# 2-DOF Robot arm for aerial manipulation

Hi there!

I’m happy to write my first post here. The reason is because I’d love to hear your suggestions and recommendations for the motor configuration I need for my project. Let me first do a brief summary of this project.

This project is encompassed within the context of my PhD: I am doing research in the field of aerial manipulation, i.e. a multirotor with a robot arm attached to it. More precisely, I am in the field of optimal control & trajectory generation: solving the problem of what torque do my motors must apply so robots perform a desired trajectory.

So far, all robots existing for that aim consider arms with Dynamixel-type motors. The problem with this kind of motors is that you cannot torque-control them. And this is why I came up with ODrive and BLDC.

I am gonna do a list of important issues to have in mind when selecting the motors:

• Light-weight is crucial. The whole 2DOF manipulator cannot exceed 500g of mass. So I was thinking of a motors weighting max. 100g each.
• The links length is gonna be small. I am thinking of 100mm each. Since it is for research purposes the max. force done by the end-effector is not that important. I’d say that it could lift 100g in the worse-case configuration. That means a torque in the first joint of 0,2Nm aprox.
• I expect to add a reduction belt system for each motor of 1:5.
• The motor for the second joint is gonna be placed also in the base so the first one does-not have to lift also the weight of the second motor.
• The motors will be most of the time stalling.

Questions:

• Since my motors will be most of the time stalling, is it better to consider gimbal motors instead of typical BLDC?
• I’d would need absolute position of my motors during all experiments. In case of adding absolute encoders, will I have do some sort of “homing” sequence when starting up?
• I was thinking of powering the manipulator up with 4S battery (14.8V nominal voltage), is that ok?

As I said before, I’d love to hear you recommendations for the motors. I was thinking in the Tarot 4008 motors.

I think this is all I wanted to explain. In case you don’t have enough information or you need a more advanced design, I’ll go back with updated info.

Thank you very much,

Pep

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