• Motor control

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

    Motors

    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.

    H-bridge

    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.

    NiMH

    • 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.

    Li-ION

    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.