View Full Version : ax-12 motors voltage?

05-01-2012, 01:48 AM
Hello, I have a quick problem. I'm trying to connect 4 ax-12 motors together. However I don't think there is enough power to power all 4 motors at 10v. I can power up to 2 motors only. How much voltage should I give to be able to power 4 together?

Or do I HAVE should I split it into 10v for 2 motors each? I would perfer not to do this option

Also these motors act in parallel when connected?

Any suggestions in what I can do? I don't want to blindly blow the motors somehow.


05-01-2012, 02:06 AM
What batteries are you using? Voltage isn't the only consideration, you also need to look at the current your batteries are capable of providing the motors with.

They're being daisy-chained and are thus in parallel, so I'm not quite sure what you mean by splitting them into 10 V for two motors, unless you're talking about two separate power sources for each pair?

05-01-2012, 02:27 AM
I'm using a output power supply for testing. So I'm sure the voltages are stable.

Quick question then, because I connected them in a daisy chain of 3 motors, and then I used the "Write Data" to write to one motor, and it moved!

But when I used "Reg Write", to move only 1 or more motors motor, none of them moved.

05-01-2012, 02:35 AM
What's the maximum current your power supply can provide? Same observation still applies, if you can't provide enough current to power all four motors, not all four will work.

Check the manual on the Dynamixel website for what the different commands do. Reg Write just stores the instruction and requires an action instruction for it to be executed.

05-01-2012, 06:04 AM
Yes, I'm familiar with the manual. Just not on the specifics regarding timing. Say for "Reg Write", how much alloted grace time do I have between the next Reg Write , and the final action command? What is a good current for the motors? I'll hook up the voltmeter to check the current for now.

05-01-2012, 08:29 AM
Not sure about the time, I'd say until power is lost or you overwrite the old command?

According to the specs, the AX-12 draws 50 mA when on standby and up to 900 mA. I presume that you're just doing bench testing, so if you move the motor with no load the current draw shouldn't rise too much above that. I'd recommend also setting the motor to a position and trying to turn the horn manually to get a feel for what an acceptable load is.

Oh, no offence but I just want to check, you meant multimeter and not voltmeter, right? In either case, if you have two meters I'd recommend measuring both voltage and current. Not so important if you have a beefy enough power supply, but if you're straining it (or when you switch to batteries) it'll be very informative to watch how the voltage varies with the load as well.

05-01-2012, 08:39 AM
Why are you using Reg Write at all? It requires you to first send data to the various servos (which may or may not immediately end any previous movement), and then later send a second packet to make the servos so anything at all (don't think there is any maximum time limit). If you need to control multiple servos simultaneously, use Sync Write. Much easier and faster than a bunch of Writes/RegWrites, but with the simultaneous execution of the RegWrite when the packet's checksum is verified.

The very well regulated 12V SMPS from Robotis is capable of sourcing 5A. During attempts to use a 0.4A 12V supply to power an arbotix and only a single servo, I could not reliably use PyPose as the servo would frequently fail to communicate. If you are having lots of problems, remove some of the servos from the daisy-chain and try again. If it starts working, you probably want to try a different power supply with a higher current limit.

05-01-2012, 10:16 AM
I was using Reg Write to try and and move several motors at once, but resorting to just using the write command for moving one motor. What is a good amp reading for 3 motors? Currently I'm getting about .1 amps, but the when I write to the 3 motors nothing happens. However if remove 1 motors, the other two motors kick into action.

05-01-2012, 01:06 PM
Read up on sync write. It was designed specifically for writing an arbitrary number of bytes starting at a single register table address to as many servos as can be placed on the dynamixel bus. If the AX-12 manual doesn't explain it well enough, there are a few threads here and on the robotis qna (http://www.robotis.com/xe/82524) that explain it in a bit more detail.

The AX-12 can pull nearly 1 Amp at full load. If they start working immediately after you remove a single servo, and that servo was not conflicting with the ID of any other servos, then it's quite likely that the servos are pulling just a little too much current for the power supply to handle.

05-01-2012, 02:53 PM
Thanks, for all the help. Your suggestions are correct. because when I reduced the voltage, I can get up to three motors working. I will trying working on Sync. For now We have our program relaying angle coordinates to individual motors and it seems to be working fine.

Thanks for all the help Tician!