What Kind of Electric Motors Should I Get?
October 23, 2008 11:29 AM   Subscribe

Where should I look to find good, low voltage electric motors for projects?

So, I'm studying electrical/computer engineering and although I'm pretty early in the program (sophomore level classes right now) it's something that I'm really interested in, and I want to be able to experiment on my own. I have an Arduino and have been having fun with that, but one thing I want to add on is the ability to control things in the real world...things that I need motors for.

The problem I've run into is that I don't really know what type of motor would work. I think what I'm mostly concerned about is getting something that will have some torque, and also figuring out how to attach it to something. One specific thing I'd like to do is create a device that can mechanically turn the dial on the air conditioner in my dorm room.

I realize that for the Arduino I can get a "motor shield" add on that will make it a lot easier to attach various types of motors to the Arduino, but I can't figure out what kind of motors to get and where to get them.

So, in summary: What kind of motors should I get for random electronic projects? I feel like torque would be more important to me than speed, but both would be good. And, where can I find these motors?

posted by DMan to Sports, Hobbies, & Recreation (18 answers total) 6 users marked this as a favorite
Best answer: Sparkfun. Specifically the dual-motor gearbox plus some wheels (available lower on the same page). If you're EE/CS you don't want to be wasting your time building a drive train from scratch. "Normal" cheap low-voltage motors (a) are a pain to interface with and mount, and (b) run up into the thousands of RPMs @ low torque and need to be geared down significantly to work. You might find a cheaper supplier but you won't find one as well-tuned to hobbyist/hacker work.

In general, I've used Limor's "Where to get stuff" reference for years to jog my memory.
posted by range at 11:41 AM on October 23, 2008

If your school is anything like mine was they have several IT departments for different departments and groups within the school. And some of them have old printers and copiers lying around waiting for disposal. And printers tend to be chock full of fairly powerful and small electric motors with small gearboxes attached. I'd say go junk mining before you deplete your precious beer and top ramen fund.

P.S. with permission of course
posted by frieze at 11:48 AM on October 23, 2008

The people on Ace of Cakes talked about problems finding these kind of motors for their more elaborate cakes, but finally found one they loved. You could probably email the show and find out what they are using.
posted by mikepop at 12:06 PM on October 23, 2008

Lego motors used to be high efficiency low voltage gear motors. I'm not sure if the current line is as high a quality as I haven't bought any for a while. Lego motors also happen to be compatible with Lego bricks and beams (fancy that!) which can make for fast assembly of a rough proof-of-concept.

Low-energy robotics: Solarbotics
Surplus stores: Sciplus, Electronics Goldmine

busted toy robots, cassette players, wine-bottle openers, cordless drills, etc etc. Anything that has moving parts and is battery powered probably has a motor and geartrain in it. The main trouble will be that much of the time the geartrain will be incorporated into the case, so not removeable as a discrete unit.

You might also be interested in looking into relays, so you can use the ardino to control mains-voltage appliances.
posted by -harlequin- at 12:07 PM on October 23, 2008

Are there any pick-your-own junkyards nearby? Cars have lots of motors and servos in them - power windows, power seats, servos that control duct doors, starter, etc. Most of them should run off 12 VDC, I think.

I would second junk electronics, also.
posted by backseatpilot at 12:38 PM on October 23, 2008

All Electronics
posted by kc8nod at 1:33 PM on October 23, 2008

Jameco has some good 12VDC geared motors for around $15/ea. You could also modify an R/C servo to continuously rotate in either direction.

I don't think a 12,000 RPM hobby motor would be of much use on its own.

Careful with overloading the motor shield... 0.6A continuous per H-bridge isn't much, especially with a loaded gear motor.
posted by lalas at 2:44 PM on October 23, 2008

For general tomfoolery/hacking:

I have huge assortments of motors scrapped from old VCRs and printers. They are not particularly high-torque, but they definitely are easy to drive from Arduino.

Think about it this way -- in a printer, VCR, or CDROM, there are small motors which MUST be controlled by a microcontroller. Therefore, those are the places you should be looking. I get tons and tons of this kind of electronic detritus from the trash and from friends upgrading... you can too.

