Measuring Motor Characteristics

[DonRotolo]

As we all heard at Kickoff, Woody has asked the 36 teams who received the National Instruments DAQ device to measure and publish the characteristics of the motors in the Kit of Parts. This thread is being created to discuss just how to accomplish this, and what those measurements might mean in the real world.

There is a good White Paper that discusses the subject in detail, even suggesting an experimental setup. It is good reading.

The drawback to that method is the use of a conventional spring scale to measure torque. It would be better to have some electronic sensor, so all the data can be recorded by the DAQ, but in-line torque sensors like this are definitely NOT inexpensive.

I am thinking of exploiting the characteristic of a spring (including a spring scale - think fishing scale) where the linear movement is directly proportional to force. I will use the setup shown, but measure the force by converting the linear movement of the spring scale to an electrical signal. There are dozens of ways to do this, including linear potentiometers, or just a string and pulley system for a regular potentiometer.

The next issue is reporting the results: What, exactly, would be most useful? I'm thinking of Torque vs Power. Torque vs Speed, and Torque vs Current, all for a few selected voltages ( or perhaps Victor PWM values?), plus stall current and max non-load speed.

Any ideas and comments would be most welcome.

Don

[Joe Johnson]

Originally Posted by Don Rotolo

As we all heard at Kickoff, Woody has asked the 36 teams who received the National Instruments DAQ device to measure and publish the characteristics of the motors in the Kit of Parts. This thread is being created to discuss just how to accomplish this, and what those measurements might mean in the real world.

There is a good White Paper that discusses the subject in detail, even suggesting an experimental setup. It is good reading.

The drawback to that method is the use of a conventional spring scale to measure torque. It would be better to have some electronic sensor, so all the data can be recorded by the DAQ, but in-line torque sensors like this are definitely NOT inexpensive.

I am thinking of exploiting the characteristic of a spring (including a spring scale - think fishing scale) where the linear movement is directly proportional to force. I will use the setup shown, but measure the force by converting the linear movement of the spring scale to an electrical signal. There are dozens of ways to do this, including linear potentiometers, or just a string and pulley system for a regular potentiometer.

The next issue is reporting the results: What, exactly, would be most useful? I'm thinking of Torque vs Power. Torque vs Speed, and Torque vs Current, all for a few selected voltages ( or perhaps Victor PWM values?), plus stall current and max non-load speed.

Any ideas and comments would be most welcome.

Don

All we really need are 2 or 3 points that you measure the following 3 items (all at the same voltage):
Torque, Speed, Current

From there we can curve fit to get The Big 4: Stall Torque, Stall Current, Free Speed, Free Current

Knowing the Big 4 at any voltage, we can get the Big 4 at any other voltage.

The Free data (Free Current and Free Speed) are relatively easy to get, so try to get some data toward the middle of the speed/torque curve if you can since that is where we are going to be operating most of the time.


Joe J.