You can count the pins on the connector or use a 6mm spanner to remove the back plate to see if it is a resolver.
A resolver is a wire wound device so is obviously different to an encoder, so easy to identify.
If you need to change to an encoder get one with halls as well as the encoder signals so the driver can get commutation.

Quote Originally Posted by paulus.v View Post
Thanks Nick and Gary!

I need to find out if they have resolvers or er encoders. Will I make any damage if I dismantle them to see what's inside? If they are fitted with resolvers, I think I will be able to replace them with encoders.

Regarding the planetary gears, I intend to build a rotary axis and/or a two axis (B/C) head for light wood working and foam. But I thing in either situation there is no backlash allowed. Or am I wrong? At the moment I do not have the money for Harmonic Drives...