Monthly Archives: March 2008

Where To Get Small Electric Motors, San Francisco Bay Area, for science-fair projects, etc.

Partial lineup, Mabuchi Motors

Some, but not all, of the motors Mabuchi make today. From 5 people 50 years ago to 40,000 today….

So I now have some data to back-up my speculations:

Mabuchi Motor Co. US Product catalog

1) Aristo-craft pack a line of Mabuchi or Mabuchi-like electric motors, sizes 130, 140, 260 and 280, which have a retail price for $2.85 to $3.95, depending on size and whom you buy it from. They’re a great deal because they each come with a little stamped steel mount that holds the motor and which you can use to attach it to your project. Better than rubber bands or hot-melt-glue. You can take them off and use rubber bands or hot melt glue if you want.

They also come with 3 plastic gears to fit on the common 0.079″ (2mm) motor shaft, making it easier to connect the motor to something. Other gears, or push a sewing machine bobbin over the gear or hot-melt-glue something (K’nex, Lego) to the gear… They’re in a little clamshell blister-box with a yellow sheet of paper giving the model number on the front and the specifications for the whole range on the back. The packs are about 3″ X 3″ (aka 75mm square).

All four sizes, the small ones for 1.5V typically, the larger ones for 3V, typically, are available at Hobbies Unlimited in San Lorenzo and J & M Hobby House in San Carlos. I’ll report on what other stores stock them as I know it. $2.85 or $3.35 for a 130 size motor with a mount and three gears is a pretty good deal, considering the purchasing power of $3. The 130 runs willingly on a single AAA cell

1a) There seems to be a Japanese-originated standard for small electric motors. I’ve seen 130s to 540s and many sizes in between. I’m not sure if its a measure of optimum energy output, length * diameter in mm or what.

2) There are larger motors in the same series, up at about $9 and then there’s another price point around $12. Dumas packs motors in the $9-12 range for battery powered model boats. After that you’re looking at the standard RC Car motors, from $15 to the sky’s the limit. MAJOR power, drawing on MAJOR batteries! If you want more, or more efficiency, look at the “Speed 400” and “Speed 280”, which are based on standard electric motors from rechargable battery powered tools. A “Speed 280″ is about the same size as the 280 that Aristo Craft packs for $3.75-3.95 retail, but costs more, and can both draw and produce more power. Beyond that, you’re into the brushless motors used by electric model airplanes- much more efficient than DC brush motors, for the same battery power. But you’ll need a controller. Figure $25-50 for something that works, before you buy the battery. You’re paying for the low wieght and high efficiency.

For that kind of money you could buy a rechargable tool AND battery and perhaps a spare battery and use it for motive power in your project. And you’d have the tool to remember it buy when you’re done. Almost any electric tool will have a robust reduction gear set along with an on/off switch, possibly variable speed, possibly reversing. In their last year, the Odessey Of The Mind team that I coached used two rechargable drills to power a one-person vehicle that drove around on patios, quiet streets, and high school gyms. 3/8″ steel axles were chucked to the drills and very small tires and wheels fastened to them as well. The wieght of the vehicle was carried on some kind of bearing the axle ran through on both sides of the wheel- copper tubing fitted snugly into a block of wood might have been the bearing- I didn’t invent it! The drills ‘floated’, other than being restrained from turning in reaction to the torque they applied to the wheels. They were mounted upside down and the tires and wheels used were a compromise between what would let the drill run at its optimum speed (about 1/4″) and what would allow the drill to clear the ground! (about 3/4”)

3) I’m pleased to report that Radio Shack also sell electric motors, with several available in the 1.5-3.0V range and for a $4 or a bit lower price. My local Radio Shack had a ‘260-like’ motor, 250mA, 3.0V, for $3-something, a smaller, higher voltage motor that came with a metal gear, and some larger motors at the higher price points.

4) Of course, you can also shop on the Internet, starting by searching for Mabuchi in titles AND descriptions of all items at eBay. You’ll find everything from 540 series motors used in stock RC cars by companies like Tamiya, to people selling the little tiny motors used for pager and cell phone vibrators. You can get the $1 motor this way, but you’ll pay shipping.

