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