Help with research project in mechanical engineering (motor controlling)

Using Arduino Project Guidance
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Hello all potential Arduino experts. :slight_smile:

Short introduction: My name is Lasse Jakobsen. I am a PhD student at DTU (Technical University of Denmark) and my research is related to tribology (friction and wear) of footwear, with the aim of reducing the occurrence of slip injuries and some sports injuries.

We have created a portable mechanical test device, which is intended to be operated in the “field” (work environments and sports arenas). However, I am no expert in motor controlling, but I have been told, that an Arduino may do the job.

I would very much appreciate some guidance regarding the choice of hardware components and potential setup solutions. Specifically in relation to force measurement and regulation of motor velocity.
I have attached a few illustrations of the setup and hope that it makes sense.

A 18 v drilling machine is used as a rotating motor, with a rubber-covered disc mounted in the drilling head. The rubber-covered disc represents a shoe outsole and is in contact with the floor. The drilling machine is mounted in a cage with a universal joint, making it free to rotate vertical and horizontal. When the rotating disc meets the floor, the cage with the drilling machine will turn horizontally (left or right, dependent on the rotating direction of the drilling machine) and the cage with the drilling machine will touch a force sensor, mounted on a beam. The force sensor will provide a horizontal force (friction force) and should ideally be able to measure in the range of 1000-1500 N.

We need the motor in the drilling machine to rotate with a constant velocity, independent on the amount of applied load (weight plates), materials attached to the rotating disc or type of floor. Hence, if the motor rotates with 10 rpm before the disc comes in contact with the floor, it should regulate the current, thus the motor still rotates with 10 rpm when the rotating disc comes in contact the floor (when the resistance increases).

I would imagine that we need an encoder or tachometer to determine the rotating velocity of the disc, which will provide an input for the motor (through an Arduino) to regulate the current. However, I am not sure which kind of sensor (encoder or tachometer) will be suitable for this application?

Lastly, we need a force sensor, which ideally can log force data synchronal with rotating velocity and time.

I hope the above makes sense. Otherwise, I will be more than happy to elaborate or explain further to any kind person, who may be able to help us.

Best regards
Lasse Jakobsen

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Drilling machines include speed control. If that control is not strong enough for your purpose, you have to design a better controller.

For speed feedback an encoder allows for faster recogniition of changes compared to a tachometer.

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One possible method of measuring the speed of the drill is to paint black and white stripes on the drill chuck (or possible the attached disk) and measure the transitions from black to white with an optical sensor module. Maybe 4 black and 4 white stripes is enough (depending on how slow the drill is rotating).

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How about a purposely built rotary encoder such as these

https://www.mouser.com/Electromechanical/Encoders/_/N-39xfc

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If a drilling-machine and a self build rpm-control will be perfom good enough depends on your needs how big the deviations from the setpoint is allowed to be.

If your motor is allowed to re-gain the rpm of the setpoint in 2 or 3 seconds it will surely work.
For a much higher perfomance I would recommend a professional product that can be bought of the shelf with a high sophisticated speed-control that is included with the motor. This type of motor is called servomotor.
For high performance you need a PID-control
(PID = proportional-integral-differential) with a speed-control and acceleration-control that are "stacked on each other"
Developing such a device is a Ph.D master on its own.

I'm not an expert of how much perfomance you can achieve with an Arduino in this field.
You should ask and research for servomotor-control-projects.

What will be the maximum torque that can occur and what will be the maximum rpm that can occur?

JMC is a company that has servo-motors of different torque with a good price/perfomance-ratio.
The PID-parameters can be adjusted.

best regards Stefan

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6v6gt:
One possible method of measuring the speed of the drill is to paint black and white stripes on the drill chuck (or possible the attached disk) and measure the transitions from black to white with an optical sensor module. Maybe 4 black and 4 white stripes is enough (depending on how slow the drill is rotating).

I think that Idea coupled with a PID (probably just need PI) control system would deliver what the OP needs.

You can use a reflective optical sensor to detect the black and white stripes.

If you print a page with the striped circle on it then it easy to make everything accurate. Cut it out an stick it on the disk

...R

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