Technical Section - Testing the Motor Controller Boards
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Testing the Motor Control Boards Test Equipment To avoid blowing the expensive MOSFETS if there is a fault on the circuit board it is desirable to insert a 12v bulb and 6.8 ohm series resistor between battery and board. This can be removed after testing. For initial power-on checks also connect the small 3v test motor with a 47 ohm resistor in series. Hint: Stick a piece of insulation tape on the shaft to show which way it is rotating. Warning: This resistor will heat up with prolonged running.
Once you are happy the board is functioning correctly and the small motor can be controlled forwards and backwards at varying speeds, the bulb can be disconnected and the proper drill motors connected. These drill motors can draw currents of up to 40 amps. Initial Checks For testing, each board should be configured as a Master Board (Jumper connects top two pins). The boards are tested separately and should exhibit identical characteristics. · With Motor, Receiver, Battery, and both ICs disconnected 1. Check all components are in the correct place and are fitted the correct way round. (This is a major cause of problems. Components may be the wrong values, resistors may be fitted where capacitors should be and the 5v and 12v regulators may be reversed. Components such as diodes and electrolytic capacitors may be fitted the wrong way round.) 2. Check for dry solder joints and track bridging. (This is another major cause of problems.) 3. If you can, measure resistance between pins 1 and 3 of each MOSFET. (Note: The resistance should be greater than 1MW.) 4.
Check the heat sink is isolated (>1MW ohms between the edge of the heat sink and the large areas of copper on the board). Note: The anodised surface of the heat sink is good for heat dissipation but also acts as an insulator so place the test lead on the cut edge of the heat sink which is not anodised. 5. Check the battery plug is wired the correct way round and the red wire is connected to the positive central terminal. Note: If you connect the battery the wrong way round you will probably blow the MOSFET internal protection diodes which will cause the expensive MOSFETS and the expensive driver IC to fail the first time you try to try to stop your chariot from a high speed. Applying Power Initial power checks are done with the 12v bulb and series resistor in circuit and without the two ICs fitted in their sockets. A major fault (probably a short) is indicated by: · The test bulb illuminating. · The large 10 ohm resistor heating up. · The 12V or 5V regulator heating up. · A burning smell. Note: It is possible that if you have been touching the MOSFET pins with your fingers a temporary static charge on the gate pin can cause a MOSFET to switch on and cause the bulb to light. This can only occur without the driver IC fitted and the charge is likely to leak away in a few minutes. 6. Connect the Black test lead from your meter to the negative test point. 7. Apply power to the board from the 18v drill battery through the 12v bulb and series resistor. 8. Touch the two power regulators to check they are not heating up and be aware of any unusual smell. 9. Check approx 18v on input to board from the drill battery (End of Resistor) 10. Check 12v +/-0.5v on output from first regulator 11. Check 5v +/- 0.2v on output from second regulator (End of Diode)
12. Check voltages on IC1 socket · All pins<0.1v except · Pin 4 = 5v · Pin 8 = 5v · Pin 14=5v 13. Check voltages on IC2 socket · All pins<0.1v except · Pin 1 =12v · Pin 10 = 12v · Pin 12 = Stabilise <0.5v · Pin 15 = 12v · Pin 16 = 12v · Pin 19 = Stabilise <0.5v Inserting The PIC 14. With the battery disconnected, insert the PIC IC (18 pins) with correct orientation (Pin 1 at top left) Note: You may need to bend the pins slightly inwards to get it to fit in the socket. 15. Apply power to the board from the 18v battery through the 12v bulb and resistor. 16. Check the dual colour Light Emitting Diode (LED) lights RED. (No radio pulses being received). Note It will light GREEN later to indicate that motor rotation is being demanded. 17. Disconnect Power from board. 18. Connect the Receiver (Both Channel 2 and Channel 4 wires must be connected) 19. Switch on Transmitter and ensure that the controls are centred. 20. Apply power to board from the 18v battery through the 12v bulb and resistor. 21. Check the LED lights RED for ½ second and then goes out to indicate pulses being received from receiver. 22. Move transmitter right stick up slowly (Channel 2). The LED should glow GREEN and increase in brightness with control deflection. 23. Move transmitter right stick down slowly (Channel 2). The LED should glow GREEN and increase in brightness with control deflection 24. Move transmitter left stick to left and right (Channel 4). The LED should glow GREEN and increase in brightness with control deflection. Hint:- If the LED glows GREEN faintly with controls at neutral, adjust the transmitter trims for neutral. 25. Switch off the Transmitter and disconnect power from the Board.
If steps 22 to 25 give the correct results the first half of the board is working correctly and you can proceed to insert the driver IC. Inserting The Driver IC ONLY DO THIS IF STEPS 22 to 25 ABOVE GIVE THE CORRECT RESULTS 26. With the battery disconnected Insert the Driver IC (20 pins) with correct orientation (Pin 1 at top left) Note: You may need to bend the pins slightly inwards to get it to fit in the socket. 27. Connect the small test motor with its series resistor. 28. Apply power to board from the 18v battery through the 12v bulb and resistor. 29. Touch the two power regulators to check they are not heating up and be aware of any unusual smell. 30. Check the LED is RED (No radio pulses being received) 31. Check the test motor is not rotating. 32. Switch on the Transmitter and check the LED goes out to indicate pulses are being received from the receiver. 33. If the LED glows GREEN (the motor may also be rotating slowly) adjust the transmitter trims for neutral. 34. Move transmitter right stick up slowly (Channel 2). The LED should glow GREEN and increase in brightness with control deflection and motor should increase in speed 35. Move transmitter right stick down slowly (Channel 2). The LED should glow GREEN and increase in brightness with control deflection and the motor should increase in speed in the opposite direction 36. Move transmitter left stick to left and right (Channel 4). The LED should glow GREEN and increase in brightness with control deflection and motor should increase in speed. Note: The resistor in series with the small test motor will heat up with prolonged running and may smell slightly. Eureka It Works!
Switch off the Transmitter and disconnect power from the Board. Now test the other board configured as a master board in exactly the same way. When both boards are working correctly and identically as master boards, configure one as a Slave. Neatly tape up the lead of the Slave board Channel 4 plug as this is not used on a Slave board. Hint:- Don’t forget to remove the 12v bulb and series resistor from the circuit. If you’re having problems, or something isn’t working correctly go to the troubleshooting page. If everything is working correctly, then go on to Wiring up your robot. |
