• Motor control

    Christoph Tack03/08/2021 at 21:06 0 comments


    The steering of the front wheels is controlled by a small DC-motor: 5V/300mA is the typical current draw.

    The rear wheels are controlled by a 9V DC-motor.  Voltage up to 15V has been tested and seems to work well.  Free running is 200mA, 400mA under load.  So 1A of current draw should be more than enough.


    The controller broke down and no longer wanted to generate signals on the FWD-pin.  The H-bridge was still fine.  Q1 and Q2 are TO-92 packages, while Q12 and the other transistors have a larger package.

    The operation of this H-bridge is quite simple.  Once Q1 turns on, it turns also Q12 on and the PNP-transistor on the opposite side of the bridge.  We have to take care not to make the "REV" and "FWD" high at the same time.  That would cause a power supply short circuit.

    In this circuit, there's no way to brake the motor by having Q12 and Q2 conduct, while the upper PNP-transistors in the bridge are off.

    https://cdn.hackaday.io/images/1326281616615867621.jpg : original H-bridge

  • Battery replacement

    Christoph Tack03/08/2021 at 20:03 0 comments

    The car is supposed to work with 6 AA-cells in series.  Only rechargeable cells are an option here.


    • Putting six of them in series, also adds all their source resistances in series.  When high current is drawn, the current will sink a lot, leading to power loss
    • The Goldpeak cells I use suffer from high self-discharge.  Panasonic Eneloop should be better in this respect.


    Setup 1

    1. Using a LiitoKala NCR18650B
    2. Charger : TP4056
    3. Protector : the single 8205A doesn't allow enough current.  So the over-current protection had to be bypassed.  This also disables under-voltage protection.  When someone forgets to turn off the car, the battery will be drained to death (as has happened already)
    4. Boost circuit to boot the Li-ION cell voltage to 9V using XT1208 (advertised differently).  This seems to work well.

    Setup 2

    Using the IOT-supply.