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- Pancake Motor Current 1 - Initial Measurements

Note:  This article was published on the interim web site on 6 May 11.  Since we have so many new folks, and so many "old" folks back now, I decided to republish, and start a new dialog in this area.

Just before we went "stealth" I made some armature current measurements on an A/FX Chassis.

Here is a plot of some of the data.

 

 

The pink (magenta?) line is from the laser tachometer.  For every two cycles of the tachometer, the motor makes one revolution, so what the image above represents is just a little more than one revolution.

The blue line is the current, as measured by an inductive ammeter.  The actual value of the current is not important in this discussion.  The interesting part is the variation in current during the different segments of the pancake motor propulsion cycle.

The second image shows a representation of 60-degrees (1/6 of a revolution) of the pancake propulsion cycle. (I think that was Big-T's annotated armature photo.  Thanks!)  You will notice that the resistance value (these values are calculated, not measured) changes during each segment of the cycle. This is based on my assumption that for a few degrees of armature rotation, a brush bridges the gap between two segments of the commutator, putting two windings in parallel, and changing the DC resistance of the motor circuit.  It remains to match the cycle phases to the data.  I expect that this will require accounting for the inductance changes, and the effects of the magnetic field generated by the permanent magnets. 

More to come!

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Comments

colin's picture

What is the measurable effect of a brush "bridging" arms on the armature? Is there a definite deceleration or braking effect and does this make the case for orientating brushes and profiling them to ensure that they do not bridge between arms?

If only my car accelerated like my T-Jet!

tabco's picture

I never got back to additional detailed measurements of the pancake armature.  I suspect that bridging reduces mechanical wear on brushes and the commutator, and allows the motor to run smoother at low RPM by providing a transition from one motor pole to the next.  It also reduces the chances of stopping on a "dead spot" on the motor.  I suspect that there may be more torque available without bridging, but it would probably only be of any benefit at performance extremes, such as drag racing.

I continue to look for methods to model these 3-pole motors.  That would make it much easier to explore the extremes.

Mikey Guindon's picture

If you think about it and try not to bridge the motor poles, the motor probally wont run or run really slow. That would be like pushing the brushes down real far in the chassis, like we did as kids trying to make the motor spin easier. Most of the arms dont ohm out the same on the motors usually, very seldom I have seen a motor ohm out the same in stock form. I have even taken all the wire off the arms counted the turns, I have counted 270 to 319 turns on the arms and put back 280 on each arm and still get different ohm readings. And this is on the older stuff, I doubt you would get any better from the new AW stuff. Orientating the brushes might help, but I think you would get more from finding a way to balance the armature and find a way to keep the middle gear from jumping around and not vibrating, because of the different ohm readings you get between the arms. On some of the newer cars like the mega g cars you can move the end with the brushes in it to change the timing which will change the power band for torque or top end speed, on small tracks you dont notice to much you see it more on the long straights of bigger tracks. On the pancake motors you dont have that option, you might be better off leaving the brushes alone and getting a better armature and put stronger magnets in and let the controler  and the transformer do the braking. Just my 2 cents worth.

Mikey Guindon

colin's picture

Interesting point, non bridging would cause the motor not to start but assuming it's running bridging would have a drag effect, on the subject of wire lengths for motors and reisitance I have the following article which covers it off fairly well:

 

 

How to Rewind Slot Car Armatures

Here's some instructions from Simco covering the basics of rewinding slot car armatures.

Simco Electro Mechanics, Paramount California

Simco Electro Mechanics, Paramount California

 

 


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Purpose

To answer the ever-increasing desire of slot racing enthusiasts to rewind their own motor armatures, SIMCO PRODUCTS now provides the following guidelines to armature rewinding.

Without considering design factors other than the armature winding, motor output may be increased by increasing the ampere turns of the armature. This is usually accomplished by increasing the wire size and decreasing the number of turns thus decreasing the armature resistance. The voltage rating of a motor may be approximated if the armature resistance (measured in ohms) is known. Armatures of 1 ohm or less are usually rated at 6 volts and 2 ohm armatures are rated at 12 volts.

Since armature size and design varies with each different type of motor, no attempt is made to give specific turns data. Instead, convenient charts are provided to give the approximate number of feet of wire required for each motor winding for any desired armature resistance. Wire size used will vary with different armatures, as a general rule try increasing the size by two or three numbers (3 numbers double the wire size) ie. if the original wire size was AWG 34, try AWG 31 or 32.


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Feet of Wire Required for Each Armature Winding

Before removing the old wire, mark the position of the commutator in relation to the armature segments so that they may be realigned if they are moved during the rewinding process. Determine the armature resistance desired and select the wire size and length from the tables of (figure 1) for three pole and (figure 2) for five pole armatures. 

Simco Wire Gauge Chart

Simco Wire Gauge Chart

 


While winding the first winding count the number of turns used and record for reference while winding the balance of the armature. Wind the armature using a tight even pressure, but not so tight that the wire is stretched or broken. After removing the old wire, insulate the corners of the armature segments with electrical tape or other suitable material Select the new wire size and length and follow these step-by-step instructions.


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Three Pole Armatures

Figure 3

Figure 3

(Refer to Figure 3)

1.     Solder the wire to the commutator at point A. Use care in soldering so that the commutator is not damaged. Start winding the wire inaclock-wise direction around segment 1. Wind on the total amount of wire as determined from the wire table. Count the number of turns used.

2.     After the first segment is complete, solder the wire to point B. (Note: SIMCO PRODUCTS 200 SERIES WIRE MAY BE SOLDERED WITHOUT STRIPPING.) Continue winding segment 2 in a clockwise direction. Wind segment 2 with the SAME NUMBER OF TURNS as segment 1.

3.     After segment 2 is complete, solder the wire to point C and continue winding segment 3 in the same manner.

4.     After segment 3 is complete, solder the wire end to point A.

 


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Five Pole Inline Armatures

Figure 4

Figure 4

(Refer to Figure 4)

1.     Solder the wire to the commutator at point A. Start winding the wire in a clockwise direction around segments 1 &2. Wind the total amount of wire as determined from the wire table. Count the number of turns used.

2.     After the first winding is complete, solder the wire to point B. Continue winding segments 2 & 3 in a clockwise direction. Wind segments 2 & 3 with the SAME NUMBER OF TURNS as segments 1 & 2. After segments 2 & 3 are wound, solder the wire to point C.

3.     Wind segments 3&4, 4&5 and 5&1 in the same manner, advancing in the counterclockwise direction with each new winding.

4.     After all segments are wound, solder the wire end to point A.


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Five Pole Sidewinder Armatures

(Refer to Figure 4)

Wind sidewinder type armatures in the same manner as inline types except start by soldering the wire to point E. Wind segments 1 and 2 in a clockwise direction and solder the wire to point A. Continue winding in the same manner as inline (motor) types, advancing in a counter clockwise direction with each winding.

 

 

If only my car accelerated like my T-Jet!

colin's picture

If only my car accelerated like my T-Jet!

colin's picture

If only my car accelerated like my T-Jet!

Mikey Guindon's picture

Good info, slotmonsters.com is a good site to get info from.

Mikey Guindon