Rotary Position Sensor + VESC

As it turns out you do not really need to make modifications to remove the hall sensor filter in order to get Rotary Position Sensors to work with the VESC. In a previous post I described how I located the hall sensor filter and removed it (read here).

Anyways, I was looking around the internet and found this blog which describes how to do it.

there is actually another port on the board you can use that is faster (hardware SPI instead of software SPI) and does not require previous mods mention here – just a change in a header file for the firmware.

By uncommenting this line in conf_general.h will enable the Hardware pins 

#define AS5047_USE_HW_SPI_PINS 1

When changes have been made you need to compile the firmware and upload it to the VESC.
The Hardware pins is located here:

It has the following pin layout  (JST–PH 2mm 7pin)

5V - 3V - GND - Clk - CSn -MOSI -MISO

To connect the Rotary Position Sensor simply connect the corresponding ports to the VESC. I use the 3V and leave the 5V empty. It also highly recommend to use a shielded cable or try to keep the wires below 7 cm to reduce electric noise.

In my earlier post I connected the AS5048A over Software SPI on the hall sensor ports and had problems reading 0-180 degrees rotor position, but 180-360 degrees worked perfect. I posted a topic on the VESC forum an got a suggestion to ignore the MSB and use 13 bits instead of 14 with the following code in encoder.c

void encoder_tim_isr(void) { 
uint16_t pos; 

spi_begin();
spi_transfer(&pos, 0, 1); 
spi_end(); 

pos &= 0x1FFF; 
last_enc_angle = ((float)pos * 360.0) / 8192.0; }

It worked perfect, I could now read 0-360 degrees rotor position with the AS5048A. The Rotary Position Sensor was running 13-bits, 8192 positions per revolution. So not optimal for a Rotary Position Sensor with 16384 positions per revolution. Please note that this fixed the problem with Software SPI over hall sensor port. 

The guy that I wrote about earlier in the post also had an alternative BLDC stack for his rover, which included a modified encoder.c with changes to keep track of the continuous encoder position. Connecting the VESC to the hardware SPI and uploaded his modified stack to the my VESC solved all problems, I was now running hardware SPI with 14-bits (16384 positions per revolution).

The AS5048A does not allow ABI interface, the AS5047P and the AS5047D does. I previously connected the AS5047D over ABI @2000 positions per revolution sucessfully. A disadvantage of the ABI mode is that it only gives a valid angle after detecting the index pulse. In SPI mode a valid angle is provided from the start.

Here is a small test of the AS5048A Rotary Position Sensor with the temporary drive system. Motor brackets are still 3D printed and not perfect (waiting for CNC Milling), therefore some annoying noises! Running VESC FOC Mode @10% Duty.

So this weekended I have been working on finishing the design of the drive system. I have updated the initial design of the 2-pulley gearing into a 4-pulley gearing. The main reason for the update is to have the ability the to achieve a lower wheel surface speed. The brackets are also designed with adjustable offsets, so each component can be adjusted to tighten the belt, or allowing a easy change off pulley sizes without redoing brackets.

Hopefully this week, CNC milling of motor brackets begins. 
In the meantime I keep the printer busy with printing pulleys. 

Sizes printed today is XL 10T, 50T and a 55T. Took a few test prints before I could find the sweet spot for the settings for a maximum belt grip.

Tonight I 3D Printed mounting brackets for the front wheels. I have acquired some cheap and simple testing wheels which will be used before I spend time and effort designing my own with proper bearings. My final wheels will also be more ball-like, so they want stuck as easy in terrain. Before doing the design I also want to test some different heights for the front wheels, with the first test wheels the robot will have a zero degree vertical angle. I want to test to use slightly bigger wheels and increase the vertical angle. If an vertical offset angle can increase the performance when cutting higher grass, meaning the cutting blade will trim the top of the grass stem at the vertical offset angle max degree and the min degree will cut the rest of the grass stem to the desired level. When the robot is up and running I will measure power consumption with different angles, check the cutting quality and compare how high grass the different angles can handle.

The 3D printed brackets came out great. Following the contours of the body and blended in quite good. This parts was also printed with PETG.

A quick and dirty assembly with all wheel mounted.

Saturday’s late night fun ended with playing around a bit. touchscreen, USB ports and external HDMI port for ease and ability to change and program on the fly when outdoors. what do you think?‬

A very quick and messy under the hood picture. This is not how it will or should look like. The final assembly will shine!

Testing the 3D printed front nose. Looks quite good. Minor adjustments needs to be done.
Printed with PrimaSelect PETG @240C, 85C bed, 3shells and 15% infill (Very solid outcome).
-Countersink need to be adjusted to cut the body. 
-The Integrated ZR300 camera need some cover on the back. 
-Check if one can use a 90 degree USB instead of a normal USB head.

Today I finished with the design of the new nose.

Before printing the new nose I decided to print only the housing for the ZR300 camera. The partly printed part came out great. The main modification from the original housing is that the housing is made deeper so the PCB can be mounted deeper allowing the USB head to be mounted in the USB socket (not possible before)

To confirm the Field of View from the the ZR300 I did a quick assembly attaching the old nose to the robot. Here is a short video on the field of view running ROS and RVIZ with a image and a depthcloud. enjoy!

So yesterday, CNC milling of motor brackets was started. 
The inside contour was finished. The outside contour is left. :)

3D printing New front nose, ready in 1h. Hopefully everything fits perfect!

First big body cover printed. The part came out great. Running PrimaSelect PETG Solidwhite at 240C. This print was printed with 0.6mm nozzle instead of the original 0.4mm. layers looks nice and even! This part was printed at 2 shells at 10% infill and print time landed on around 15h.

olala, Today all parts for the drive system is completed. 
Some parts will be welded together and then the assembly will begin next week!
I have to admit that I am a little excited :-)