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BEAM Pieces is a BEAM Reference Library site.
Gearmotors compared
Side-by-side
comparisons
With this page, I've attempted to pull together all pertinent data on all the DC gearmotors (and things that can be "hacked" into gearmotors) that I could get my hands on. This is by no means an exhaustive listing, but covers the most-common (and thus most-easily-found) examples.
I tested and have compared the following eleven motors:
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0.63" x 0.7" x
1.29" (16 x 18 x 32.8 mm,
22.1 g) $16 for 2 |
Commercial salvage; focus and zoom motors in LCD projector lens assemblies from BG Micro. |
These motors are only sporadically-available, but due to their high efficiency and small size are popular in the BEAM community. The last time these were available they cost $16 (US) plus shipping for two; they were available either "stripped," or as part of the original lens assembly. Details on this motor and its test results are given here. |
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0.78" x 1.2" x
1.86" (19.8 x 30.5 x 47.2 mm,
25.9 g) $3 - 10 |
Salvage; eject motor extracted from Macintosh floppy disk drive (most made by Sony). |
These motors are only available (directly or indirectly) from old Mac floppy disk drives. A bit on the bulky side, but very efficient and cost-effective at higher voltages (i.e., in battery-powered BEAMbots). Details on this motor and its test results are given here. |
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1.11" x 1.64" x
0.55" (28.2 x 41.7 x 14.0 mm,
17.0 g) $4.25 |
All Electronics; a.k.a. "mini gearhead motor" |
These motors are fairly regularly available, but aren't terribly efficient. They also use a worm gear internally, so they're not the best for BEAMbots that use motor feedback for position limiting (namely, most Nv net walkers). A reasonable replacement for servos in battery-powered BEAMbots. Details on this motor and its test results are given here. |
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0.42" x 0.77" x
0.91" (10.7 x 19.6 x 23.1 mm,
8.3 g) $3 - 10 |
Salvage; eject motor extracted from Macintosh floppy disk drives made by Mitsubishi. |
Not the most efficient, and pretty noisy (electrically), but absolutely unbeatable for performance in a tiny package. Details on this motor and its test results are given here. |
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0.8" x 1.4" x
1.6" (20.3 x 35.6 x 40.6
mm) $10 |
This is actually a "rebranded" Futaba S3003 servo. Purchased from Tower Hobbies; similar servos (manufactured by other companies) are available from Tower Hobbies, Hobby People, and other vendors catering to RC Aircraft builders. |
This servo was "hacked" to remove internal electronics, and allow for full rotation. Details on this motor and its test results are given here. |
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0.43" x 0.8" x
0.87" (10.9 x 20.3 x 22.1
mm) $20 |
This & similar servos (manufactured by a variety of companies) are available from Tower Hobbies, Hobby People, and other vendors catering to RC Aircraft builders. |
This servo was "hacked" to remove internal electronics, and allow for full rotation. Details on this motor and its test results are given here. |
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Copal gear
motor Copal |
0.63" x 0.63" x
2.1" (16.0 x 16.0 x 53.3 mm,
26.1 g) $10 - $14 |
Redistributed by way of Hong Kong hobby buffs; Andy Pang and others sell these via their sites. |
An interesting little motor; very efficient at low voltages. Comparable in some ways to the BG Micro motor Details on this motor and its test results are given here. |
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Microcassette
motor Unknown |
1.0" x 0.85" x
0.48" (25.4 x 21.6 x 12.2 mm,
10.6 g) |
Solarbotics and Electronics Goldmine; removed from microcassette drive assembly. |
Very efficient (in terms of rotation angle per unit power), but run a bit fast. They also use a worm gear for speed reduction, so they're not the best for BEAMbots that use motor feedback for position limiting (namely, most Nv net walkers). A reasonable choice at low voltage (a serial resistor on its power line would help with the speed-vs-voltage issue). Details on this motor and its test results are given here. |
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B.I.O. Bug 90 degree
143:1 motor Unknown |
2.51" x 0.88" x
0.73" (63.8 x 22.4 x 18.5mm,
27.6 g) |
"Spare" motor for the front of a red B.I.O. Bug toy (sample for testing provided courtesy of Dave Hrynkiw of Solarbotics). |
Surprisingly efficient for a "toy" motor. Gear train also includes a clutch to protect the motor in the event that the output shaft "siezes" (i.e., if the Bug gets tangled up in carpet). Details on this motor and its test results are given here. |
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B.I.O. Bug "dogleg"
177:1 motor Unknown |
1.89" x 1.65" x
0.9" (48.0 x 41.9 x 22.9mm,
27.6 g) |
"Spare" motor for the back of a blue B.I.O. Bug toy (sample for testing provided courtesy of Dave Hrynkiw of Solarbotics). |
Surprisingly efficient for a "toy" motor. Gear train also includes a clutch to protect the motor in the event that the output shaft "siezes" (i.e., if the Bug gets tangled up in carpet). Details on this motor and its test results are given here. |
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B.I.O. Bug II 224:1
motor (both dogleg and 90 degree versions
available) Mabuchi? |
1.89" x 1.65" x
0.9" (48.0 x 41.9 x 22.9mm,
27.6 g) |
Modified version of motors for second generation (Christmas 2002) B.I.O. Bug toys (sample for testing provided courtesy of Dave Hrynkiw of Solarbotics). |
An updated version of the original (2001) B.I.O. Bug motors, these are a bit more efficient (and much "torquier") than their predecessors -- as well as being easier to obtain. Details on this motor and its test results are given here. |
Note that I have, in most cases, only tested a single example of each motor. Since each motor tested may, or may not be representative of any other motor of the same design, you should take all these results with a "grain of salt."
