View Full Version : [Question(s)] Questions about AX Servos

03-25-2013, 08:31 PM
I'm looking into using some of the AX servos for a project I'm working on, I had a few questions.

Can a horn we attached to both sides of the servo? This is the primary reason I want to use these servos, I always hate to have things cantilevered. If so, were can extra horns be purchased, or would it be easier to make them?

Can these servos be run easily from an arduino or raspberry pi?

How are the servos controlled/is it recommended to use the electronics from Trossen to control them?

03-25-2013, 09:43 PM
Using something like an Arbotix or CM510 or USB2AX is the easiest way to control the servos.

That being said, I've been able to control Dynamixels by tying the RX and TX lines of an Atmega microprocessor (such as Arduino) to the serial bus, each with a 70 Ohm resistor, and a very weak pull-up to 5V. (The built-in pull-ups on the Atmega, which are about 20 kOhm IIRC.)

Beware the Raspberry Pi, though, it uses 3.3V I/O, and if you put in 5V, it will fry. You will need some kind of bi-directional level translator. The easiest way to do that is with a single MOSFET transistor and pull-ups on either end, but a more robust way is probably to get a real board/chip that does the translation for you.

The Dynamixel servos allow you to put "idler" horns on the back. Those horns provide rigidity (thus, no cantilevering) but do not drive the connected assembly. This is why the brackets always double up in a "U" shape -- one end is driven; the other is idling.

03-26-2013, 09:28 AM
You want one of these three brackets: F1 (http://www.trossenrobotics.com/store/p/6179-Bioloid-Frame-F1.aspx), F2 (http://www.trossenrobotics.com/store/p/6180-Bioloid-Frame-F2.aspx), F4 (http://www.trossenrobotics.com/store/p/6182-Bioloid-Frame-F4.aspx); and the bushing/hubs (http://www.trossenrobotics.com/store/p/6327-Bioloid-Bushing-Hub-Washer-Set-10-pack.aspx). With these, each servo needs 4x 2mm bolts, 6mm long, and 1x 3mm bolt, 10mm long. Jwatte is correct that one side is idling, and the U shape makes cantilevering unnoticeable.

07-19-2013, 09:02 AM
In regards to using a Raspberry Pi to control a Dynamxel, I've just finished testing a PCB I've made which translates between a 3.3V to 5V bidirectional bus (though in my case I'm using a different 3.3V system to the Raspberry Pi).
It was based on a high speed I2C buffer (TCA9406), which is ideal for this sort of application as I2C uses a similar open-drain configuration and runs at 1MHz.