on an AX-12 object and I finally made some headway. It was a bit tricky byte I got it working.

I need to do some work on the receiver though. As is, I can't add any more instructions without messing up the bit timing. I welcome any comments or suggestions.

James Long

Mike G said...
Hey all,

I have been working on an AX-12 object and I finally made some headway. It was a bit tricky byte I got it working.

I need to do some work on the receiver though. As is, I can't add any more instructions without messing up the bit timing. I welcome any comments or suggestions.

Mike,

I have a suggestion.....

When you get the AX-12 done, you can go ahead and write the object for the other Dynamixel servos.··· :-)

I've looked to buying some and doing the interface, but never have gotten around to it.

They are interfaced with RS485.

James L

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James L

Partner/Designer
Lil Brother LLC (SMT Assembly Services)

Mike G

James, I was actually seeking help from the community to speed up my receiver code.

But since you bring up this point, this object works with all the Dynamixels since the Dynamixels all use the same command structure. You'll simply need a serial to RS-485 converter check out Maxim and the Dyanmixel manuals.

James Long

Mike,

I was joking, but I do appreciate the information.

I didn't realize the command structure was the same for the rs232 and rs485 systems.

If I get a chance, I'll look through your code and see if I can help.



James L

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James L

Partner/Designer
Lil Brother LLC (SMT Assembly Services)

Mike G

The transmitter works pretty well. On the other, hand the receiver works but I have not come up with a way to determine the end of a Dynamixel response packet. I'm just using a big decrement counter. Unfortunately, when I add one more instruction it throws off the bit timing. I have a couple of ideas that I'll try later this afternoon.

John Abshier

I don't have an AX-12 and have been trying to avoid assembly since a bad experience in a college course in 1973.· But here is a try.· I unrolled the read into 2 parts.· The first part reads the first 4 bytes leaving length in a variable.· The second part reads the rest.

John Abshier

Missed a jump change

receive_header test axmask,ina wc 'C is set if odd parity after AND
if_c jmp #receive 'if C is set jump to receive

should be

receive_header test axmask,ina wc 'C is set if odd parity after AND
if_c jmp #receive_header 'if C is set jump to receive

Mike G

Thanks John

I found an alternative method which works out nicely. It uses byte(4), length, in the response packet to get the remaining bytes of the packet. It only took 3 lines of assembly code and an extra long to do the trick.

1/23/2008 - Oops had a bug.

Post Edited (Mike G) : 1/24/2008 3:10:26 AM GMT