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.

Sources:

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…

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One response to “Science Fair season- building stuff, vehicles with electric motors

  1. Pingback: Science Fair season- building stuff, vehicles with electric motors | Gearfire.com

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