PDA

View Full Version : [Question(s)] Hi all and some dynamixel info



nagash3
11-01-2009, 07:43 AM
Hi all
I'm new to the forum e new to robotics too, I'm interested in buy some dynamixel to develop a project but I've some dubts about powering it.
I wanna to use either rx64 and 28 anda I wan to power them 18v to the 64 and 16 to the 28 but there is the problem:
can I select the using power from the servo (Theres a functions if I remenber well) using the same power board (smps2) so power the board with the 18v and selct 16v with the servo function of the rx28?
or I 've to power them with to power line one 18v and one 16 v and two board (smps2)?
or again I've to use one board for every servo?
There someone that know where to see a draw/diagrams/picture of a mixed servo system powering?
sorry for my english and thank for the reply byez

MikeG
11-01-2009, 08:24 AM
Dynamixels do not regulate voltage. Dynamixels report max and min voltage thresholds through an alarm.

Setup two Dynamixel segments one with RX64s and one with RX28s. The RX64 segment is powered with 18V and the RX28 segments is powered with 16V. The data signal can be passed to both segments at the same time.

How you go about supplying power is up to you. If you have the 18V source already all you need to do is drop 2V for the RX28 segment. That can be done with 3 diodes in series.

nagash3
11-01-2009, 09:56 AM
thank's for the rapid reply
but can I supply power via the smps2 (18v) to the rx64 segment and than drop down the voltage at 16v for the rx28 in the same line of power or I've to use two different smps2 board?
Is preferrables to use the voltgage for the servos I've much (rx28 i think 14) or the higher voltage (18v for the rx64 but I think I will use only 6 of this)?
how much current will I need for supply power to 14 rx28 and 6 rx64 (I think the max number of them running at the same moments will be 2rx64 and 6 rx 28 the servo specifications say 1,2 A at servo so 9,6 A?
byez
ps
somewhere on the net there's a draw or scheme that show how to power the dynamixel?

MikeG
11-01-2009, 10:54 AM
Like I said, how you power the segments is up to you. You can use as many or few power sources as you feel are necessary for your project.. All that matters is the power source(s) can handle the load.

You should take a look at ohm's law and basic electronics.

Adrenalynn
11-01-2009, 01:19 PM
I don't have any experience with the big Dynamixels. I have decades of experience with the RS-* protocols and interfacing them. So where the rubber meets the Dynamixel road, I can only answer at the RS422/485/232 level:

You can share the signal bus. But you need to cut the power bus and supply independent power to each of those busses. The ground bus MUST be spliced and share a common mechanically-sound electrically common bus. The signal bus is interested in the differential from ground.

Those are motors, so I'd expect my inrush current to be at least 2x. As a general rule of thumb, double whatever the expected power supply rating you expect.

[Edit to clarify and agree with MikeG - how you get the power on that second bus is up to you. Adequately sized diodes, a switching regulator (Like the CastleBEC), or entirely different power.]

nagash3
11-01-2009, 01:44 PM
so you suggest not to use the power board from robotis smps2 but to supply power directly from the battery or the wall power supply (if voltage match)?
I'm going to use the usb controllers directly from the pc and for the first stage of the project I wanna power via ac/dc adapter not from battery
It's difficult to me to explain me because I don't speak well english and i write it less:)
thx for the help and the patience

JonHylands
11-01-2009, 02:52 PM
I'm pretty sure you can run the RX-28 at 18 volts, in spite of what the spec table in the manual says. Andrew is running his big biped, which is a mix of 64's and 28's, and I'm pretty sure he's running them all at 18-20 volts.

The control table on the RX-28 lists the max voltage at 24 volts, same as the RX-64.

I've never used 28's, so I can't say for sure, but I'm sure when Andrew gets around to reading this thread, he'll be able to chime in...

- Jon

nagash3
11-01-2009, 03:41 PM
that's a good news thxs

DresnerRobotics
11-01-2009, 08:32 PM
The RX-28s will be fine on 18v. I use RX-64s and RX-28s at 17v or so on a daily basis.

I've had the RX-64s running at a healthy 22v without issue, but I wouldnt recommend using the RX-28s that high. They might be theoretically rated that high, but I have the feeling they'd get pretty hot.

nagash3
11-02-2009, 10:01 AM
I've found some 19v 7 A laptop wall power adapter what you think about?

JonHylands
11-02-2009, 11:14 AM
I use a 12 volt, 17 amp DC power supply (http://www.commonsenserc.com/product_info.php?products_id=648) to power BrainBot while it is on the bench. That provides power to the Mini-ITX, the AX-12 servos, the track motors, the camera, and anything else I have plugged in.

- Jon

Adrenalynn
11-02-2009, 11:35 AM
Don't AX-12's have a little lower current drain than say something like RX-64's?

Adrenalynn
11-02-2009, 11:37 AM
I've found some 19v 7 A laptop wall power adapter what you think about?


Unless I'm mixing up my threads - you needed 18v @ 9.6A minimum you decided. So you're going to use 19v @ 7A. What do you think about that?

nagash3
11-02-2009, 11:49 AM
cause I'm not to have alla the servo running in my first time I'm gonna buy a part of the servo to test the weight shift (I'm afraid I'm gonna have the same prob tybs have with hagegaka about ankle/hip roll) so Ihave this 19/7 here in my room of an old toshiba and I think to use it for this test and after purchase what I need (18/9.6) but I'm pretty sure there not fixed voltage (18v) wall adapter with such high current 10 amp than I'm alright searching for something that match....

Bullit
11-06-2009, 05:42 PM
I don't have any experience with the big Dynamixels. I have decades of experience with the RS-* protocols and interfacing them. So where the rubber meets the Dynamixel road, I can only answer at the RS422/485/232 level:

You can share the signal bus. But you need to cut the power bus and supply independent power to each of those busses. The ground bus MUST be spliced and share a common mechanically-sound electrically common bus. The signal bus is interested in the differential from ground.


I have to correct Adrenalynn here :cool:
RS485 half duplex for robotis dx, rx and ex servos (dynamixels). RS485 is not ground referenced. It is a differential pair, in this case half duplex. The grounds do not need to be tied together to mix signals from rx-28s at one voltage and rx-64's or ex-106's at another voltage.

The robotis ax series servos use ttl half duplex and is ground referenced.

Adrenalynn
11-06-2009, 06:08 PM
So they must have four wires + two wires - six wires?

Bullit
11-06-2009, 09:32 PM
4 wires total, two for power and two for the half duplex differential pair. Full duplex would require 6 with power.:happy:

MikeG
11-07-2009, 10:26 AM
@Bullit,
For most intents and purposes the RX network is proprietary and a closed system. In a real world scenario RS-485 networks use a common reference voltage at the receiver/transmitter. This guarantees that the 485 transceivers stay within specification.

I'm confident that if you opened up an RX and looked at the transceiver, you would find that the transceiver is connected to power ground.