For specific projects:

I completely agree with Range. I've wasted far too much of my life using subpar stuff when, for a little money, I could have just purchased a much better solution. A lot of my fun projects have died because I lost motivation after fighting too long with crappy parts.
posted by fake at 2:45 PM on October 23, 2008

I agree with everything posted so far. Some surplus/small suppliers I sometimes buy from that haven't been mentioned so far are Marlin P. Jones & Assoc., BG Micro, and Ocean State Electronics. Other hobby-robotics places include Pololu, BaneBots, and Trossen — these guys will also sell you the mechanical bits like shafts and couplers and bushings, which (as a fellow CS/EE) I've always found frustrating to deal with.

Unmodified RC aircraft servos are very easy to drive from a microcontroller; if you don't need continuous rotation, they're a very easy way to get a motor, driver, and gears in a compact box, and there's a wide range of power/weight/speed/torque/cost/lifespan/size tradeoffs available.

It's kind of fun to do all the mechanical stuff yourself, at least a few times, just to get a better feel for what's going on. But like fake says, you don't want your project to become un-fun.
posted by hattifattener at 4:31 PM on October 23, 2008

You might find something at Herbach and Rademan, a surplus store with a wide variety of electric motors, many of them already geared down.
posted by exphysicist345 at 5:12 PM on October 23, 2008

busted toy robots, cassette players, wine-bottle openers, cordless drills, etc etc. Anything that has moving parts and is battery powered probably has a motor and geartrain in it. The main trouble will be that much of the time the geartrain will be incorporated into the case, so not removeable as a discrete unit.

This. Thrift stores (especially ones where you can negotiate) are filled with things with motors in them. Most of them are AC motors (from blenders and the like), but occasionally some handheld toy will have a small DC in it. It's a great exercise in reverse engineering, and learning about the different types of motors (e.g. various phase classes). The nice thing is that if you blow 'em up, it was only a few bucks anyway.
posted by spiderskull at 6:38 PM on October 23, 2008

I would recommend picking up a couple stepper motors along with the aforementioned solarbotics gear motors. Stepper motors are nice because you can tell them "rotate +30 degrees", and they will just do that. You should be able to rip a few out of old printers and drive them with an arduino + an L293.

Here are a couple tutorials on stepper motors with arduino, also.

I would recommend picking up a copy of "Physical Physical Computing and Practical Electronics for Inventors (2nd Ed.), along with a breadboard or two.

Beyond that you may want to meet up with the local robotics club if you are interested.

(For triggering your air conditioner, what about using a tiny heater to fool the thermostat?)
posted by sebastienbailard at 7:39 PM on October 23, 2008

Suzo-Happ has arcade quality controls.
Antique Electronic Supply has cool vintage stuff.
posted by Confess, Fletch at 8:24 PM on October 23, 2008 [1 favorite]

Response by poster: Thanks for all the help so far, I like the idea of scavenging from old electronics but having sources to buy online is great too, I knew that stuff was out there, I just didn't know where to look.

(For triggering your air conditioner, what about using a tiny heater to fool the thermostat?)

I wish it was that easy! Our air conditioners just have Off/Low/Medium/High, and so while it's very hot at night and I need it on, in the morning it's very cold. The control for it is across the room from me, and I at least want to be able to flip it off from bed, if not control it automatically by temperature.
posted by DMan at 9:20 PM on October 23, 2008

For turning the dial on the A/C you're ultimately going to care most about the stall torque of the motor (especially if it's like my A/C, where the knob has detents so it goes click-click-click around the circle) -- you're going to be going from a dead stop to pushing against the max resistance of the knob. If you can borrow a torque wrench from somewhere (school shop, sometimes a friendly local auto shop) you can figure out the motor spec you'll need to meet to turn the knob.
posted by range at 8:41 AM on October 24, 2008

I haven't tried any of these so I can't vouch for them.

BG Micro

Circuit Specialists
Online Metals
The Electronic Goldmine
posted by Confess, Fletch at 9:15 PM on October 24, 2008

Response by poster: So, a related question about torque, then:

One of the servos I found said it has 90 oz-in of torque. Does that mean that it can pull the equivalent of....about 5.6 pounds with a one inch lever arm? or is it not that simple?
posted by DMan at 12:55 PM on October 25, 2008

Yup, that's exactly what it means. Or 2.8 lbf. with a two inch lever arm, and so on. The equivalent metric unit is newton-meters (N·m).

(Also, don't confuse pound-feet, which are a unit of torque, with foot-pounds, which are a unit of energy.)
posted by hattifattener at 2:11 PM on October 25, 2008

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