The BFM-9000 Motor Mod (tm) (pics)

[actofgod]

I had a crazy idea a while back.

While ordering the button cells for the Layman's mod, I picked up a couple of Small DC Motors from Allelectronics. These are much larger than the bit motor, but smaller than your average hobby dc motor. From the dimensions listed on the web page, I thought I could possibly fit one in a bit. Thus was born the BFM-9000 project (incidentally, named after Doom's Big Friggin' Gun).

I had in mind a high-torque monster bit from the beginning. The motor is rated at 15800 RPM at 2.4v 96ma, so I knew that even with dual cell it wouldn't be super-fast. I decided to push it a little and give it 3.6v though, and I chose a variation of the Layman's button cell mod using 3 80mah button cells. This would overcome the current-providing limitations of the smaller cells and allow better run times, but naturally would not fit in the same space without modification. Shown in the first three pics is a size comparison between a bit motor on the right, a clone motor on the left (the "large" type that will barely fit in a bit motor mount), and the BFM-9000 in the middle. Also, you can see a strip of the three button cell batteries I used, shown next to a stock bit batt.

edit: oops, the batteries are 80mAh, not 70.

[actofgod]

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[actofgod]

The next step was getting the three batteries and the motor crammed into a bit chassis. I trimmed down the battery compartment area and cut through the sides completely, leaving only two small vertical strips of plastic from what used to be the side walls to hold in the batteries. I removed the wall separating the battery compartment from the motor compartment, being careful to leave enough plastic connecting it to maintain structural integrity. I then dremeled down the side walls of the motor mount compartment until the huge dc motor would fit. I originally planned to leave one of the walls intact, but because of the size of the motor I had to take out both. It barely fits as it is. I left enough plastic at the bottom of it to keep the back end (with the tab) attached to the rest of the car, and superglued the motor to the remaining plastic in the motor mount compartment. I flipped the PCB and rewired everything. Here are some pics of the batteries and motor installed.

[actofgod]

What good is all that power without some good tires? I first gave it a full-size wheel mod, then took some wheels from a Muscle Machines car kit and sanded down the plastic treads with a fine, cylindrical dremel bit until the tires were smooth, letting the wheels spin freely between my fingers and using minimal pressure to keep them nice and round. They actually turned out to be more perfectly round than before I started. They were smoother and softer than before, but still didn't have as much traction as the stock rubber bit tires, so I added a very light coat of rubber cement and let it dry, which is an idea I read elsewhere in this forum to improve traction. It helped a lot, and seems fairly durable so far. I may have to reapply it eventually. The wide surface area of the tires also helps.

With the hub caps included in the car kit inserted into the tires, there is just enough room to fit a bit rear wheel into the other side. For now, I have left them removable, but eventually I will probably center them perfectly and superglue them, because they can wobble or come off if the car hits something. See the pic below for a better idea of the way the wheels attach. After test-driving, I added a second steering spring to help swing those big guys back into place and noticed sharper steering immediately. The electromagnets have no problem overcoming the extra spring, since they are getting triple voltage now anyway.

[actofgod]

Matching up the gears was the hardest part. A pinion gear is a tiny bit too small (though I did manage to fit one on for testing), and a transfer gear is a tiny bit too large, but I put a tiny drop of superglue on the motor rod and slid a transfer gear over it, spinning it a few times to evenly spread the glue. It was such a close fit to begin with that it turned out perfectly centered. However, I was disappointed with the performance until I readjusted the motor position to reduce gear friction and binding, which almost doubled performance. I had to fine-tune the way the gears mesh before getting just the right position, and anyone else wanting to do something like this may have a different position depending on how much plastic you've dremeled away. The first pic here shows the gears more closely, though I've changed positions slightly since then. I used the light blue high-torque gearset for faster acceleration and more climbing power. I'd say the speed is roughly equivalent to a 2.6-3.0 (not too shabby) but it has amazing climbing power. I don't have a video camera, but it will jump the metal divider between my kitchen tile and living room carpet and keep going full speed on the carpet. I haven't tested the highest slope it will climb yet, but just judging from how hard it is to stop the tires with my fingers I can tell it is going to be pretty impressive, probably limited more by the tire traction than by the motor. I may get a Wild Char-G sometime and compare them. It may also be fun to repeat this mod on one of those.

[actofgod]

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[Heat]

wus rubber cement? i wanna put that on my tires too now that you made it sound so good.

[actofgod]

When resoldering the PCB wires, I used some fairly stiff wire, and it pretty much holds the PCB in place. I might add a thin rubber band around the chassis and PCB to further secure it if it becomes a problem. The body will need a regular lift mod; it fits just about perfectly when resting on top of the body tabs now. All that remains is to adjust the tabs several millimeters higher and dremel out a little more clearance for the larger wheels. I haven't picked which body I want to use yet, but for the pics I've put a couple different ones on there to show what it will look like when completed.

[actofgod]

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[actofgod]

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[actofgod]

Ok, that's it. Just thought I'd share that crazy idea with everyone; I don't think I've seen any mods using motors bigger than the bit motors, at least not to this extreme. I don't think you could go much larger and still fit the motor between the tires and under a body, but I'd love to see something even wilder.

Happy modding.

[actofgod]

Originally posted by Heat
wus rubber cement? i wanna put that on my tires too now that you made it sound so good.

Refer to this post for more info on Muscle Machines tires and rubber cement. I had already found the tires before I found this post, but it was still helpful.

[xatu]

That is really cool! Does it give more speed and torque?

[actofgod]

Originally posted by actofgod
I'd say the speed is roughly equivalent to a 2.6-3.0 (not too shabby) but it has amazing climbing power.

[xatu]

Ah, never saw that.....