Reducing Voltage on an RC Car Board?

Discussion in 'The Projects Forum' started by rogueleader12345, Nov 17, 2010.

  1. rogueleader12345

    Thread Starter New Member

    Nov 17, 2010
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    We are doing a Science Olympiad project that requires an RC car that uses no more than 14.4 volts and has 3 different frequencies, and we just recently acquired a car that has 4 frequencies but runs on a 19.2 volt battery. We need the board, but need it to use a lower voltage battery. We also have a lower voltage motor that will hook up with the board. We did a little searching around and saw Zener diodes. If that's the answer, how and where do we attach it? If it's not, what could we use? Thanks in advance!
     
  2. jpanhalt

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    Jan 18, 2008
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    By "frequencies" do you mean control channels, i.e., servo outputs/connectors?

    The receiver portion probably works on 4.8 to 6 volts; same for the servos. So, the board probably has a voltage regulator on it. That section is called the BEC (battery eliminator circuit) as it eliminates the need for two batteries, that is, one for the motor and one for the electronics.

    Can you post a picture of both sides of the board?

    As for the motor control, going from 19.2V to 14.4V would not be much of a problem, if your motor were rated for 14.4 V and the board does not have a low-voltage cut-off. Many, probably most do have such cut-offs to prevent over discharging the battery. Your problem then will be to find that circuit and change its cut-off voltage (probably a circuit involving resistor(s), zener diode, and/or comparator). If the board is fairly new (last few years), that function might be by a microcontroller (MCU). Some MCU systems allow the user to set the cut-off. Some even sense the initial voltage and set it accordingly. In other words, it could be really simple, it could be quite complicated, or something in between.

    For starters, please post a picture as mentioned. Also, do you have any information about the manufacturer, its location, or owner's manual? What voltage motor are you trying to run with this board? It would be a lot easier, if you had a motor that can run on 14.4V, if that is your power supply. The motor speed is controlled (probably PWM), so some motors rated for lower voltage continuous can be run on a higher voltage battery with PWM (pulse-width modulation).

    John
     
  3. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Or more simply you could get a Switch Mode DC to DC converter that will take a 12V input and produce a 18 to 20V output.
     
  4. jpanhalt

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    Maybe my answer was a little lengthy. I think there is a very good chance the controller will work just fine with 14.4V. That is the ultimate in simplicity. You may need to re-set the low cutoff.

    The only problem I see is running a motor that can't take the 14.4V, even under PWM conditions. In order to address that, we need to know more about the motor.

    John
     
  5. thatoneguy

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    Feb 19, 2009
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    As was stated by jpanhalt: the controller board runs on a lower regulated voltage. The higher voltage is used only for motor drive.

    Would need photos of both sides of controller board to make a guess if a low voltage cutoff is present, possibly not even then if it is in software.

    Make sure the motors are swapped out for motors rated for the voltage you plan to use. Using the original 19V motors at a lower voltage may work, but not as speedy.

    When you state 3 frequencies, does that mean the frequency is switchable between 3 different RF control frequencies, or 3 output control channels from the receiver?
     
  6. rogueleader12345

    Thread Starter New Member

    Nov 17, 2010
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    Hey, thanks for all the responses, and sorry about my late response. :)
    Here is a link to an album with pictures of the board.

    For clarification, by "frequency" I meant the RF control frequencies (i.e. 27.145 MHz, etc.)

    The manufacturer of the car is New Bright, but there were no specifications in the documentation we found online.
     
  7. jpanhalt

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    If it were my board, I would just give it a try. Can't tell much by looking at the pictures, except it is definitely not "high-end." Do you have an oscilloscope? If you do, see what the motor drive power looks like, i.e, maximum voltage and frequency. If you don't, create a low-pass filter (resistor in series, capacitor to ground) and see what sort of "average" voltage you are getting. You may be able to run your lower voltage motors just fine.

    John
     
  8. rogueleader12345

    Thread Starter New Member

    Nov 17, 2010
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    We'll give it a try next time we can and get back to you if need be.

    Thanks for the help!

    (And no, it is certainly not a high-end board. ;))
     
  9. rogueleader12345

    Thread Starter New Member

    Nov 17, 2010
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    Sorry for the inconvenience, but we are rather ill-versed in the electronics world, so we're going to need the information in Lehmon's terms, if at all possible. We have seen a zener diode that should work for our purposes, yet we have NO idea where it should be soldered on. Where should a zener diode be soldered onto the board? Will a zener diode even work? This Wednesday we are going to try the 9.8 V motor with the 19.2 V battery to see if it will power it, but if it doesn't we will need to know how/if a zener diode will work. Thanks in advance!
     
  10. thatoneguy

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    Feb 19, 2009
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    A zener diode will vaporize without a resistor. Trying to use one to lower the voltage for the current draw of a car would drain the batteries fast.

    You may be better off removing a few cells from your battery pack so the terminal voltage doesn't exceed 14.4 V.

    Are you using NiMH/NiCD or LiPo batteries?
     
  11. jpanhalt

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    And now you are talking about putting a zener diode somewhere? WHY?

    John
     
  12. Melnic

    New Member

    Nov 29, 2010
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    Zenor requires a resistor and that will BURN energy.
    14.4 is the peak charge voltage of a lead acid battery but won't be that under load.
    Funny requirement. [​IMG]

    RC cars now adays often run on 2 cell or 3 cell LiPoly batteries (LiPo).
    You might be better off just using a 3 cell LiPoly (fully charged 12.6V) and getting your car parts from a place like NitroRCX.COM [​IMG]

    They also have cheap 3Ch radios too.
     
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