Subject:
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Re: Motors & handyboard
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Fri, 14 Feb 1997 20:19:32 GMT
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Original-From:
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Chuck McManis <CMCMANIS@FREEGATE.NETsaynotospam>
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Reply-To:
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CMCMANIS@FREEGATE.stopspammersNET
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Viewed:
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3080 times
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[meta comment, messages without carraige returns are hard to read...]
Oriol de los Santos Vidal wrote:
>
> Yesterday I tried to run a motor out of the HB. First I tried how
> much current it needed with a multimeter and a 5V power source ...
> The result 75mA.
Unfortunately this is the LEAST amount of current the motor will
draw when operating. You have measured the 'unloaded current'.
Now, while you have your motor running, grab the shaft between
your fingers and stop it, and measure that current. That is the
MOST current your motor will draw, its called the 'stall current'.
The physics are that when the motor stops turning, and its coils
are fully energized, the resulting circuit can be analyzed as a
simple DC resistor. If you have a milliohm meter, measure the
resistance of the motor's coil. To work on the handyboard reliably
that resistance must be 5 ohms or greater. If it is between 3 and
5 ohms, it will work as long as you don't let it stall for too long
and under three ohms and it will over power your board. A typical
R/C car motor (cheap R/C car from radio shack) will have about 1.5
ohms resistance (using ohm's law that is 9.6/1.5 or 6.4Amps of stall
current. One of the expensive R/C car motors will have a coil
resistance of .25 ohms or less (9.6/.25 = 38.4 Amps!) The 9.6 I've
used is the Handyboard battery (motor) voltage.
>
> When I tried to run the motor from the HB, after turning on the
> motor at low speed (motor (0,20);) to make sure I wasn't sending
> to much current through the motor drivers, the motor ran for a
> second and then the HB power led lighted and the board was reset.
> Is that a sign that the power the motor needs is much higher than
> the HB can supply. In this case I would expect the motor drivers
> to burn, but not to cause the HB to reset.
It can be a sign that you are drawing too much current, however it
is more likely that the noise generated by the motor caused the
board to reset. If the motor chips are not hot to the touch, then
it is the latter. Possible cures for motor noise are a capacitor
across the motor terminals and running the motors from a separate
power source.
--Chuck
--
cmcmanis@netcom.com http://www.professionals.com/~cmcmanis
All opinions in the non-included text above are the sole opinions of
the author.
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Message is in Reply To:
 | | Motors & handyboard
|
| Yesterday I tried to run a motor out of the HB. First I tried how much current it needed with a multimeter and a 5V power source ... The result 75mA. When I tried to run the motor from the HB, after turning on the motor at low speed (motor (0,20);) (...) (29 years ago, 14-Feb-97, to lugnet.robotics.handyboard)
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