5) If you’re willing to pay shipping, Did You Know that K’nex has a catalog and will sell loose pieces? Like gears, wheels and tires. Wheels and tires are opportunities to scrounge and invent but gears are more hassle when you’re inventing. Its never bad to know where they can be bought. They’re made to turn on or lock to K’nex “sticks” and that can be readily attached to other things.

6) Radio Shack sells battery holders for 1, 2, 4 and 8 AA cells, 1 and 2 C or D cells, closed boxes with lids as well as open holders. Single-cell AA holder is $0.99, the simplist versions of the larger ones are $1.99 or less. Before you say “Battery holders are for wimps, I’ll just tape some telephone wire to the button and bottom of my battery cells”, consider how easy it will be to change to fresh cells, or swap rechargable cells, with a first-class regulation battery holder. You could even have someone else do it for you!

7) Just like with restaurants, its worth your time to find out what’s local where you live, or where you are, and patronize them. Hence my leading with Hobbys Unlimited and J & M Hobby House. Try the yellow pages for your ocal electronics parts and/or surplus place when looking for switches, battery holders, etc.

8) Extra Credit: If you put an incandesant flashlight bulb in series between your battery and your motor (3V or more, with appropriate bulb…) it will light up in proportion to the current flowing through the motor- lots of current, lots of light. Little current, not much light. Spinning freely with no load, the motor won’t light the lamp very much. Put some drag on the motor and watch the light get brighter. Its brightest when you’ve completely stopped the motor. You can use this interesting behavior to show when your motor is being loaded and when its spinning freely… Can you apply that to your project?

9) Extra extra credit: Make your own motor!
Michael Faraday invented the homopolar electric motor, taking advantage of the magnetic field from a current running at 90 degrees to the direction of electron flow…

Wendell Oskay's take on Faraday's Homopolar motor

Windell Oskay’s homopolar electric motor, made from a drywall screw, powerful rare earth magnet, single “C” cell and a 6″/15cm piece of copper wire.
wire loop motor
There is a trick, and the trick is, not all the insulation has been removed from the two straight bits of the wire that stick out through the safety pins. When connection is made, an electric field is created and that change in the electrical field creates a magnetic field which attracts or repels the button magnet on the wooden base. The loop turns, the connection is broken, more change in electrical current, more magnetic field. The momentum of the mass of the wire carries it on until it connects again and the whole business starts again. Extra points for figuring out how to get it to do useful work, more for finding the optimum amount of wire that should be bare and that which should be stripped, and the angular relationship between the stripped area and the coil…

Science Fair season- building stuff, vehicles with electric motors

I see kids and parents walking around some of my hangouts with folded papers in their hands looking for stuff to build science fair projects. Many times, electric motors, small wheeled vehicles and that sort of thing are being sought. Here’s a couple of quick words of advice and I’ll do more reesarch on what’s available where:

1) Electric motors for battery powered things: 1.5 to 6, 9 or 12V DC motors. Smallish unless otherwise indicated. The “Mabuchi” motors of my childhood, no doubt made in China now. The higher voltage ratings will work slower with smaller voltages from small numbers of batteries, but 1.5 or 3.0 V will make a 12V motor turn, possibly at more or less the speed actually needed.

Generally, electric motors are too fast for the wheels, propellers or other mechanisms that they propel things through. So some gear reduction is in order. If you salvage your motor from something, it may come with the reduction hardware- usually a small gear on the motor and a larger gear for whatever the motor is turning- wheel axle, propeller, treads, fans, etc. The secret is that the motor turns something small and that small thing turns something big- this reduces the speed and increases the torque by the ratio of the small thing to large- count the teeth if gears, measure the diameters if pullys.

A convenient “belt reduction” you can build from stuff found around the home can be made by putting a bobbin or some other small, flagned, pulley, on the motor shaft, and a thread spool or other large, flanged, pulley substitute, on the axle you want to drive. A big, fat, rubber band transmits the power. Thread spools can be sawn in half and the halves glued over an axle, with hot melt glue, if the axle is already installed. Obviously, one can cut down a spool width as easily as cut it in half. Using an idler axle between the motor and the load you can have a Two Stage reduction too.

Gear reductions and gear sets based on Lego gears, K’nex gears or various gears available to experiementers are also possible. For toy-sized projects, Lego gears are good choices, but not for something you want to ride on yourself!

Rubber bands can be shortened and sewn together. Rubber strip for flying model airplanes and lightwieght bungee cord are available if long loops are desired.

