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RC car not going backwards

Discussion in 'Troubleshooting and Repair' started by Russell Brooks, Mar 17, 2018.

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  1. Russell Brooks

    Russell Brooks

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    Mar 17, 2018
    My tv was used in the rain then began to play up I blew all components out with an air line and was ok I recently got it out and it won’t go backwards you can hear it trying but it then cooks the battery’s is this the speed controller needing to be replaced ???
    Please help
     

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  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Welcome to EP.
    When you can hear it trying, the speed controller seems to work and output power to the motor.
    When the batteries get hot, the current drawn is too high.
    Both symptoms together point at a blocked motor or gear. The issue is possibly a mechanical one. Can you move the drive train manually and freely in both directions?
     
    HellasTechn likes this.
  3. Russell Brooks

    Russell Brooks

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    Mar 17, 2018
    Yea drive train is fine in both directions also motor is ok also it’s definitely electrical car will go forward but not backwards the speed controller makes a noise but no power to wheels jus wires from battery begin to smoke
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    It was not obvious to me from your first post where the noise comes from.

    Seems to be a short circuit within the controller. May I assume this is a brushed DC motor? In that case the controller likely has an internal H-bridge to allow control in both directions. An H-bidge operates by activating transistors diagonally such that the motor receives either current in the forward direction or in the backward direction. It is possible, if not likely, that one of the transistors in the H-bridge has a short circuit. Obviously one of thsoe that is responsible for the forward direction. You will not notice this defect in the forward direction as this is the normal operating mode for this transistor. But in the reverse direction the transistor should be off. With a short circuit on this transistor it will also short circuit the battery, which causes the heating of the battery wires. The noise would then come from the PWM frequency of the controller.

    You can try to open the controller, locate the power transistors and check them for a short circuit. Then replace the defective transistor.
     
  5. Bluejets

    Bluejets

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    Oct 5, 2014
    Modern day controllers are not really made to be repaired.
    Process of elimation may be your best approach.
    Do you have any spares you can use?
     
  6. Russell Brooks

    Russell Brooks

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    Mar 17, 2018
    No I don’t have spares that’s why I’ve come onto here for some advise that’s what I thought it is so I’ll try a new one but I’m not sure what to get
     
  7. Harald Kapp

    Harald Kapp Moderator Moderator

    10,025
    2,138
    Nov 17, 2011
    Alas :(
    One can try anyway. You don't have to lose anything as the controller is unusable anyway. Pry it open and look for signs of overheating or obviously defect components. The H-bridge could be an integrated circuit instead of 4 separate transistors. You might be able to replace it. Nothing's lost in having a look.
     
  8. Russell Brooks

    Russell Brooks

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    Mar 17, 2018
    I think it’s a sealed unit to be honest for the cost I’ve seen there only about £8+ I can’t find a like for like replacement though I just don’t know what to go for
     
  9. HellasTechn

    HellasTechn

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    Apr 14, 2013
    You could try lubricating the motor and gears to see if it helps a bit.
     
  10. Russell Brooks

    Russell Brooks

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    Mar 17, 2018
    Motor and gears are ok it goes forwards fine and operating manually they go backwards and forwards
     
  11. Bluejets

    Bluejets

    4,052
    846
    Oct 5, 2014
    Appears the controller is a brushed motor controller model LM-406FB perhaps originally made by or supplied by, Kyosho.

    Designed for cars, has forward, reverse and brake and battery eliminator circuit (bec) of 5v 1amp.
    Suitable for 20 turn motors, Input voltage of 6.0 to 9,6v (5 to 8 cell nicad)

    That's about as much specs as I can find. Nothing about max current but I'd say judging by the mosfets (and the model number) for it to be around 40 amp.
    Apparently not much good as a controller to begin with from some of the discussions on different forums.
    Also it is old gear now so finding a manual to re-program (could be part of the problem) is almost impossible.

    It might be easier all round to get a new esc off Hobbyking.
    That is if any brushed controllers are still available, as mostly brushless are used these days.

    I'll have a bit of a look and see what is around.

    Edit:-....Had a peek on Hobbyking but as I suspected, they don't keep that much for brushed motors anymore.
    I did find one on Ebay that seems like it might do the job for you.
    Parameters seem to be in line with your existing controller.
    Specs are at the web site. Cheap at around Aus$20 really.

    https://www.ebay.com.au/itm/Hobbywi...370616&hash=item3af0c66cad:g:iCEAAOSwb3NZtp61

    Hope it helps....Cheers Jorgo
     
    Last edited: Mar 20, 2018
  12. Russell Brooks

    Russell Brooks

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    0
    Mar 17, 2018
    If that’s what you suggest as I don’t have a clue what to get I’ll go with your advise
    Thanks
     
  13. Bluejets

    Bluejets

    4,052
    846
    Oct 5, 2014
    well, I'm only going by the photo you provided.
    Surely you can see the model number on the esc.
    Bit blurry from this end.

    Would be an advantage if you could borrow an esc and try it first but anyhow,,,,
     
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