Friday, August 16, 2013

Motor Removal

Today I removed the motor from the Electric Booger. It took a grand total of 50 minutes. It was almost like removing a starter from a Peterbilt.
I inspected the motor coupler because there is unfortunately no way to do so when the motor is installed. I just have to trust that everything it tight (and nothing that is not supposed to move is not moving) and that it will get me to work on time.

The good news is that the coupler looks very good. Thanks to the excellent machining work of my friend Matt VanTol, the set screws holding in place were still tight and there is absolutely no abnormal wear on the splines:
Just a bit of rust. Maybe I will put some grease on it when I assemble it this time.

Thursday, August 15, 2013

Motor Direction Reversal And Brush Timing

Now for some technical stuff.

One of the things I had to do was reverse the direction of this motor because it spins the wrong way for my car. The most immediate question is: "Why don't you just reverse the polarity to the motor?" The answer is because a series wound motor will spin the same direction no matter what polarity you give it.

This is because when you reverse the polarity to the motor, it changes the direction of magnetism in the armature. But because it is series wound, it also reverses the direction of magnetism in the field at the same time. The result is a motor that still spins in the same direction. A series wound brushed motor runs fine on AC (alternating current) as well. Many small household appliances and power tools use them. (In case you care).

This means that to change the direction of this motor, we have to change the polarity of either the armature or field, and not the other. What I did to accomplish this was change the wiring inside the motor to reverse the polarity of the armature only.

I had to un-solder and re-solder the cable on one power post:
And bend one field power connector to hook it up to a different brush:
Now for brush timing. Brush timing is very important. As each commutator bar passes under a brush and current starts to flow into the armature at two points opposite each other, this must be timed perfectly so that maximum magnetic force against the nearby field shoes takes place. You would think that brush timing would be the same for every motor, but it is not. This motor has advanced timing, meaning that the brush is advanced when you compare it to the field pole, as you can see in this picture:
The long line is the field pole center line. It lines up with the field pole fasteners that are further down the motor body. You can see that the brush holder lines up with the "F" marks. I measured this timing to be 11-1/2 degrees advanced, which is about the max for brush timing. If I tried to run this motor without changing the timing, it would turn very slowly and the brushes and commutator would destroy themselves quickly. For the motor to have the same timing in the reversed direction, the brush holder will have to line up with the "R" marks:
I drilled new holes in the end plate where the brush holder fastens to and it now looks like this:
You can see the extra holes in the end cap where the brush holder used to bolt to:
Why have advanced brush timing at all? Many DC motors have neutral timing and work fine in either direction. However, for reasons that are far beyond me, as you increase the voltage and speed in a motor (typically beyond what it was designed for), you need to advance the timing. It is sort of like a gasoline engine that needs more ignition timing as RPM increases. If you do not advance the timing in a DC motor, harmful arcing will occur between the brushes and commutator as voltage and speed is increased and quickly destroy the brushes.

After I got it all back together, I hooked up 12 volts to it to test it out:
It spins the right way! And it seems to spin at a good speed when compared to before I modified it, so it looks like I got the brush timing right.

Saturday, August 3, 2013

Motor Update

On Friday my new (to me) motor arrived. Right away I was able to start messing around with it. Here it is being powered up on the bench with 12 volts:

It spins much much faster than my sepex motor does unloaded, but series wound motors do that because of built in field weakening (something most DIY EVers take for granted!). And it spins backwards. Since it only has two power studs, this will require rewiring some of the internals to reverse the polarity between the armature and field.

Another concern is the tiny internal splines on the drive end. Check out how tiny they are:
The mating shaft is about 1/2" diameter at its smallest point. According to all my research, 50 ft/lbs of torque requires a shaft diameter of 0.55", so this would be iffy at best. One option here will be to bring the armature to my friend Matt (who is a machinist) so he can add a shaft on the end. This would be stronger and less difficult to adapt to my transmission input shaft.

Today I completely disassembled the motor:
After washing all the guk off the bits, this motor looks like it is in very good condition.

Here are the stator windings and armature:
Here are the stator windings and shoes installed in the case:
Here is the brush holder:
And here is what happened when I found some Cat yellow paint laying around:
I wish I would have done all this with my original motor instead of rushing to get the car on the road. It is making me appreciate what all goes on inside of these motors!