Various sizes of pre-made wooden wheels and spools are available, as well as the lovely but expensive RC Car tires and wheels, RC Airplane tires and wheels, etc. Scale model car tires and wheels are usually better to look at than use- the tires are too hard. Inexpensive wooden wheels with a rubberband stretched around the outside have much better traction. If you need cheap, consider tuna or cat-food cans with a rubber band or two stretched around them. Metal or plastic pipe caps make dandy wheels, as to slices of dowel. A slice of the dowels used for hangers in closets, with a length of bicyle inner tube over it, makes a very usable, very inexpensive, wheel.

Axles: Steel is good, especially with brass tubing for bearings. Brass or copper rod or tubing is ok, Wooden sticks, dowels, bamboo skewers and other round things are good. Use brass or plastic tubes for bearings. Even plastic rods or tubing. Plastic straws make all kinds of structual stuff, if light-wieght is a goal. Carbon fiber is fun if you know how to cut and shape it and don’t care that much about cost. VERY stiff.
Bearings: A hole drilled through the structure is always a good start. Brass tubing or copper tubing or plastic tubing can be oiled or greased, after its attached. Its generally a good idea to use the axle or a dummy axle to hold the alignment of sets of bearings when attaching them to a structure. Depending on what you’re doing, you might even allow a screw adjustment for alignment.

A hole through something hard, hardwood, a block of metal, a thread spool, can serve as a bearing. Aluminum is soft but works great for flying airplanes- steel shafts through aluminum brackets, with beads or small brass washers, for thrust bearings, are popular with rubber band airplane enthusiasts.

If your motor or bobbin or axle or thread spool doesn’t fit and there’s too much space, use nested brass or plastic tubing (or rubber tubing…) to fill the distance without loosing the ‘center’. The advantage of rubber band belts and rubber tubing to make sizes match is that it allows a little lee-way in alignment. If you build with gears, you have to get your holes in the right spots and aligned correctly. Gears are pretty unforgiving of misalignment.


Radio Shack sometimes stocks 1.5-3 or 6V motors.
Target has some toy car product which has removable motors and is selling a pack of replacement motors right now.
This is right up Hobby Engineering’s aisle, give them a call. You can have dim sum at the nearby big, fancy, chinese restaurant..
Some hobby shops (D&J and Berkeley Ace Hardware for sure, likely Hobbytown) sell science-fair experiementers supplies, including motors.
Some (D&J again, and Fry’s Electronics) have Tamiya’s line of inventor stuff, including motors, gear boxes (fixed ratio and selectable), crawler treads and the like.

Most hobby shops and many hardware stores have brass tubing, and most successessive sizes of the small stuff (1/16 inch to about 1/4 inch) ‘nest’, like an old telescope. Plastic tubing that nests is also available, and because its made from oil, may cost more than brass! Use aluminum tubing if you need something really soft, but still stiff. Use steel tubing if you need something strong- stainless steel won’t rust, a convenient property. If you want to attach axles, gears, pulleys, etc, to an axle, consider simply drilling a hole through it and sewing a piece of wire through the hole. You can be fancy and use a cotter pin if you want. Filing one or more flat spots in the round axle is another good technique, if you can get something stiff up against them.

I’ll do some more research and post what’s available here. I still remember coaching a terrific Odessey Of The Mind team back in the 1990s, and I haven’t lost my enthusiasm for the subject.

A good $2 investment is a battery holder from Radio Shack, etc, that holds the cell(s) you want to use but allows you to replace them. Really slick stuff compared to using masking tape to hold a bit of telephone wire to the end of one or more cells…

One-handle temperature and volume control faucets. hours-of-darkness plumbing repairs :^)

So my sweetest Jean calls me at work and says that the kitchen sink started spraying water everywhere and when she got Benjamin’s attention, he turned off the taps under the sink while she held the handle and mixing valve assembly in place… and this situation will prevent the dishes from being washed, because the dishwasher is on the same taps… should they do the dinner dishes in the bathtub?

