Subject:
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Re: 8475 troubles
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Newsgroups:
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lugnet.technic
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Date:
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Tue, 18 Nov 2003 03:11:28 GMT
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Viewed:
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1028 times
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In lugnet.technic, Robert Seifert wrote:
> Hi there
>
> Does anybody have troubles with 8475 RC Race buggy?
>
> I bought mine last weekend (and built on the airport while waiting to pick up my
> sister ;).
> During first test ride was everything fine -- that car really goes nicely even
> in terrain -- but only for first 15 minutes. After that I observed first
> troubles - When the car starts to go, it seems like it looses signal.. Even when
> it drives (when I push it for a few centimeters, it starts), the power doesn't
> go to the motors all the time (you can hear it), The car sometimes doesn't
> steer. I hope its' beacuse of weak batteries (can't test it now as I had to
> leave back to school), but friend of mine warned me that RC units aren't really
> reliable. He is well informed as he works for TLC, so I started to worry.
>
> - How long last your batteries (let's say duracells)?
> - Did anybody have troubles with his RC unit?
>
> Thanks in advance
>
> Robert
Hi Robert
I've had the 8475 for over a year now, and I've experienced similar problems. So
has a friend of mine. From what I understand, this is what happens:
The 8475 motors are capable of drawing a very large amount of current -
see Philippe Hurbain's excellent reference on motors:
<http://www.philohome.com/motors/motorcomp.htm>
8475 motors: 3.2 Amperes vs. 0.36 Amps for the normal mindstorms motor.
Basically, when you accelerate with full throttle, you draw a lot of current
from the batteries and drain them momentarily, and they can't provide the large
amount of current anymore (remember, the current is created by a chemical
reaction in the batteries). The batteries recover after a short amount of time
(something to do with the equilibrium of the chemical reaction in the
batteries), and again can give enough current to drive. This is what causes the
stuttering - and this cycle repeats itself. This stuttering becomes more and
more frequent as the batteries get drained.
So this is what causes the problem AFAIK.
The LEGO FAQ referenced in the other post supports this theory:
"If your Racer starts to run intermittently or stutters please try changing the
batteries as these are typical signs of weak batteries."
However, I am a mechanical engineer, not an electrical or chemical one, so
perhaps someone with the right qualifications can further elaborate?
BTW, I've installed one 8475 motor in a modified 8466 off-roader, with the motor
reduced 1:9 to drive the wheels. Although it's not terribly fast, the car
accelerates well, climbs most things (I love those tires!),
and doesn't stutter. Since
1. the motor speed is reduced
2. therefore the torque is multiplied
3. so the motor doesn't need to draw as much current
4. which does not cause stuttering.
5. Pics coming soon to Brickshelf!
Hope this helps.
John Guerquin
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Message has 1 Reply:
 | | Re: 8475 troubles
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| (...) I had similar problems, and guessed it was a current limit problem (I'm an electrical engineer). I went out and bought rechargable nickel metal hydride batteries because they are rechargable and they provide more current. This helped a lot. (...) (21 years ago, 18-Nov-03, to lugnet.technic)
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Message is in Reply To:
| | 8475 troubles
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| Hi there Does anybody have troubles with 8475 RC Race buggy? I bought mine last weekend (and built on the airport while waiting to pick up my sister ;). During first test ride was everything fine -- that car really goes nicely even in terrain -- but (...) (21 years ago, 17-Nov-03, to lugnet.technic)
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