Wheel encoder: Difference between revisions

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Wheel encoders are intended on all 4 motors, replacing the brake.
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.
Initially rear motors are mounted with encoders only. The encoders are of type AS5057 14 bit magnetic encoders.


Additionally encoder A and B signals are forwarded, but not enabled.
Additionally encoder A and B signals are forwarded, but not enabled.
The third encoder interface is used for steering - implemented using an AS5045 12 bit encoder.


==Board==
==Board==
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Potentiometer arm is connected to pin (19) A5 on Teensy.
Potentiometer arm is connected to pin (19) A5 on Teensy.
====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.
Connected to pin 22 (A8) on Teensy.


=== Debug output ===
=== Debug output ===


The Teensy constantly blinks with LED every second.
The Teensy constantly blinks its LED every second.


The output should look something like:
The output should look something like:


  $ cat /dev/ttyACM0
  $ cat /dev/ttyACM0
  enc 0.0 0 1  7905 55 5349 60 2204 1
  enc 3.3 0 1  7907 54 1747 60 2740 1 1 0 0 805364
# dropped 48 msgs
  enc 3.3 0 1  7908 54 1748 60 2741 1 1 0 0 805372
  enc 0.0 0 1  7906 55 5350 60 2700 1
  enc 3.3 0 1  7908 54 1745 60 2740 1 1 0 0 805380
  enc 0.0 0 1  7906 55 5353 60 668 1
  enc 3.3 0 1  7908 54 1752 60 2741 1 1 0 0 805388
  enc 0.0 0 1  7907 55 5351 60 3142 0
  enc 3.3 0 1  7908 54 1747 60 2741 1 1 0 0 805396
  enc 0.0 0 1  7906 55 5354 60 2700 1
  enc 3.3 0 1  7907 54 1748 60 2740 1 1 0 0 805403
  enc 0.0 0 1  7907 55 5351 60 2780 1
  enc 3.3 0 1  7908 54 1748 60 2741 1 1 0 0 805411
  enc 0.0 0 1  7906 55 5352 60 668 1
  enc 3.3 0 1  7908 54 1748 60 2740 1 1 0 0 805419
  enc 0.0 0 1  7905 55 5351 60 3740 1
  enc 3.3 0 1  7907 54 1749 60 2741 1 1 0 0 805427
enc 0.0 0 1  7906 55  5353 60 668 0
  enc 0.0 0 1  7907 55 5352 60 2204 1
 
There will be dropped messages, when no one reads from /dev/ttyACM0


Other messages is:
messages has this format:


  enc : keyword
  enc : keyword
  0.0 : intended for battery voltage (V)  (not realy tested)
  3.3 : intended for battery voltage (V)  (connected to 3.3V output of teensy - not used)
  0  : emergency switch (1=24V)          (not realy tested)
  0  : emergency switch (1=24V)          (not connected)
  1  : value from steering potentiometer (value 1 is a bit odd)
  1  : value from steering potentiometer (value 1 is a bit odd - not used)
  7906: encoder rear left
  7907: encoder rear left
  55 : magnet distance rear left (fine)
  54 : magnet distance rear left (fine)
  5350: encoder rear right
  1747: encoder rear right
  60  : magnet distance rear right (fine)
  60  : magnet distance rear right (fine)
  2700: encoder value steering
  2740: encoder value steering (2560=max right, 2755=center, 2966=max left)
  1  : valid value (steering)
  1  : valid value (as5045 steering)
 
1  : ocf from 5045 init OK
====Emergency stop====
0  : cof from 5045 no overflow if 0
 
0  : lin from 5045 no liniarity problems if 0
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.
805364 : time in ms since Teensy start
 
Line ends with a linefeed and carriage return
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.
 
Connected to pin 22 (A8) on Teensy.

Latest revision as of 14:58, 3 July 2019

Back to TerrainHopper

Introduction

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

Initially rear motors are mounted with encoders only. The encoders are of type AS5057 14 bit magnetic encoders.

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

The third encoder interface is used for steering - implemented using an AS5045 12 bit encoder.

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.

FRONT-RIGHT is changed to be steering encoder (may 2019).

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)

NB! some network cables have different color coding in the rj45 side of the connector. The coding above conforms to T568A, but the cables used on the terrainhopper uses T568B,

but as long as both cables are the same, then it should be OK.

Connection to Teensy

CLK  on all ports -> 100 Ohm -> pin 14 (CLK) on Teensy
MISO on all ports -> 100 Ohm -> pin  8 (DIN)
MOSI on all ports -> 100 Ohm -> pin  7 (DOUT)
3.3V on all ports to pin 3.3V on Teensy

Chip select:

Rear Right -> 100 Ohm -> pin 9
Rear Left  -> 100 Ohm -> pin 15
Steer      -> 0 Ohm -> pin 20
Front Left -> 0 Ohm -> pin 21

Encoder A, B

Rear Right -> 0 Ohm -> pin 18 (A), 17 (B)
Rear Left  -> 0 Ohm -> pin  4 (A),  5 (B)
Steer      -> 0 Ohm -> pin  2 (A),  3 (B)
Front Left -> 0 Ohm -> pin  0 (A),  1 (B)

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 any ground current). There is a filter capacitor of 390nF.

Connected to pin (23) A9 on Teensy

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.

Potentiometer arm is connected to pin (19) A5 on Teensy.

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.

Connected to pin 22 (A8) on Teensy.

Debug output

The Teensy constantly blinks its LED every second.

The output should look something like:

$ cat /dev/ttyACM0
enc 3.3 0 1  7907 54  1747 60 2740 1 1 0 0 805364
enc 3.3 0 1  7908 54  1748 60 2741 1 1 0 0 805372
enc 3.3 0 1  7908 54  1745 60 2740 1 1 0 0 805380
enc 3.3 0 1  7908 54  1752 60 2741 1 1 0 0 805388
enc 3.3 0 1  7908 54  1747 60 2741 1 1 0 0 805396
enc 3.3 0 1  7907 54  1748 60 2740 1 1 0 0 805403
enc 3.3 0 1  7908 54  1748 60 2741 1 1 0 0 805411
enc 3.3 0 1  7908 54  1748 60 2740 1 1 0 0 805419
enc 3.3 0 1  7907 54  1749 60 2741 1 1 0 0 805427

messages has this format:

enc : keyword
3.3 : intended for battery voltage (V)  (connected to 3.3V output of teensy - not used)
0   : emergency switch (1=24V)          (not connected)
1   : value from steering potentiometer (value 1 is a bit odd - not used)
7907: encoder rear left
54  : magnet distance rear left (fine)
1747: encoder rear right
60  : magnet distance rear right (fine)
2740: encoder value steering (2560=max right, 2755=center, 2966=max left)
1   : valid value (as5045 steering)
1   : ocf from 5045 init OK
0   : cof from 5045 no overflow if 0
0   : lin from 5045 no liniarity problems if 0
805364 : time in ms since Teensy start
Line ends with a linefeed and carriage return