Along with “going to work” and “paying taxes”, you can add “hours-of-darkness plumbing repairs” to the real list of “Adult Subjects”! No, I’ve never seen this stuff in any movie or book either…

Now we’ve been around this bend a couple times already- there’s a disconcerting ‘loseness’ in the handle and then the whole business comes off in your hand and water from the supply pipes is shooting up and bouncing off the valve. There’s a retaining collar that holds the valve down on top of the common gasket for hot and cold in, and the path out to the spout. When the collar backs itself out, it, the valve and the handle are free… and you have to disassemble the combination before you can put it back where it belongs.

Fortunately, it was a weekend and daylight the first time this happened. By trying every other possible tool, I determined that the grub screw holding the handle to the valve is a Torx #10, and took it apart. A low-quality stamped steel ‘wrench’ purchased for large plumbing threaded stuff can sorta get a grip on the retainer’s flats, helped by a dishtowel to protect the pretty, chromed, brass retainer that can’t really be seen once its all togther. I go to finger-tight with my fingers first- really oughta buy a wide, wide, spanner set or adjustable wrench. My beloved brother Ian, a far more accomplished constructor, mechanic and fix-it guy than I, calls the Crescent style adjustable wrench, “The wrong tool for every job”. And he carries ’em in his tool boxes just like I do… but I digress.


I had a feeling that the valve and its faucet would require more maintenance after the first time it came apart, if for no other reason than the thick, heavy, rubber seals for in and out flows in the valve body are far from pristine looking… but nothing blocked the flow too bad, and the sink would be ‘down’ if I took the valve off to the hardware store for new seals… so I never did. This kind of procrastination seldom actually fixes anything, or prevents the wear and tear of the physical world, and so it was in this case. I’d probably enjoyed taking it apart and putting it back together 2 or 3 times before this latest one.

But this time was different. Sure enough, the retainer had backed out and I found the Torx set and started working on it, but I noticed that the handle didn’t move as freely as I was used to… and sure enough, when it was all apart, no question, the valve was binding when the handle rotated or moved fore and aft to open or close the common flow passage… and that’s how it was coming undone- with a little binding, torque exerted to move the valve was finding its way to the retainer, and unscrewing it.

Ok, that explains that, now what? The valve is a clear-plastic gizmo with three rubber-bushing-sealed holes in the bottom, and a set of bumps and indendations that prevent it from rotating against the common gasket in the spout column. The outer casing is more than one piece of clear plastic, glued together, with a pair of ceramic plates, the lower one fixed in place, with two input and one output hole through it. The upper plate moves, and has indentations, but not holes through it. Lining up the indentations in the top over the holes in the bottom allows water to flow. The two ceramic surfaces are so flat and perfectly fitted to each other that they prevent water flowing unless an indentation is over a hole, but can slide back and forth.

Ours, however, weren’t sliding, and it was easy to see why. Some black or dark gray plastic piece that had been in the top of the cartridge was wearing out and its remains were stuck in the space at the top that the lever moved in. Black stuff had also built-up in on the ceramic sealing surfaces, so operating the valve with the handle was difficult, and just about impossible without the handle for mechanical advantage.

To make a long story short, this valve “cartridge” follows the (loose) conventions for “European” 40mm single-handle faucet cartridges- it is, for example, 40mm in diameter. There are a number of different cartridges and cartridge parts for sale in Berkeley and Oakland, at Ace Hardware stores, Orchard Supply, etc, but I haven’t found any American Standard 40mm “European” style replacements yet. Have to look harder, try the internet I suppose.

So here it is, midnight, and I’ve got this thing in my hand and the sink doesn’t work. Two choices- put it all back together as is, not functional, and turn on the water so the dishwasher can run, or try to fix it here late in the night. Of course I opted to try to fix it.

There’s a pair of bosses that the lever passes through and a roll pin serves to keep it all in place and provide a pivot. I drove the pin out with a bamboo teriyaki skewer, and had more loose pieces, but wasn’t any closer to the guts where the trouble was. It was time to apply wisdom others have taught me.

My friend Ted Brattstrom is a great tinkerer and taker-apart of old stuff. Long ago he taught me that if you find something that’s not working, and looks dirty or in need of cleaning, taking the thing apart and cleaning it gently but thoroughly, then re-assemble it. In better than half the cases, the item will work when re-assembled. Maybe not well, maybe you’ll know its got only a bit more useful life, maybe you’ll know to be VERY gentle with it, but it will work. But I couldn’t get inside the clear plastic bit to clean out scraps of plastic junk that was getting in the way, nor could I figure out how, precisely, the valve worked. Eventually I concluded there was no alternative to cleaning it as best possible as it was, and trying to understand it, and perhaps if that worked, the faucet would work too.

