>>>Pi Wars 2020<<<
1Motor Upgrade
The first assembly phase already revealed some issues with the motor block:- Mounting of the wheel on the motor is needlessly fiddly
- With power electronic tested is time to add encoder and speed
PID
Objective for this phase is to focus on the motor control. Add encoder decoding for each of the motor channel and add a speed PID. Since the motor blocks are to be disassembled, mounting of the wheels on the hub is to be upgraded as well.
1.1Upgrade Plan
Order of assembly is:- Mount motor on its bracket
- Place M3 screws on the hub
- Mount the hub on the motor shaft and tighten two keys
- Insert the wheel on the hub
- Tighten the M3 screws by holding the butt of the screw with
an L shaped clamp
Illustration 1: Current Motor Block Assembly
Upgrade plan is to:- Remove step 2 of the old assembly phase
- Thread the small surviving holes M3
- Mount the wheel by bolting M3 screws of the right length from
the front
- Add encoder connector and test encoder waveform
2Upgrade Hub
Thread the small surviving holes on the hub to accommodate M3 screws.First disassemble the platform.
Drill with 2.8 and thread the small holes on the hub M3
Illustration 3: Thread M3
Threading of twelve holes on four hubs complete.
Illustration 4: Hubs Threaded
Test full assembly. Use M3x16.
Illustration 5: Motor Block Assembly
Assembly looks good, and now the process is streamlined allowing for an easier maintenance of the platform.
2.1Order of Assembly
Order of assembly is:- Mount motor on its bracket
- Mount the hub on the motor shaft and tighten two keys
- Mount the wheel on the hub using M3x16 screws
3Encoders
An encoder connector is to be added to provide closed loop motor control.3.1Connector
Holes needs to be prepared to add the connector by sucking away the tin.
Illustration 6: Prepare Holes
Connector chosen is a simple 2.54mm male pin strip
Illustration 7: Upgraded Motors
Power wires and soldered directly to the motor power pins to improve current capability.
Encoder uses four pins. Two for supply and two for channel A and B.
3.2Encoder Test
With the connectors taken care of, an encoder test was in order to verify the correct operation of the assembly and to verify the pin assignment.
Illustration 8: Encoder Test Circuit
The encoder is powered with 5V and returns two open drain outputs. Two 1K pull up resistors are used to bias the two channels. In the test circuit two sink LED are connected to the channels to visually inspect the encoder.
Video 1: Test Encoders Manually+12V motor in both
directions
4Assembly
Assemble back the motors and the hub on the acrylic base.
Illustration 9: Re-Assembled Platform
5Proto Board Upgrade
Upgrade the main board to support four quadrature encoders.Encoders are connected to PORTC of the microcontroller and are powered by the same 5V that powers the microcontroller itself.
Each encoder channel is equipped with a 1KOhm pull up resistor as the encoders of the IG32-05 motors are open drain.
Illustration 10: Proto Board Encoder Wirings
5.1Encoder Cables
Four encoder cables connects the proto board with the encoders mounted on the IG32-05 motors
Illustration 11: Make Encoder Cables
Wirings:- IG32-05 Side
- Brown +5V
- Black +0V
- White CHA
- Blue CHB
- Brown +5V
- Proto Board Side
- Black +0V
- Brown +5V
- White CHA
- Blue CHB
- Black +0V
6Conclusions
The scope of this upgrade has been to make the wheel mounting more convenient and to pave the way to add encoder feedback to the platform.
Illustration 12: Complete Wirings
Next step is to upgrade the firmware to read the encoder waveforms.
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