Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: ProjectM on December 08, 2016, 05:34:48 AM

Title: Motor Controller Configuration
Post by: ProjectM on December 08, 2016, 05:34:48 AM
Hi everyone,

With a group of students we are building an exoskeleton for paraplegics. I am part of the Software & Control department and we are designing the motor controller configuration. We have several requirements:


While exploring several off-the-shelf possibilities, we came accross the Elmo Gold Twitter(http://www.elmomc.com/products/gold-twitter-servo-drive.htm) and the IOMI Pro(http://granitedevices.com/wiki/IONI_device_model_comparison). One of the problems of these boards, is the amount of absolute encoders that can be connected. Both the Elmo and the IOMI board can either have 1 or no absolute encoders connected.

We came op with a solution, so that we are able to connect multiple encoders. In our exoskeleton we are going to use an EtherCAT Master-Slave configuration. The High-Level control (e.g. state-machine) is on the EtherCAT Master and sends joint angle setpoints. Our idea is to use a EtherCAT Slave as a sort of second controller, which gets the joint setpoint and the joint encoder values, calculates the motor setpoint and sends this out to a certain off-the-shelf controller like the Elmo Gold Twitter or the IOMI Pro.
(http://i.imgur.com/xQfRlHQ.jpg)

My question is the following: Is this even a good solution? And what are other solution to this problem? Are there even better alternatives for a motor controller? Might it be a better idea to build and program your own motor controller? (please bare in mind that we have limited experience in that area)

I thank you all in advance for your reply!

Cheers!

Nathan
Title: Re: Motor Controller Configuration
Post by: hadiesper on December 16, 2016, 01:57:28 PM
I am not very knowledgeable about ethercat but I could speculate that the code to manage/run such a system would be relatively simple (measure -> formulate -> actuate). Feedback signals from encoders are also easy to read so I don't see why you can use a simple controller and a custom electronics circuit to drive the motors. This is the only way to keep the size to an absolute minimum.

I would also think that the power requirements below are not realistic, you should typically use much much lower wattage system that has an incredibly high gear ratio to give you the torque you need. Otherwise your power bank and electronics power handling requirements would be unrealistic.