Wheel encoder

Revision as of 14:36, 14 February 2019

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Introduction

Wheel encoders are intended on all 4 motors, replacing the brake.

Initially rear motors are mounted with encoders. The encoders are of type AS5057 12 bit magnetic encoders.

Additionally encoder A and B signals are forwarded, but not enabled.

Board

Encoder interface is I2C and interfaced using a Teensy 3.1 processor, as shown in figure 1.

Figure 1. Breadboard with Teensy 3.1 and 4 8-pin connectors to the AS5047 boards. The board also holds the needed voltage dividers for battery voltage and steering potentiometer.

Encoder interface

Signal wires to encoders has a 100 Ohm serial resistor (CLK, MISO, MOSI (and CS on rear encoders))

• pin 1: CLK (green-white)
• pin 2: Chip select (green)
• pin 3: MISO (orange-white)
• pin 4: GND (blue)
• pin 5: MOSI (blue-white)
• pin 6: 3.3V (orange)
• pin 7: B quadrature signal (brown-white)
• pin 8: A quadrature signal (brown)

Wires using unshielded network cable (cat-5)

Voltage dividers

The Teensy AD converter for battery voltage and steering potentiometer uses 1.2V reference. The signals therefore needs voltage dividers.

Battery

The battery voltage divider uses a 27kOhm and a 1.2kOhm, allowing up to 28.2V to be measured. (in (optional) ground connection is mounted a 100 Ohm resistor to avoid or limit ant ground current). There is a filter capacitor of 390nF.

Steering potentiometer

The steering potentiometer is supplied from 3.3V supply (through 100 Ohm resistors). The arm is then voltage divided using a 20kOhm and 11kOhm resistors, with a filter capacitor of 330nF.

Emergency stop

This is intended to inform software that emergency stop is pressed - pt. only one channel for rear emergency stop, but maybe the remote should be separate.

A voltage divider is added on the emergency line with 20kOhm and 4.7kOhm, this should give a switch voltage of about 7V - assuming supply from 24 V.