Universal motor speeds

[roombacurious]

I was looking at the specs of different tools the other day and was wondering: is the rotation speed (rpm) of universal motors pretty much fixed as is of induction motors?

For example, a router spins at 20,000 rpm, a circular saw at 4,500 and a drill at 2,800. Is this difference just achieved through the use of gears or do the actual motors turn at different speeds?

 

[ivan]

For the full SP you need to visit your local library. In general, motors with brushes will run at high speed especially when unloaded(exactly what depends on design) like router or RA sander. Motors without brushes (induction motors) as fitted to most sawbenches or planers etc run at a multiple of the mains frequency, most commonly just under 3000 or 1500 rpm.

 

[CHJ]

In theory a commutator motor (brushes) with field and armature windings connected in series will continue gaining speed until destruction, in practice mechanical loads such as, cooling fans, gearboxes etc. prevent this. A series motor provides very high start-up torque but must never be run without a load, armature or bearing damage could well result.