How To Rewind Your HO Motors

How to Rewind Your HO Motors

By: Edward Biachi

  Rewinding a motor for a 1/32 or 1/24 scale car can be a tricky job. Naturally it would follow that rewinding, the motor of an HO scale car should be slightly impossible.
  

  Not quite, For most HO motors this is true, but only because the tiny commutators generally used make wiring very difficult. The Aurora Thunderjet motor, however, due to its “pancake” design is easily wound and wired. The armature has large, flat pole pieces and an even larger and flatter commutator. The commutator is even more easily wired than any of the large scale’s conventional commutators.
 

  The rewinds themselves preform beautifully on a reasonably fast track. They accelerate just as a stock car, but they have a much higher top speed. Long straights are “ home sweet home “ to these motors. On a large, fast track they cannot be caught. Low speed performance is good and braking does not suffer at all. Power brakes will actually work better.
  

  To make things still easier on you, a rewinding machine is easily made for these motors. I suggest that you make and use one of these machines. The machine will rotate the pole so that you only need to feed out and guide on the wire while you turn the crank. The machine is most easily built from parts from a Gilbert Erector Set and a length of 3/32-inch o.d. brass tubing ( see pictures 3 and 4 ). The bent pieces of tubing fit over the ends of the armature shaft and are held tightly over it by a rubberband. The tubing and the armature are mounted on the end of a crank ( see pictures 3 and 4 ). One pole of the armature can be lined up with the axis of rotation of the crank and be wound and then another pole moved into place.

  Remove the body from the car you intend to rewind and set it aside. Pry the copper spring clip off the chassis so that you may remove the gear plate. With a screwdriver carefully pry off the armature pinion gear ( see picture 2 ) and remove the armature from the gear plate.

  After studying your armature and picture 1 to identify the commutator and commutator tabs, pry back slightly on one of the tabs with a small screwdriver and pull the commutator free. Pull the commutator from underneath the two other tabs if necessary . Now gather up all your courage. You are going to have to break every one of those tiny wires leading to the commutator. Once that is done there is no turning back. Make sure that no loose ends remain on the commutator and lay it aside in a safe place.

  Pick up the rest of the armature and study the windings, Notice that they consist of separate poles, each wound exactly the same. Also notice how neatly the armature was wound. Although your new wind does not have to be wound extraordinarily neatly, a neat wind will work better than a sloppy one. In racing every bit counts.

  Take the “ finish” wire of each pole and wrap it twice around the soldier lug directly to the left of its pole as you would see it looking end on at the pole with the commutator side of the motor down. Then wrap the remainder of the wire around the armature shaft. This serves the double purpose of holding the wire tight around the solder lug for soldering and getting the ends out of your way. Similarly, take the “ start” ends of each pole and wrap it around the solder lug to the right of its pole. Then wrap it around the armature shaft.

  Using a soldering tool, solder the connections using electric quality rosin core solder. After the solder cools file down the excess solder to a minimum, taking care not to cut the wires. Otherwise, the excess solder may rub against the bottom of the motor casing causing a loss of power and possibly overheating. Unwind the excess wire from around the armature shaft and cut them off at the solder lugs.

  The armature is now finished. I do not recommend coating the wires with epoxy as they are safe without it and the epoxy will trap heat. However, it would be a good idea to balance the armature if you can rig up the equipment necessary. If you measured the wire you used very carefully and wound it on evenly, the armature should be reasonably balanced as it is.

  You may now put the armature back on the gear plate assembly and replace the armature pinion gear. It may be wise to install a new armature pinion gear because the old one may start turning free of its shaft causing power loss. The new gear only costs 10c. you can use an X-acto C-clamp to press on the gear. Other types of C-clamps will do only if they push on the armature shaft, not the armature itself. Pushing on the armature could cause the armature to break its bond with the armature shaft hence allowing it to turn free of its shaft. This as you might guess is no way to win the championship.

  There are disadvantages to rewinding and these should be discussed. If you use either of the winds described in this article you will need a 30 or 25-ohm controller for use with the rewinds. Tower Engineering, Russkit and Cox all make fine controllers in this range. The Tower-Star R-30 costs $5, the Cox Mark III costs $7 and the Russkit costs $7. There is a good chance of being able to buy these controllers much cheaper from someone who races 1/32 or 1/24 scale cars as they have become far too tame for the motors currently being used in these scales.
As mentioned before, heat may become a problem with the #36 wind. Excessive heat means something may be shorting or rubbing. To help keep the motor cool, cut away part of the motor casting just to make sure you do not cut the portions which keep the magnets away from the armature.

  A rewound motor draws more amps than a regular motor, which places abnormal load on the pickups and commutator brushes. This makes the use of Arora’s Silver-plated pickups and AutoWorlds Hi-Silver or Hi-Copper commutator brushes quite desirable. The silver-plated pickups do not oxidize as rapidly as the stock pickups and will not require cleaning. The AutoWorld commutator brushes reduce electrical resistance and will not generate as much heat as the stock brushes. Since they are not made of carbon, they will not leave deposits of carbon on the commutator. The Hi-silver and the Hi-copper brushes cost 29c and 19c a pair respectively . The silver plated pickups cost 25c a pair.
If the rewound cars noticeably slow down the acceleration of the cars in other lanes, the track needs more power. An extra power pack wired in parallel ( see photo 5 ) will supply the needed power. You will still be running on 18 volts, but you will have greater supply of amps than before.