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Old 07-13-2006, 03:20 PM   #1
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Default Question about running two batteries?

Ok I hope you guys can help me...
I havent been into rcs' since I was alot younger, but recently my wife bought me a cheap $50 walmart RC. I want to beef it up a bit using some old ryobi tools I have lying around.

I know that if I hook the 18V battery to the existing battery connection I will burn alot of stuff up. So I am going to run all of the existing stuff on the 9.6 included with the car.

I want to take the leads for the motor and wire them to somesort of relay that would allow the 18V directed to the drive motor only.

Here is my problem. It is a "variable speed" setup. (its been along time) I want to retain this but with the 18V running the drive motor.

I know it will also eventually burn the motor up too, but I have a old drill motor waiting for a retro-fit. So that is not a concern.

A new $300 car isn't even thinkable so there is no point suggesting that, but anyother help would greatly be appreciated.
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Old 07-13-2006, 04:29 PM   #2
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The speed controller will most likely not be able to handle the higher voltage and current, even if you succeed in isolating it from the rest of the circuitry.

If you want cheap rc fun, buy a used associated or losi truck or buggy. You can get a great machine that has parts available for cheap, and you will get a great deal if you buy somethign that was good in its day, but is currently considered out of date for racing. People practically give the old stuff away. You can probably buy an old buggy for $30.00, motor for $10.00, am radio for $20.00, esc for $30.00 and still have money to buy a good used (one season old) battery pack. You might be able to buy a complete car and radio for under a $100.00 and will give you more than your money's worth. If you don't smoke the motor, you will probably burn up the receiver, speed controller or strip the gears and have nothing left but a pile of junk.
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Old 07-14-2006, 10:41 PM   #3
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Drill motors and other electric tools dont use the same motors. Yes they are 540 or 550 sieze motor but the internals are different. They are a 4 to 6 pole arms not to mention the windings.
As Ice racer said you better of getting an old rc car.
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Old 07-15-2006, 12:58 PM   #4
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I will figure out how to use the drill motors that is not a problem, I wanted the pulling power they have. I was hoping someone would know enough about electronics to lead me in the right direction. I really am only asking if you can suggest a way to isolate the 18v to the drive motor and yet retain the speed control function. If it did not have speed control I would just use a relay to get it there. Is there anything like a relay that is "voltage sensitive". That is how the speed control works on this cheap car. As the voltage increases so does speed. So a relay will not work, I know. I was hoping for something similar.

Buying any car is not an option at this point, I really just wanted to use some junk I have in my shop.
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Old 07-15-2006, 02:52 PM   #5
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this is a diagram, of sorta a msc, using relays, and parts you can get from radioshack, and you lhs.

the blocks are relays, the triangles are from the 339, the bottom of each triangle is - . the wigley lines are resistors, which values i dont have the time to explain. this is a fairly simple curcuit, though it still requires parts, and time and effort. this will prove how much you are willing to go through to save the money for electronics for the r/c cars. uh, theat probably didnt make much sense, i fried my brain making up that curcuit . if you are interested in usin it, pm me, and i will give you much more detaals. and other electrical engineers: any problems with this?
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Old 07-15-2006, 08:40 PM   #6
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Just to let you know after my drag racing experience 18V would cook an R/C 540 REAL quick. A drill motor will not have any-way near the RPM that an R/C motor would. Drop in a 7.2v batt a cheap Mechanical Speedy and a tamiya sports tuned and you would go faster. Higher Voltage does not equal higher speed, yes it increases power and RPM but then you have the added problem of beefing up whats already there to cope with the stress and the stresses will be HUGE.
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