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Old 10-11-2003, 05:44 PM   #1
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Default Decreasing resistance

Hey has anybody ever tried adding appropriate resistors in parallel to their motor? Wouldn't this allow the total resistance to drop; allowing you to run more current through your motor?

What is a ballpark figure of the resistance of a 17 turn motor?

Wouldn't this trick work very well? I know the runtime would be decreased but wouldnt there be more torque? What would be the limit of resistance as corresponds to the ESC?

Thanks
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Old 10-11-2003, 05:58 PM   #2
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UMMM resistors ADD resistance.... that is why they are called RESISTORS...... the only way to decrease resistance is by using a higher wind motor or less timing...
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Old 10-11-2003, 07:47 PM   #3
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Quote:
UMMM resistors ADD resistance....
- Wrong-
A resistor of the correct value, when added in PARALLEL to a circuit, will decrease the overall resistance of the circuit.

The equivalent resistance formula for parallel resistors is R = 1/R1 +1/R2 + 1/R3....

I don't have access to a multimeter at the moment; and I'm trying to get an idea as to why people don't do this a lot (instead of buying lower turn motors).
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Old 10-11-2003, 08:22 PM   #4
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what you'd be doing by doing that is letting some current flow through the resistor, bypassing the motor, what good is it then? you want all the power you can get to go to the motor.
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Old 10-11-2003, 08:53 PM   #5
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The resistance of the whole circuit would drop, meaning more would be pulled from the battery. Your motor would maintain the same resistance, however, so unless you could somehow harness the heat of the resistor, youd lose power
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Old 10-11-2003, 08:56 PM   #6
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Quote:
Originally posted by Herminator
what you'd be doing by doing that is letting some current flow through the resistor, bypassing the motor, what good is it then? you want all the power you can get to go to the motor.
exactly!!

you are right about lowering the resistance
but you are lowering the resistance in the circuit instead by introducing a new route for the current to flow thru in the circuit, what good it does?
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Old 10-11-2003, 08:59 PM   #7
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Quote:
Originally posted by RC Paperboy
The resistance of the whole circuit would drop, meaning more would be pulled from the battery. Your motor would maintain the same resistance, however, so unless you could somehow harness the heat of the resistor, youd lose power
There would be less Voltage at the Motor, NOT a good thing.
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Old 10-11-2003, 09:19 PM   #8
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FYI:

That is true the overall resistance of the combined additional resistor in parallel with the motor will be lower than that of the stand alone motor.

1/R_tot = 1/R1 + 1/R2 -->> R_tot = R1*R2/(R1+R2)

where if R1 = R2, R_tot = R2/2 = R1/2

So it is true that your batteries and speed controller will be flowing much more current, basically twice as much for the above example. However the current has to be split between both parallel paths and in this case each path will carry half of the total current.

Basically what it comes down to is that the voltage drop across both parallel paths are identical. Where the voltage drop is dictated by how much available voltage is present from the batteries. Where Power1 = V^2/R1, Power2 = V^2/R2. The power from your motor is dependent on it's own resistance and the amount of available voltage which do not change for either case with or without the parallel resistor. Therefore according to the simple theory the amount of power generated from your motor will be unchanged with or without the parallel resistor.

My feeling is the more current you flow through the batteries the less available voltage you will have due to the cells internal resistance. So I would advise against adding a resistor in parallel with your motor unless of course it is a second motor. But don't take my word on it sometimes the simple theory does not accurately predict some of the finer complications of actual reality.
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Old 10-12-2003, 04:04 AM   #9
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I can understand where you are coming from, but with the addition of a resistor to make the final resistance less, this will make greater demand current drawn from the battery and as a result the energy will only be transfered into heat energy across the huge (Tamiya style) resistor required.
The fact that more currnet is being drawn will not result in more power/torque as the individual resistance of the motor has not changed. You can not alk about a combined resistance then a single element of that circuit.
Remember that battery current is not supplied only drawn from!

Last edited by adyb; 10-12-2003 at 04:15 AM.
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Old 10-12-2003, 11:32 AM   #10
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If the resistor was a.... motor, it would be an advantage ! Except it wouldn't be legal at races.... But it would definately lower the resistance !
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Old 10-12-2003, 05:28 PM   #11
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Default Decreasing resistance

Guys;

Simply put, if this would work, don't you think everyone would have been doing it a LONG time ago?
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Old 10-12-2003, 07:23 PM   #12
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Default resistance

Yes I see what you guys are saying. I didn't really take the intricacies into account- I was thinking about total current, not the part that will go the motor. Interesting. And popsracer- hey you never know! Sometimes new ideas have not been tried or even thought about. But interesting overall.

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