Electromagnetic actuators

This is a continuation of my previous posts about actuators.

Electromechanical actuators are often very simple to work with. You connect them to a controller chip that feeds it with the right voltage, and apply a gearbox with the correct gear ratio to get the speed/torque needed for your application, simple as that. In most cases you just throw in a servo and you are instantly satisfied. They are fast, efficient and accurate.

Regular DC Motor

Stepper motor

Servo motor

Rotary motor encoder

DC Motor with Gearbox

Solenoid actuator

However what bothers me about them is that the motors will continuously pull current from your precious power source. In my project this is a big no-no, since I am aiming for very long power life. One way to avoid this constant power tapping is to use a very high gear ratio or a clutch mechanism that will effectively make the actuator stay locked in place when not active. However this can quickly add complexity and cost to the solution. Another problem with using motors directly is that you need to facilitate the means to get position feedback yourself by either using a rotary encoder or some other 100% reliable sensor. If you use a stepper motor or a servo, you get around this problem, but they are very expensive. Another problem is where to put them. In many small robots, the servos actually make up the limb entirely (as seen in the construction of the excellent A-Pod robot by Zenta), but for my project that is not desirable. I don't want the motors sticking out of the limbs either. I want the limbs to fully contain its actuators in an elegant manner. So electromechanical actuators? Maybe...

Next post will cover the pneumatic part of the actuator spectrum.

--Lennart