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Join Date: Jul 2009
Location: United States
Posts: 42
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RC car circuit

10/24/2009 5:58 PM

Hello,

I am attempting to modify an existing RC Car receiver circuit so that it provides full power (3xAA ~ 4.5v) for forward and reverse, and a reduced voltage (2xAA ~ 3v) for turning.

It is a simple two-motor RC that drives the motors opposite one another for turning - zero turn radius - and being that they currently go at the same speed as when going forward/back, it actually turns too fast.

My plan was to provide the (+) bank of transistors that feed the motors 3V consistently, and when the forward or reverse was pressed to activate a transistor and feed the bank the full 4.5V.

I tried connecting a lead from one of the diodes (marked in green; that meters +2.0V when either forward or reverse are pressed) to the base of an NPN transistor to supply the full 4.5V, but wasnt successfull.


Can anyone suggest a way to accomplish this fairly simply?

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Guru
Popular Science - Weaponology - New Member United Kingdom - Member - New Member

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#1

Re: RC car circuit

10/25/2009 3:24 AM

I long since gave up messing with anything that doesn't have a circuit diagram...
I generally found it was easier to scratch build.
Keep the receiver part, identify the outputs from it for the various conditions and then design/build the circuit you actually want. (mind you, I generally then lose the circuit diagram)
It gives better flexibility for future development too.
Sorry if this isn't what you want to hear.
Del

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Guru

Join Date: Oct 2009
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#2

Re: RC car circuit

10/26/2009 4:34 AM

One problem with your proposal is the situation when the transmitter is used to give forward/backward and steering commands simultaneously. If the RC system uses proportional control, you are better off working on the transmitter than the receiver, by limiting the extent of the steering command.

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Power-User
United Kingdom - Member - Hobbies - HAM Radio - G7TSP Engineering Fields - Electrical Engineering -

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#3

Re: RC car circuit

10/26/2009 10:15 AM

A couple of series diodes?

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Anonymous Poster
#4

Re: RC car circuit

10/26/2009 11:04 AM

When your car turns either way, the two motors have an oposite polarity to one another.

Find the transistor outputs from the RF decoder that control the motors and XORthem; use the gate output to control a PWM before the DC BUS (e.g. 1=30%, 0=100%).

You'll need basic skills in electronics. If you self sufice at it, then design the circuits yourself or google the most basic schematics for each.

Yahlasit

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#5
In reply to #4

Re: RC car circuit

10/27/2009 1:29 AM

Thanks for the suggestions,

I did put together a 555 timer circuit for pwm-ing the voltage I wanted, but it seemed excessive for what I was doing. I was able to get it to work after sufficient head smashing using a series of npn's, diodes and a relay. Its not ideal by any stretch, but its doing what I want.

Thanks again for the suggestions - and lastly, can anyone recommend sites to look at for a person who is interested in getting into RC stuff more seriously?

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