AlkaM's blog View Details
Archive for March, 2018
Posted by AlkaM | Mar 23, 2018 @ 09:29 PM | 15,627 Views
Everything is working as it should, I had one little glitch and blew up one motor in testing but the end result is a custom esc that behaves like an esc should. Responsive and fast. Next step is to make an interface to connect to the pc and change settings.
I am still playing around with different PWM techniques. One PWM pulse per commutation might be a good way to drive motors to very high rpms and avoid any phase locking. This means that pwm frequency will change as motor frequency increases. I am lacking very high rpms motors to test properly with though. Anyway that's for future posts.
It looks a little ridiculous strapping such a big esc on but, I couldn't wait to finalize the firmware or make a normal sized esc. I had to try it out on a quad. I forgot to change the throttle min to a normal range so it starts long before the other motors but that's a minor fix.
First flight with open 32 bit ESC on a quadcopter (0 min 58 sec)

First blog post without a schematic attached but i'll dig one up to put on tomorrow. The schematic for this speed controller is in my last blog post.
Posted by AlkaM | Mar 12, 2018 @ 08:01 PM | 19,483 Views
Well, the last couple weeks of my life disapeared. I decided to try and write my own firmware for a 32 bit speed controller. I used the same processor as the KISS esc and BL_HELI32 because it makes a whole lot of sense. It was a toss up between that and the NXP Kinetis MCU as they both have the right peripherals and about the same price but I figured I would at least make hardware / software compatible with what's out there now. About a year ago I made a schematic for a firmware written by another user, DrDisorder, that was somewhere on here and faded into forum obscurity. Unfortunately it got delayed for a year. I never did get to try it. I also wanted to have regular 1000-2000us servo PWM input and tachometer output and stuff like that.
Stm32f051 firmware progress. 32 bit esc (2 min 49 sec)

Lately I got some MP6531 pre drivers in the mail. I wanted a problem for my solution and made a couple of motor drivers. One using the bb2 silabs chip and the other using the STM32F051. I decided to write firmware from the ground up, one , because I could not understand any of the other firmwares that were out there. ASM looks just bizarre to me. I had never worked with an stm32 processor before so it was a bit of a learning curve just figureing out how to initialize this and that and get things running. After the first few days of mucking around i had an open loop six step motor control going. Thats when the trouble started. I would get the motor going in a stable open...Continue Reading
Posted by AlkaM | Mar 10, 2018 @ 01:06 PM | 16,014 Views
Last year i put up a post with a silabs based blheli_s speed controller using the FAN7888. It can handle a high voltage and is quite a robust driver. After making a few designs with it i realized that it was really quite huge when trying to make smaller speed controllers. When I put together a controller using 3.3mm MOSFETS the driver was actually larger than the mosfets themselves ( see pic)! It was time for a change.
A popular option is the fd6288 from fortior. I couldn't actually find a place to buy one of these at the time, so that was out. Although it does look like a nice chip, I thought there has to be something better.
This is what I settled on.
http://www.monolithicpower.com/pub/m...531A_r1.02.pdf
The MP6531a, it was a fairly new product at the time but it has a few nice little features -- 3 big ones are.
1) An on board voltage regulator with a 5-60v( this is huge, takes away a number of components on the board, only need one reg for the MCU).
2) An on chip overcurrent shutdown and fault indicator. This reacts much faster in the event of a short than relying on the mcu.
3)Built in charge pump diodes ( 3 more components not needed).

So here are some pics of the same basic board with the FAN7888 pre driver and the MP6531 pre driver.
Uses blheli_s "i" firmware.
Schematics and Gerber files and Diptrace source all included in the zip file below.