Hi Rick, I did the same thing a few years back. You need to pull the armature and clip the leads going to the smaller winding in the field. You will need a piece of coat hanger wire to form a brush holding do-hickey when replacing the armature back into the case. Overall I did NOT see much improvement.
You can get someone (or yourself) to REPLACE the 12 volt field coils with six volt coils, leaving out the shunt as well. I am running this set up now. Not quite a NATS power winch, but close. Launch practicing with this setup is much more like true contest launch. Brent Hoover RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format

