Fitting a square peg in a round hole: small DC motors

E

Elledan

[H]ard|DCer of the Month - April 2010
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Oct 18, 2001
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I've got a number of questions which have occupied my thoughts for far too long:

- DC motors usually have a smooth driveshaft. How does one attach an object like a wheel, cog or similar, made out of plastic, metal or another material to it?

- Related to the first question, how does one prevent the rest of the motor from spinning around? Friction? I don't see much in terms of mounting spots on the metal shell.

- Of an unmarked DC motor, how does one determine the maximum voltage it can safely be used at?


There, I think I'm feeling enough of a n00b now ^_-
 
(1) glue. The shaft is dipped/swapped with glue and a metal or plastic gear is pressed onto the shaft.

(2) Usually they're held in place using some sort of bracket.

(3) Apply increasing voltage until the motor starts to smell funny. Then reduce it. :D
 
gee said:
(1) glue. The shaft is dipped/swapped with glue and a metal or plastic gear is pressed onto the shaft.
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What type of glue would be best (and affordable)?

(2) Usually they're held in place using some sort of bracket.
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Do you have some examples of such a bracket?

(3) Apply increasing voltage until the motor starts to smell funny. Then reduce it. :D
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ROFL

Did you patent that method already? ^_-

Well, I guess that most DC motors are meant to be used at a voltage of around 12 V for the bigger ones, and 6 V or lower for those smaller than that. One of those unmarked motors I was talking about was 'rescued' from a battery-powered 'scissor' (cutting by hand would be an order of magnitude faster), and I seem to recall it using two AA batteries, so around 3 V.
 
mashie said:
(1) Some gears have a locking screw, if not just use epoxy or JB Weld.
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How could I forget about epoxy :eek:

They're selling JB Weld in the EU?

(2) You can use a pipe bracket if the size is right or some more epoxy.
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A pipe bracket wouldn't really work in this particular application I'm currently working on: the motor is placed in the center of a plastic O-ring/tube, so a wireframe or such (with or without epoxy) would probably work better.


Thanks for the help so far, guys :)
 
Elledan said:
I've got a number of questions which have occupied my thoughts for far too long:

- DC motors usually have a smooth driveshaft. How does one attach an object like a wheel, cog or similar, made out of plastic, metal or another material to it?

- Related to the first question, how does one prevent the rest of the motor from spinning around? Friction? I don't see much in terms of mounting spots on the metal shell.

- Of an unmarked DC motor, how does one determine the maximum voltage it can safely be used at?


There, I think I'm feeling enough of a n00b now ^_-
Click to expand...
1.) You can use the epoxy method that was already explained, or use a set screw. Most of the time I see set screws used.

2.) Custom mount. Each motor is different. sometimes they have tabs, bumps, notches, etc. to fit a bracket into. Some even have threaded holes on the business end so you can mount it to any surface with screws (provided the surface is thin enough / shaft is long enough.)

3.) Use gee's method. Seriously. Most small DC motors are going to be common voltages like 5v, 12v, 24v, etc. Just start low and work your way up!

Do you have the motor already? There are plenty of places online where you can buy small DC motors for any purpose.
 
Jicks said:
2.) Custom mount. Each motor is different. sometimes they have tabs, bumps, notches, etc. to fit a bracket into. Some even have threaded holes on the business end so you can mount it to any surface with screws (provided the surface is thin enough / shaft is long enough.)
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The motors I've got all have two holes at the 'business end'. Fortunately these would serve perfectly as mounting holes in this place. Unfortunately they're M2/2.5, whereas the smallest screws I've got are M3 :(

3.) Use gee's method. Seriously. Most small DC motors are going to be common voltages like 5v, 12v, 24v, etc. Just start low and work your way up!
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Will do :D

Do you have the motor already? There are plenty of places online where you can buy small DC motors for any purpose.
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I've got a whole pile of old DC motors I've 'extracted' from various appliances ^_-
 
gee said:
(3) Apply increasing voltage until the motor starts to smell funny. Then reduce it. :D
Click to expand...

After much experimenting I have come up with a scientific method.

1. Increase the voltage in steps letting the motor cool down in between each step.
2. When the motor burns out within 20 minutes divide the voltage by four. This is the correct voltage.
3. Aquire new motor.
 
Lots of these little motors out of battery powered devices are more like 3V, 6V or 9V IME.
 
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