Slowing down DC motor

[Mark]

Hi, electronics has been a hobby but I'm no EE so I'd appreciate any
help. An RC motor I'm integrating into another project is too spunky
and responds too quick to the remote. I'm thinking of putting a
resistor/potentiometer in-line with the battery for a quick and easy
solution. If anyone else has any simple and quick suggestions, I'd
appreciate it. Thanks.

 

[Terry Pinnell]

Hi, electronics has been a hobby but I'm no EE so I'd appreciate any
help. An RC motor I'm integrating into another project is too spunky
and responds too quick to the remote. I'm thinking of putting a
resistor/potentiometer in-line with the battery for a quick and easy
solution. If anyone else has any simple and quick suggestions, I'd
appreciate it. Thanks.

Your motor is probably of relatively high power type, so a resistor
would have to be rather high wattage, and would get pretty hot.

Another technique (that doesn't rely on dumping excess power as heat)
is Pulse Width Modulation. Googling the groups with
pwm "motor speed control"
gave me these 256 hits:
http://tinyurl.com/663vx
the first of which is 'Help with motor speed control'.

I may well be taking a look at those myself, as I want to tame the
ex-screwdriver motor I've used in my Curtain Controller!

 

[Larry Brasfield]

Hi, electronics has been a hobby but I'm no EE so I'd appreciate any
help. An RC motor I'm integrating into another project is too spunky
and responds too quick to the remote. I'm thinking of putting a
resistor/potentiometer in-line with the battery for a quick and easy
solution. If anyone else has any simple and quick suggestions, I'd
appreciate it. Thanks.

You have not indicated how large the motor is, but unless it is
quite small or your potentiometer is rated for that use, you
are likely to damage the pot by using it that way. Using a
resistor to slow the motor will degrage its speed regulation.
That may not matter depending on what the motor drives,
(another unknown, except to you). A few 1N4002 diodes
in series would probably be better with respect to speed
regulation. You can adjust speed by adding or removing
series diodes.

 

[Spehro Pefhany]

Hi, electronics has been a hobby but I'm no EE so I'd appreciate any
help. An RC motor I'm integrating into another project is too spunky
and responds too quick to the remote. I'm thinking of putting a
resistor/potentiometer in-line with the battery for a quick and easy
solution. If anyone else has any simple and quick suggestions, I'd
appreciate it. Thanks.

If your motor is actually a servo, that will not work very well. I
believe you can buy slower servos (different gear ratio, for example).

If it's a simple DC motor- adding resistance in series will
effectively turn it into a (fairly) constant torque motor, so it will
stall very easily. Probably not what you want. What you actually want
to do is to drive it constant voltage, but with a reduced voltage.



Best regards,
Spehro Pefhany

 

[classd101]

Hi, electronics has been a hobby but I'm no EE so I'd appreciate any
help. An RC motor I'm integrating into another project is too spunky
and responds too quick to the remote. I'm thinking of putting a
resistor/potentiometer in-line with the battery for a quick and easy
solution. If anyone else has any simple and quick suggestions, I'd
appreciate it. Thanks.

Hi,

Those remote control car motors that can do ~50K RPM?

Sometimes the quick solution can cost you alot more in time in the
long run. Those motors can drain a battery pack rather quickly, I've
measured one at 6amps stall current.

The easiest and cheapest way I can think of is to use a seperate
battery pack for the motor itself and you can easily limit the number
of cells used for it if you find it too fast, they should run on 6
volts for instance. I've run them with 13.6 volts. It'll cost you a
bit more for the extra battery pack but on the bright side, when it
drains the pack all your other electronics will still be functional,
maybe that's an important feature? Certainly it's more efficient than
a resistor would be.

The best way though, would be to use PWM to gain full control over the
motor. This is how the costly speed controllers you buy for them
function as well. Its advantages are many and the only downside is the
added complexity/cost, but there's some options for you to consider.
You can also use the dedicated battery pack along with PWM, only it
wouldn't be for controlling the speed, but again to keep the other
electronics alive once the motor drains its pack. Just have both packs
grounded together if you go this route.

 

[Mark]

Thanks for all the suggestions. This is actually part of my friend's
design project. I believe it's a small RC car motor. I will try with
diodes and if that doesn't work, I'll build the PWM. Thanks!