Accurate control of left and right wheel speed.

ChristopheLaurent commented 2 years ago

Variant

USART

Control type

FOC

Control mode

Speed

Description

First of all, I wish to thank Emanuel Feru for this incredible work. I consider an application where I would control the speed of each wheel accurately from another microcontroller. I have a couple of related questions:

1/ Reading the code, I guess that one wheel will run at speed + steer/2 and the other wheel at speed - steer/2, where speed and steer are specified as integer RPMs in USART frame, and using default config. So basically, if I set the speed to 10 and the steer to 20 in my USART command, one of the wheel should be blocked while the other wheel should run at 20 RPM, am I right ?

2/ I also noticed a smoothing filter on speed and steer, that is tunable with a set of parameters in the config.h file line 184:

`/ FILTER is in fixdt(0,16,16): VAL_fixedPoint = VAL_floatingPoint 2^16. In this case 6553 = 0.1 * 2^16

Value of COEFFICIENT is in fixdt(1,16,14)
If VAL_floatingPoint >= 0, VAL_fixedPoint = VAL_floatingPoint * 2^14
If VAL_floatingPoint < 0, VAL_fixedPoint = 2^16 + floor(VAL_floatingPoint 2^14). / // Value of RATE is in fixdt(1,16,4): VAL_fixedPoint = VAL_floatingPoint 2^4. In this case 480 = 30 2^4
define DEFAULT_RATE 480 // 30.0f [-] lower value == slower rate [0, 32767] = [0.0, 2047.9375]. Do NOT make rate negative (>32767)

define DEFAULT_FILTER 6553 // Default for FILTER 0.1f [-] lower value == softer filter [0, 65535] = [0.0 - 1.0].

define DEFAULT_SPEED_COEFFICIENT 16384 // Default for SPEED_COEFFICIENT 1.0f [-] higher value == stronger. [0, 65535] = [-2.0 - 2.0]. In this case 16384 = 1.0 * 2^14

define DEFAULT_STEER_COEFFICIENT 8192 // Defualt for STEER_COEFFICIENT 0.5f [-] higher value == stronger. [0, 65535] = [-2.0 - 2.0]. In this case 8192 = 0.5 * 2^14. If you do not want any steering, set it to 0.

` The filtLowPass32() in util.cs looks to be an IIR filter, but I'm a bit puzzled by the bit shifting... would setting FILTER to 65535 nearly disable it, assuming that the other microcontroller already filtered speed and steer upfront by another mean ?

3/ Eventually, USART outputs the speed of each wheel. However, it seems it is not the real speed computed from hall sensors, but the required speed after the filter. Is it possible to get the real speed evaluated from hall sensors ? To which extent does it differ from the required speed if I use Speed Control Mode ?

Best Regards

Candas1 commented 2 years ago

Hi,

Please check the wiki

ChristopheLaurent commented 2 years ago

Hi, I did spend a couple of hours on the wiki already, but I probably missed the answers to my specific questions. Could you please tell me which page page explain the filter coefficient, or the difference between real speed vs control speed depending on Control Mode ? Best Regards

Candas1 commented 2 years ago

I am a bit worried, having wrote some if the wiki myself, I know for sure your questions are answered. Maybe it's not visible enough. You can also you the search function of github in the repository.

Have you checked this page? There is a link to a section with common parameters

ChristopheLaurent commented 2 years ago

Hi, sure, I did check this page more than once. But the Input Command Structure description lacks a couple of details. It does not say that Speed unit is RPM, assuming that speed factor in configuration is 1.0. It is even less obvious that Steer unit is also RPM, and represent a difference of speed between left and right wheel. I had to read the code to understand it, but maybe I'm wrong so I did ask my 1st question with a numeric example. There is not much in the wiki about the low pass filter parameters as well, so I think my questions were legitimate. Anyway, I will get a second hand hoverboard very soon, I will experiment it by myself, and I may propose documentation improvements after my tests if you don't mind.

Candas1 commented 2 years ago

Don't get me wrong, I am willing to help, but I think it's all documented there, probably I am bad at documenting then.

Why are you making your life complicated with speed and steer if you want to control each wheel individually:

Is this not describing filtering good enough ?

The feedback you get is real speed in RPM:

In Speed mode, the input is the target speed, I can probably add it's also RPMs

ChristopheLaurent commented 2 years ago

Hello, I just saw your answer, and I'm very sorry for not giving you any feedback regarding it. Thank you very much for all these details. I think it answers my questions, shame on me for missing the filter chapter. Regarding Tank Steering and USART, I guess that the command sent as binary frames has the following structure in case of Tank Steering:

Start frame(unsigned int16) : 0xABCD
LeftWheel(signed int16) : Left wheel speed with range -1000 to 1000
RightWheel(signed int16) : Right wheel speed with range -1000 to 1000
Checksum(unsigned int16) : XOR checksum
The least significant byte comes first (little endian).

Am I right ? Thank you again for your nice support, but I'm afraid I will still need it as I got an hoverboard and I'm actually struggling to drive it with an ESP32...

Candas1 commented 2 years ago

Oui c'est bien ça 😜

ChristopheLaurent commented 2 years ago

Hi Candas, I've made some progress on my project and I can now drive the hoverboard motors from an ESP32. I did not manage to use SoftwareSerial for reading but HardwareSerial works fine. However, I'm puzzled by the feedback data . Here is what I get asking for a constant speed of 100 RPM using the same print as in hoverserial.ino : ... 1: 0 2: 100 3: -27 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -27 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -27 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -26 4: 29 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -26 4: 29 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -26 4: 29 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -26 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -26 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -28 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -28 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -26 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -26 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -26 4: 28 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -27 4: 25 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -27 4: 25 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -24 4: 29 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -24 4: 29 5: 3980 6: 243 7: 0 1: 0 2: 100 3: -24 4: 28 5: 3980 6: 243 7: 0 ... Cmd2 is 100 RPM as expected, the battery voltage is a little bit higher than expected (I measured about 37V instead of 39.8V) and the temperature of 24.3 degC looks to be fine. However, what is the unit of the speed in the range [24, 29] ? I understand that the sign is due to the rotation direction, but is there a mix of "revolutions per minute" and "radians per minute" somewhere ?

Candas1 commented 2 years ago

As I told you before. SpeedR and SpeedL are in rpm

Candas1 commented 2 years ago

In the form you said you use speed control mode, is it really the case...

ChristopheLaurent commented 2 years ago

Thanks a lot for your help ! I missed that CTRL_MOD_REQ parameter in config.h and I was still in VLT_MODE. The control loop works as expected with SPD_MODE.

AlfretzNehemia commented 1 year ago

Hi guys thank you for this discussion. But right now, I want to know If we select VOLT_MODE for motor control mode. The measured left and right speed doesn't get same value as the input?

Amitkor12 commented 9 months ago

Hi guys, I have a quick question about the steering part of the wheels . If I need to steer one wheel with more speed than the other, let's say a 2:1 ratio, that is, the left will spin twice the right. For this what changes should be made?

EFeru / hoverboard-firmware-hack-FOC