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HO Racing Tips
by Ted A. Johnson
AURORA CARS
Armature Rewinding
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I prefer to wind my own armatures. Pre-cut
each of the three wires to the same length so that each pole will have the same electrical
resistance. This also assures that each pole will weigh the same, reducing or eliminating
the need for static balancing. It's very difficult to count correctly the number of turns
while winding; unbalanced weight and uneven electrical resistance usually will result.
When winding an armature, it's very important to wrap the wire
straight, not at an angle across the pole. The latter wastes space. Try to completely fill
the available pole area with as much wire as possible.
Contrary to popular belief, No. 35 and No. 36 wire can be used
without encountering excessive heating. True, such armatures may overheat, but the heat is
caused by the extra power needed to overcome drive-train friction. Reduction of friction
will be discussed later. Another cause of armature overheating is weak magnets - the
weaker the magnets, the harder the armature must work, thus drawing more current and
heating up.
I've used 6 1/2 feet of No. 34 wire, which is about all you can
put on one pole. With this wind, however, the slightest excess friction will cause
overheating. The following winds haven't giver me any heat problems: 7,8,9 and 10 feet of
No. 35 wire; and 10 or 12 feet of No. 36. Ten feet of wire will produce approximately 190
turns.
When No. 36 or larger wire is used, some of that all-important
torque is lost. Since the usual HO track is quite short with the longest straight seldom
exceeding 10 feet, you need - within limits - all the torque obtainable.
A stock Aurora T-J, for example, has more torque than is
necessary for the stock gearing. The rewind chosen must be a compromise, producing
sufficient torque but also adding RPMs for higher top speed. A good test is to hold your
car on the track with the rear wheels clearing the surface. Motor RPMs should follow
controller setting - that is, when you depress the controller plunger to "full
throttle", the motor should reach top speed when the controller is full on. If the
motor lags behind the controller, torque is not what it should be.
Be cautious when considering advanced timing. This will increase
RPMs, but it will also reduce torque. With less torque, you may wind up with less
acceleration and lower "flat-out" speed. Experiment with retarding the timing to
provide more torque: It works. |
Magnets
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| Size and length of wire used to rewind an
armature is governed, to a large degree, by the strength of the magnets. With a good,
free-running drive-train, No. 39 wire works well with stock Aurora magnets. With Hong Kong
Aurora magnets, use No. 38 wire; with LaFanke magnets, 13 1/2 feet of No. 37. With Mura or
Arco magnets, you should be able to use 12 feet of No. 36 or possibly even 10 feet of No.
35. The reason for this variation is that the larger the wire, the lower will be the
torque and the higher the RPM. To restore the lost torque, you need stronger magnets.
Also, the stronger the magnets, the better the braking available. |
Pickups
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| When a hot armature and strong magnets are
installed in an otherwise unmodified car, the result won't go worth beans! Electrical
contact between the stock pickup shoes and the track conductor strips is poor, and the
rewound armature can't draw the current required for top speed. There are at least two
solutions. First, you can add silver solder to the bottom of both shoes to improve the
contact. Silver solder wears away rapidly, however, and must be replaced often. For this
reason, I prefer the alternate solution. Use the stock pickup shoes, but stretch their
coil springs to provide more pressure between shoes and rails. With body and weight-pan
removed, these springs should be strong enough to just barely hold the front wheels off
the track. |
Belly Pans
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| Weight pans are a definite "must"
for best car handling, as well s to assure good pickup shoe contact. In my opinion, the
0.032-inch-thick Mura pan is by far the best. In fact, the cars can handle even more
weight in the pan without loss of speed. A 0.050-inch Mura pan would be ideal. One of my
fastest and best-handling cars has a homemade 0.050-inch pan. |
Friction
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Reducing friction is just as important as
installing stronger magnets. A car with too much friction will act as though its magnets
are too weak. If a rewound armature is used, acceleration and speed will be disappointing
and heat will also become a problem.
Excess friction is often caused by the gear-plate being
positioned too low in the chassis, pinching the armature and not letting it turn freely.
To correct this, cut a shim in the shape of a magnet, using match-book cardboard, and
place it underneath the front magnet. This will hold the gear-plate away from the armature
and provide ample clearance. If one shim isn't sufficient, use two.
Friction may be reduced even further by making bushings from
3/32-inch brass tubing and installing them in the top and bottom armature holes, and on
the cluster-gear-assembly shaft.
Axle bushings may also be used, but they aren't as important as
the above. If you do install rear axle bushings, consider raising the center-line of the
bushings to lower the center of gravity and provide better handling. Be sure to consider
weight-pan thickness and rear-wheel diameter, however. |
Motor Brushes
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| In my experience, the German soft brushes
-available from Hobby House, in Monroe, La., - are the best, and should be used with any
rewind. They wear smoothly and produce minimum drag on the commutator, while allowing
ample current flow. With any rewind, increase brush-spring tension. When bending the
springs in, toward the chassis, make sure the leaf spring doesn't get crimped or it won't
hold the pressure. If bent properly, the spring should just touch the corner formed by the
brush hole and brush-spring slot in the chassis. |
Tricks to Try
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I've tried additional modifications, but
they require considerable tedious work. Here are three, if you care to try them:
(1) Install a metal case around
the magnets to equalize the
flux. This helps, but I don't feel it's worth the necessary effort.
(2) Add a third lamination to an
Aurora armature when rewinding. The problem, here, is the amount of work needed to get it tucked into the chassis when the plastic gear-plate is used.
(3) Use a brass gear-plate to
minimize friction. I've found however, that using brass bushings (as
described above) works just as well. |
  
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