We are a group of 3 student working on a robotic hand project. For this project we consider dynamixel smart servos. For this project we will be using around 24 servos for controlling each joint of the hand. Because we are using so many motors we are a little in doubt in how to control the motors, get data and supply enough current for each of the motors without damaging the internals of the motors. We want to be able to monitor the current/torque exerted in the motors while controlling the robot hand with position control. We are pretty new to serial communication and daisy chaning components in robots. And we are doubting that daisy chaining the motors will be able to supply enough current. For example: if we have 24 motors daisy chained with a stall current of (1.5 A - dynamixel XL330), in case of high load on all the motors at once wouldn’t the current running through the motor be too large if we have all running at the stall current?
Are the power supply connected in series or parallel in the internals of the motors when they are daisy chained?
Daisy chaining has the advantage for us of beeing compact and less complex with regard to cable management.
Because of this possible problem we are considering using the lynxmotion SSC 32 U for controlling the motors. Would this be a good option for us? And can we then just use the 3 pins on the motors for control and monitoring the data from the motors? Would this be the optimal option?
@lordrumford Welcome to the RobotShop Community. The Lynxmotion SSC-32U servo controller can only be used to send PWM / PPM signals to RC servo motors. Unless the Dynamxel servos you chose can be converted to an RC mode, they use serial communication and as such are not compatible with the SSC-32U at all. The fact that they both use three wires is not really relevant since the communication and control method is so different.
You are entirely correct to worry about daisy chaining so many servos together as the current through the wires and servo electronics (for the first number of servos) will be very high. Although RobotShop does not carry Dynamixl servos, the Lynxmotion Smart Servos have a solution for this:
The LSS Power Hub allows Lynxmotion servos to be powered along the bus, so (for example) every 5 servos could have their own power supply, while still being daisy chained. You can se if Dynamixel has something similar, or potentially create your own similar solution:
@cbenson Thank you very much foryour fast response!
Okay, so the SSC would pretty much ruin the advatages of the UART-write-read function I can see. That’s good to know.
Yes we have also considered the lynxmotion smart servos but saw that there were no apparent libraries for the motors in ROS. And as we wish to control the robotic hand in ROS, a library would be nice when we have to write positions to the motors and obtain different data such as the current draw/torque, position from each individual motor and so on. For LSS we looked it up on the Lynx website and saw that the libraries for ROS was “coming soon”. So it seems that the Dynamixel motors are the best candidates for the project.
