Small design facts on Electric Motors

Small tips are useful when considering small electrical motors when designing a new product.

• for the same power, the best efficiency of the motor is obtained at high velocities
• Low speed & high torque is obtained via a higher magnetic field, thus requiring a higher load & more wiring
• On the first factor, the price of the motor is proportional to the quantity of copper wiring inside

So from the above:

If your design and users can stand the higher noise due to higher speed rotation and potentially higher friction and heat, always take the higher speed choice you can afford. It will decrease costs, weight & size.

Tip: thanks to the phone industry, the industry has access now to a very high volume produced of micro size motors, initially intended for vibration function of mobile cells.

This vibration is obtained by a small out-off-axis load. Do consider using these motors in your small product designs; not to say that these motors cost pennies only when supplied in the far east.

Typical size: dia.=4mm & lengh 10mm but smaller version with lengh <5mm exists

A great design example using such motors

See the directory for online tools for motor dimensioning, the trade-off always being to use a gearbox and the smallest motor possible, or a bigger motor actuating directly and reducing complexity. From the Tip above, in some cases, the recent solution is to put several motors (ie one per function, like one per wheel)