Know of a good source for inexpensive gears, pulleys, axles, etc.?

[tastewar]

My son, age 10, is interested in robotics and remote control vehicles, etc, and bought 3 small toy/hobby motors. But of course there's not too much you can do with just motors. And they spin impractically fast to use directly. Does anyone have a good suggestion for where I might source something like a big bag of assorted gears, pulleys, axles, etc. I've seen a few at robotics sites, but they're like $20 for maybe 15-30 pieces. I'm undoubtedly naive, but I know this stuff could be inexpensive. I don't mind if it has to ship from the far east, but my personal attempts to find anything like this on eBay have been frustrating. Any good pointers appreciated...

[adafruit_support_bill]

Old printers are a good source of free motors, gears, pulleys and other mechanical components. Check your local recycling center.

You may also want to look into servo motors: https://www.adafruit.com/index.php?main ... ch&q=servo These are easy to control and have self-contained gear-trains to slow them down to usable speeds.

Continuous rotation servos are great for making robot drives. Standard servos are good for driving arms, grabbers, sensor turrets etc.

[tastewar]

Thanks for the suggestion! Still hoping someone might know of something more directly related, but that might be the better choice in the long run. I just think it would be fun and good learning to have a whole bag o' gears 'n' stuff

[pburgess]

Tamiya (Japanese model company) makes some DC motor gearboxes.

There are some great bits of LEGO Technic as well that are ideal for young folks' projects! If you're fortunate enough to live near one of the LEGO retail stores, last time I was there they had some Technic grab bags that were worth their weight in gold.

[tastewar]

Thanks, that's a good thought...

[chuckz]

My son, age 10, is interested in robotics and remote control vehicles, etc, and bought 3 small toy/hobby motors. But of course there's not too much you can do with just motors. And they spin impractically fast to use directly

I would suggest a lower voltage and maybe using digital potentiometers to control the voltage. Remote control cars have a way to go from slow to fast and I remember having old books that explained radio control circuits. Even if you turned the voltage off and on using PWM or some other way using a microcontroller, I think you could control the speed and turning.

Harbor Freight is a good place for wheels and axels but they are going to be on the larger size.

I think you want to find a truck or toy that you can hack from either E-bay, a thrift store or yard sales.

[tastewar]

Thanks, Chuck. Will definitely play around with voltage and pots. I did find a better search string on eBay. Searching for "plastic gear" (no quotes) in either Toys & Hobbies or Business & Industrial found some reasonable choices. I think I have put together a reasonably good selection, but now I need a gearbox. I know I saw *just the thing* while searching for gears -- a simple U shaped piece of metal with holes for axles. Looked like it could hold a variety of gears. But I've lost it.

[chuckz]

I found this dual gearbox with motors on Sparkfun.

https://www.sparkfun.com/products/319

Seeedstudio also has a 2WD platform for robotics:

http://www.seeedstudio.com/depot/2wd-ar ... ?cPath=170

I would suggest going to arduino.cc and click on "BUY" which brings up a list of stores from around the world. Arduino sites have some of the best prices on equipment because they are catering to students.

I also found this thread which mentions many different companies:

http://ask.slashdot.org/story/08/10/22/ ... -sculpture

I would even see if you could buy an old erector set off of ebay but today they are very very expensive. I'm guessing you can add electronics and servos to erector sets.

But if your school has a metal shop, it is very possible that you could ask the teacher for some help and you could build things very cheaply. There are also citizens with metal shops in their basements but I don't know how you would find them without asking around. There might be some hacker spaces with some powertools that might give you a hand. One of my friend says he asks on Facebook and he usually gets an answer within 24 hours if he doesn't know something.

[adafruit_support_mike]

Gears (and drive components in general) tend to fall in three categories: "not worth it", "not cheap", and "ohmigod.."

The ones at the bottom of the barrel are injection-molded plastic that probably have the right number of teeth, most of which fall within +/-.005" of the specified pitch. I'm sure there are places that sell them, but I don't bother to learn who they are. If you're willing to accept precision that low, there are other options that are even cheaper and more DIY friendly (more on that below).

Even mid-quality gears will cost a fair amount because there are three ways to make them: die-stamping, cutting them one tooth at a time on a mill, or using a specialized gear-cutting mill. All three methods produce good gears, but if you don't pay for "it takes a while to make these," you pay for "you can't justify buying the machines to do this for yourself." You can get stuff at this level from McMaster-Carr ( http://www.mcmaster.com/ ) or Amazon Supply ( http://www.amazonsupply.com ).

The W.M.Berg company ( http://wmberg.com/ ) is a long-established vendor, but they don't have Amazon or McMaster's online presence, and their product is high-midrange and up. There you pay for good materials, good machinery, and the skills of people who make their living making precision gears.

