I would like to formulate how much load can carry for the magnetic actuator used in RC airplanes. Example photo:
enter image description here

It consists of a coil and a magnet. And works according to lorentz force principle.
The torque exerted by the magnetic field on the magnet is directly dependent on the strength of the magnet, the number of turns on the coil, and the current through the coil. So to increase or decrease the torque, we need to either get a better or worse magnet, wind more or less turns, or increase or decrease the current. How can formulate it? Like
Torque = current x magnet property x turn of coil
2 N.cm = 0.1mA x ? x 340 turns (numbers are only example,not real)


1 Answer 1


The torque is linear in the coil current and the magnet's magnetic moment, so torque = current * magnetic_moment * coil factor.

It's easy to measure the current accurately.

It's possible to track down (using your favourite search engine) an approximate formula for the field strength versus current for a coil of N turns, given the number of turns and dimensions. It's easy to measure the dimensions, it's not so easy to count the turns if you didn't wind it yourself.

It's not so easy to measure the magnetic moment of the magnet in your actuator directly, at least not in an accurate way.

With so many things being difficult to measure, it's best to simply measure the torque versus current curve for your actuator, plot the results on a graph, and fit a straight line to it for your_actuator_factor. Then use the formula torque = current * your_actuator_factor. This empirical factor sweeps up all the uncertainties / difficulties in coil dimensions, number of turns and magnetic moment.

  • \$\begingroup\$ how to measure torque exerted by rod on magnet? \$\endgroup\$ Jun 10, 2019 at 10:33
  • 1
    \$\begingroup\$ You measure the torque exerted by actuator on the thing it's actuating. The easiest torque load to use is a rod under gravity. Weigh the rod, measure its length, assume all the weight acts through its mid point, fix it to the actuator. Increase current until the rod becomes horizontal. \$\endgroup\$
    – Neil_UK
    Jun 10, 2019 at 13:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.