The comparisons:
I attached each of the motors to a variable voltage power
supply, then took measurements of motor current
and output speed as a function of voltage.
Note that in many of the plots that follow, you'll see a
sharp "spike" in the motor current
data. This is due to internal "stiction" inside the motor;
the motor will draw an increasingly high amount of current
until "stiction" is overcome. Then, the required current
drops sharply as the motor starts moving. The point at which
this drop takes place is an indication primarily of the
quality of the motor bearings (better bearings have lower
"stiction," which results in a lower startup voltage),
and motor gear train.
Since one thing that a BEAMbot designer can "play" with is drive voltage (i.e., you can select your motor drive voltage in order to get the motor performance you want), all plots of performance measures are against voltage. There are 3 main variables of interest (each is addressed via plots and explanatory text on a separate page):
Motor current -- this is a traditional "quick & dirty" measure of motor efficiency, and at the least tells you what kind of drive circuitry a given motor will require. A given motor's current requirements will also determine its suitability for solar-powered vs. battery-powered BEAMbots.Motor efficiency -- this will be your best data for use in determining whether or not you want to buy a given motor in the first place. Motor efficiency will also enter into your decision of whether a given motor is useable for solar applications.
Motor speed -- this will tell you two things: (1) what the timing of your "core" circuit needs to be (short "on" time for a fast motor, longer "on" time for a slower one), and (2) what voltage you want to run your motor drive circuitry at (also enters into "core" timing). I have comparison plots of motor speed in both degrees / second and revs per minute (RPM).
Conclusions:
You have to take a number of factors into account when
it comes to choosing a gear motor -- efficiency, speed,
current
draw, size, mass, electrical noise.
All-in-all, the Nihon (BG Micro) gear motor is the best one I've tested to date. The fact that it's most-efficient at low voltages makes it an excellent choice for solar-powered bots. Unfortunately, it's only sporadically available.
The Omron floppy-eject motor is significantly less-efficient than the Nihon, and only runs at voltages at or above 2.5 V, so it's a good choice only for battery-powered BEAMbots. Still, it's more efficient than many alternatives. Unfortunately, it's challenging to mount legs to these motors, and while inexpensive, they're getting harder and harder to find (not so many old Macs with floppy drives are making it to salvage places these days). The Tokyo Micro floppy eject motor is incredibly small, and gives good efficiency at high voltages, but it's also hard to find (and very inefficient at low voltages).
For a relatively inexpensive motor, the "B.I.O. Bug II" 200:1 gearmotors are probably the best all-around deal. Much easier availability than floppy eject motors, good price, respectable performance, and a choice of two geometries ("dogleg" and 90 degree outputs). They also come prepped with holes useful in mounting them to your 'bot (something not to be dismissed out of hand).
The servos I've tested have really left me disappointed.
They are easy to find, but not terribly cheap, generate a
lot of circuit
noise (bypass capacitors
are a must with them), and are often the least
energy-efficient options for moving your 'bot. The Tower
Hobbies TS-53 is reasonably efficient at low voltages
(so it's useable for solar-powered 'bots in a pinch), if
bulky and a bit pricey for what you get. The Cirrus
CS-20bb is only useable over a small (and high)
voltage
range, and has a uniformly-low efficiency, so its small size
is really only helpful for certain battery-powered
'bots.
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