So I filled the open spaces and my palms with liquid soap and started trying to separate all the crud off the good pieces and float it out. I poked with my bamboo skewer. I flipped it over and saw all the black plastic bits that had built up on the ceramic surfaces, and scraped them with the bamboo. Between soap, scraping and flush-outs at the bathroom sink, I got the sliding surfaces clean and most of the junk out of the top. A little work with tweezers and long nosed pliers got the rest. Now the valve was clean, moved as freely as it ever had, and I was confident I’d missed not possible way of takingit apart. I put the biggest piece of removed plastic back on a ‘nose’ sticking out from the upper, moving, ceramic piece, which was guided by the plastic ‘glove’ over this protuberance. I had to trim off some damaged pieces, and rinsedin the hottest water I could stand, put it all back together, and at about 2:30 started the dishwasher, secure that we could run the sink next morning.

A few days later if failed again, and the remains of the little plastic bit that guides the upper ceramic plate were now gone. Without the plastic’s guidence, the plate can rotate and the ‘nose’ can get entangled with other stuff inside the cartridge.

I sorted through all my considerable stash of plastic bits and pieces, but coulnd’t find anyhing right enough to replace what had worn out. Then it occured to me make something not exactly like the old part, but formed of bent styrene and capable of cushioning the parts without binding them, and guiding them gently. Alas, there wasn’t space for the pieces of plastic I had.

Then the penny dropped and I thought- Oh Yeah! I got a srip of brass the same width but thinner than the plastic I was using- .5mm or less, vs .75 or more for the plastic. It took two tries to bend a suitably shaped sheet-brass replacement bit, and it works great.

I still need a new cartidge, but I’ve brought this one back form the dead 3 or maybe 4 times now.

A real relic of the cold war, a Yugoslavian map of the northern New World…

showing the Mexicans attacking Texas, the separatist Black Muslims encamped around Chicago and the Quebecers fometing revolution…. as well as (apparently) the North Slope oil pipeline, and more obscure things as well. A real blast from the past.

L7’s “Hungry For Stink” is a grinding, roaring, sweaty, smelly, joy!

I couldn’t help myself, I had to write a review of L7’s “Hungry For Stink” after reading a dismissive review of it on a CD site…

Although it did not equal the commercial success of “Bricks Are Heavy”, “Hungry For Stink” is many fan’s favorite, both of L7 and for the the Grunge era. The music, lyrics, production and feel are dark and heavy, but a bright, manic, defiant, optimism shines through the whole record, not unlike that in the Ramones’ classics, “Road To Ruin” and “Rocket To Russia”. Although recorded very nicely in a studio, the sound is that of a working band that’s tight, in practice and has some great, new, songs they’ve worked out on stage and want to capture. No studio experiments, and nothing self concious or half-serious about it.
“Hungry…” erupts with the anthemic “Andres”, a song about “a guy with long hair” who can fix the air conditioning… the heavy groove proves in every sweet, thundering, bar, that ovaries don’t get in the way of playing rock and roll. And never did.

The 11 songs that follow range from the punk dirges “Baggage” and “Talk Box” to the sharp, alienated rock of “Can I Run” and “Freak Magnet”; the hard, power-pop sensability of “Riding With A Movie Star”, “Stuck Here Again”, and “She Has Eyes” and more mosh-pit screamers like “The Bomb”, “Shirley”, and “Fuel My Fire”.

A little bit of rock-star introspecton, grunge-style, slips in with “Questioning My Sanity”

“Shirley” is about drag-racer Shirley Muldowney, including hilarious, seamlessly integrated, samples from her bio-pic “Heart Like A Wheel”.

Song writing and lead-vocals are shared by all four band members, which only adds to the grace and polish of the performance. Rough, abrasive, aggressive and like it is, straight from the shoulder, for sure. But its not just attitude and genius; in the day, L7 had the chops AND the brains to take every opportunity, and apparently had a great time doing it. And you can still share that grinding, roaring, joy.

*About that optimistic light- except, perhaps, “Talkbox”, which is a very effective slice of a bad dream. Great, but strong stuff.