How to Implement a Physically Human-Controlled Robotic Arm?

Question

I'm a complete beginner in robotics other than FIRST competitions at my school. I wanted to make a robotic arm that works by a person physically moving the end-effector in 3D space and the robot staying in place even when the person removes their hand. Similar to https://youtu.be/RLxIg69GWqA?t=465. The robot arm would also apply force-feedback when it gets close to some predefined threshold.

If I wanted to use servos (because I really need the angle data for force feedback), I would need a certain gear ratio for torque (there is no payload to the end-effector; the only loads would be for all other axes' connections), and this would make it hard for someone to move the end-effector fast and efficiently.

To offset this problem, I have found online that I can use force control on the end-effector. The problem with this is that most 6-axis force/torque sensors are seriously expensive and way too industrial for my needs. I also have no idea how to implement this kind of sensor to the arm.

Are there any simpler ways to accomplish the task above? Any changes/recommendations to how I'm going about this? I plan for this to be a 5 DoF arm with a 16" reach and, as i said before, no end-effector payload.

Answer 1

Fully integrated highly calibrated force torque sensors are complex and priced accordingly. However you do not need that level of precision for your application. If you're willing to do a little bit of electronics yourself you can make your own force feedback circuits using strain gauges.

If they're mounted on or near your end effector you can measure the strain on the link/mount and then use that as your force feedback. It will give you direct feedback on the forces applied to the end effector and you can align them with your primary axes to simplify the math for providing the feedback to your controller potentially. Alternatively you can possibly have one at each joint to provide the feedback necessary.