The BFM-9000 Motor Mod (tm) (pics)
 

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.

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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.

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.

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.

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

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.

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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.

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.

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

Ah, never saw that.....

yea the rubber cement was my idea... i have been running on those type of wheels for a while now.. the nice thing about it is that if the rubber cement gets funky you can just rub it off and put on a new coat.. kinda like getting a fresh set of rubber.. im liking your mod a lot. great job.. i guess all i have to say about muscle machines is that there are different size wheels. i beleive the cartoon seris has the massive wheels, all of the others pretty much have the same size rear wheel.. you can tell the cartoon by the package, also the cars usually are lifted in the rear of the car with tiny wheels in the front. i used the massive ones on the rear of my car, and the normal on the front.

for moounting the body. I used the antenna hose from my 1/10 rc and cut off a little piece and super glued it to the chassis between the batteries.. (internal dual cell). i put a hole in the top of my beatle body to accomidate this post.. and one screw. i know this wouldnt be the prefered method. im still working on getting a way other than screwing through the body, because i think the screws kinda suck when showing.but i painted mine so its not very noticable... the only other easy way i could think about would be a velcro attachment. but once again i dont like velcro to much. Im looking forward to seeing how you raise the tabs. please post pics when you do. heres a pic of mine...

my next mod is gonig to be simmilar to yours. although im using a slot car, and 4 cells. so i will probablly have to do the laymans mod too.. i have tested out the motor with 4 cells and there is unbelieveable torque, and plenty of speed. fastest ive seen so far. i just need to find someone with a slot car track and a voltmeter, so i can find out how much voltage they get at full throttle...

Ya, great idea on the rubber cement Spanky. Can you tell me anything else about the latex molding compound you mentioned in that post?

Nice idea on the mounting, though the screw does make it a hassle. I haven't decided quite how I'm going to alter the tabs yet. One way would be to cut the old ones off and try supergluing them higher on the body, but I'm not sure if I can get it quite high enough. Another way I'm considering would be to use two pieces of springy metal, fashioned into a sort of "Z" shape. The flat, bottom part would be fastened to the old tab. The flat top part would be trimmed to the same size as a normal tab; to put the body on you'd just push in the two metal pieces slightly and pop the tab part into the slot on the body. I think that would be pretty durable and hopefully easy to change out, but I'll have to measure everything carefully first.

Can you post pics of the slot car motor you're talking about? Do you think it will fit in a bit chassis? What are the specs (voltage, RPM, etc.)? I think my wheel mod is not bad (I've seen several better on this site), but the neatest thing I did with this mod is the huge motor. I'm curious if anyone else has found other non bit-size motors to use in their cars.

ok, heres that slot car. im not sure what the rpm's are but i know that this thing fly's.. like ive said ive only tested it with 4 cells. a 9v would be ideal but keeping the pcb from frying would be hard to do..

the yellow body is for the slot car. and i have two bits by it. i microsizer and one prescious, with a shen s2000 cap(painted windows :mad: )

http://custombitbodys.home.attbi.com...omparasion.jpg

i think a better way of mounting the body would be to attach small tubes like shown in the above pic to both the body and chassis, and then use something like small finishing nails to fit in the hose to hold them together... but i think your idea of the metal Z sounds even better.

the latex im using is a mold maker latex. the kind you would brush on something to make an impression. the should have it at a craft store. rubber cememt would probably work better though.. after 2 runs the latex is coming off the tires..

How big are those batteries compared to a bit?

wtf? My posts are before yours, even though you posted them like a day ago... Weird.

hehehe, i just found myself a BFM.... (big flippin motor) it also came with two 1/2AA 300mah batteries.. i destroyed a electric toothbrush that i found under the sink. im not suer if the batteries are good... im gonna try charging them... but the motor has more torque with 2 batteries than any other motor that i have ever saw. now i just have to get some gears that will work on it... im thinking about using this with the rear axle of the slot car... so that i can put the motor in the middle to front.. and then put one battrey in the front and one in the rear.. that would even out the weight.

btw the motor is just a tad to big to fit inside the chassis right now..

You can sorta see the comparison in one of the pics, but the closest thing I could compare it to is the rear wheel of a bit. The narrow end of the battery is about the same diameter; the flared end is about a millimeter wider. The thickness is about a half millimeter wider than the rear bit wheel. I don't have a ruler handy, so I couldn't tell you the exact dimensions. They're considerably larger than the button cells in the Layman's mod, but they are 80mAh instead of 40mAh.

Actually, I was talking to Spanky to see what size his 1/2 AA batterys were.... But my post got all messed up. :confused:

how big are they? well 2 of them equals 1 AA battery.. so.. thats about how big they are...

Pics Updated
 

I finally got a new digital camera, so I replaced several of the tiny, blurry pics with some higher-res ones. I still cropped and compressed them to save download time though. I hope these will show the details of the mod better. Check them out back on the first page. You may have to hit "Reload" in your browser to get the new ones to show up.

Actofgod-did you get those 70mah buttons at the same site as the 40mah for the layman's? If not could you provide the link. Thanks.

we seriously need a movie
 

i wanna see that big baby in action.

Oops, I just noticed that I've been saying 70mAh when the batteries are actually 80mAh each. Yes, I did get a six-pack of these from the same site as the other button cell battery packs, allelectronics.com, but they no longer list them on their web site.

They are Varta V80H button cells, if you'd like some. It's a pretty common battery. Just doing a quick search on yahoo, I found that mouser.com has them in a handy 3-pack, shrink wrapped and with soldering tabs for $5.66, though I don't know about shipping since I haven't ordered from them before. If you're comfortable doing a standard dual cell mod, you should have no problem with this one either.

As for the video.. I'll see what I can do :)

Hummer Body
 

Finally got an appropriate body for this baby, a Hummer H1 body from a Cannonball clone. It looked ridiculous with the original, tiny tires, but it's pretty sweet now. I'll need to dremel just a little extra wheel clearance in the front, but this one already has much more clearance than most.

Here are a few pics.

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That thing is pretty pimp-tight man :cool:

As much fun as this mod has been, I still want more climbing power. I found a great little 4x4 that I'm going to start tinkering with. Check out my 4x4 dissection pics.