Thing is, you only *need* to use gears for one reason: to get a precise ratio between the number of rotations in and the number of rotations out. You can do everything else gears can do -- stepping up, stepping down, even transmitting very high amounts of torque -- with pressure wheels or belts-and-pulleys. The single difference is that the smooth-surface drive components slip, but gears don't.

Pressure wheels are easy: take two circles of material, run shafts down the center of both, and shove them together. You can think of them as gears with zero (or several thousand) teeth per inch. Wood is a really good pressure wheel material because it's slightly flexible and has good surface friction under pressure. The ideal pressure at the contact point is about 150psi, which scales down to about a pound of seating force between two small circles 1/8" thick.

To make a pulley, cut a V-shaped notch in the edge of your wheel. You can make belts out of string, wire, or O-rings from the hardware store. If you want more grip and less slip, you can wrap the belt all the way around the smaller wheel. You get more wear on the belt, but for cheap-and-quick prototyping that usually isn't a problem.

For materials, you can do a lot with wire. Mild steel welding rod is cheap in 1/16", 3/32", and 1/8" diameters, and makes good shafting. Mild steel MIG wire in .023 and .030 is a surprisingly good structural material at the "less than two inches" scale. It also makes good springs. A 2-3 turn coil of 16- to 18-gauge copper wire around a steel shaft makes a journal bearing. Throw in a drop of oil and a pinch of graphite and it will be on a par with industrial grade bearings. Don't use steel wire journals for steel wire shafts though.. rubbing similar metals together creates rough spots which quickly grind the bearing to powder. Copper wears faster than steel, so the shaft polishes (technically, 'burnishes') the journal.

For wheel stock, check your yellow pages for a local plastics distributor. Where I'm from, polyacetal rod (trade name Delrin) costs less than a dollar per foot in diameters up to about an inch. It's moderately hard and machines well. I'd personally suggest against using acrylic (trade name Plexiglass, Perspex, etc) because it's hellishly brittle and has a low melting point. If it doesn't chip like glass, it wads up like chewing gum. Nylon has properties similar to polyacetal, but costs about four times as much.

One disadvantage of using polyacetal for pressure wheels is that it has a low coefficient of surface friction.. nearly as low as Teflon (don't try to buy Teflon BTW - the prices have gotten ridiculous over the past year or so). You can solve that by roughing the contact surfaces up with sandpaper though. A hole through polyacetal is another good journal bearing.

The other disadvantage of using polyacetal is that it doesn't bond chemically to much of anything, making it hard to glue. It drills and taps beautifully though, so get a 7/64" drill bit and a 6-32 tap for mechanical connections.

You can cast wheels directly onto shafts with polyester resin from the auto supplies section at Walmart. Polyester is closer to acrylic than to polyacetal mechanically, but isn't as obnoxious as acrylic. It has a higher coefficient of surface friction than polyacetal though, so it makes better pressure wheels. Make your molds out of plaster of paris and spray them with PAM cooking oil before pouring in the plastic.

You can also mix dry plaster of paris into polyester resin as a filler, up to where the mix has the consistency of clay. At that point you can sculpt it rather than casting it. It's okay for low-force applications, but if you need something stronger combine it with a wire armature and/or sheets of window screen for large surfaces.

Ideally you want two wires/screens to handle the force, with the plastic between them. When something bends, the convex surface stretches and the concave surface compresses. You want your metal close to the surface where it can resist those forces. The plastic just keeps the chunks of metal in the same position relative to each other, effectively making them a single, thick beam.

[chuckz]

Old printers are a good source of free motors, gears, pulleys and other mechanical components. Check your local recycling center.

I read that page scanners and office copiers have gears in them. Gloves are a must to keep from getting hurt by tearing these machines apart.

[chuckz]

I googled 'copier gears' and came up with all sorts of gears costing from .70 to $26 dollars. I found copier gears on ebay but I wasn't satisfied with their prices.

Deal Extreme also had a car chassis with four motors for $26.

[tastewar]

Whoa, mstone, that was quite a lot of info! Guess I am not nearly as resourceful as you. I'm sticking with the "cheap/not worth it" level for now. If the boy shows a lot of interest, we'll move up in quality, but at the moment, I'm just looking for something that he can play with to see some of the principles in action.

[adafruit_support_mike]

Whoa, mstone, that was quite a lot of info! Guess I am not nearly as resourceful as you.

I've just spent more time pounding my head against this particular wall.

I'm sticking with the "cheap/not worth it" level for now.

Makes perfect sense. The good news is that the "just poking around" level is very DIY friendly. You don't have to worry about precise measurements, good centering, etc. Dowels, wire, foamcore pulleys and rubber band belts are good enough for basic make-it-move stuff. If your axle is 1/4" off-center, it just means the speed will be a bit uneven.