Paul & Sabrina's cheap DIY 144v motor controller - Page 138 - Fuel Economy, Hypermiling, EcoModding News and Forum

MPaulHolmes · 05-23-2009, 02:30 PM

Are you serious!? Pin compatible??? What in the crap am I doing with an ATMega8? I'm going to order a few of those.

dcb · 05-23-2009, 09:18 PM

Here is the CPU and Crystal that come with the mpguino. It is pin compatible but some of the instructions/register names are a bit different than the mega8. I'm moving towards 20mhz too FYI, couple low level timing changes as you can imagine.

I don't think it will solve slow 32 bit math though, 32 bit math is handy, but slow, have to use it sparingly. I do a lot of it but only once every 1/2 second to update the display and just do basic addition in the interrupts.

$4.11 atmega168p
http://mouser.com/Search/ProductDeta...ATMEGA168-20PU

$0.57 20mhz small crystal
http://mouser.com/Search/ProductDeta...-FOXS200-20-LF

edit: did not see a divide assembler instruction for either the mega8 or 168. Both muls take 2 cycles

tinkerdave · 05-23-2009, 09:30 PM

Regarding trying to make the controller act like an ICE car.

Most cars for Joe/Joy average driver are equipped with an automatic transmission and therefore have a torque converter that soaks up drive train vibrations/"irregularities".

Auto enthusiasts that have a stick want to feel everything that is going on with the car.

My vote is to let me know what is going on with the vehicle.

With an ICE car I am not going to try to remain stationary on a hill or the clutch will burn.
With the electric car on a hill, wouldn't it also be better to take the foot off the throttle and onto the brake?

Thanks

I B RACIN · 05-23-2009, 09:51 PM

Quote:

Originally Posted by tinkerdave

Regarding trying to make the controller act like an ICE car.

Most cars for Joe/Joy average driver are equipped with an automatic transmission and therefore have a torque converter that soaks up drive train vibrations/"irregularities".

Auto enthusiasts that have a stick want to feel everything that is going on with the car.

My vote is to let me know what is going on with the vehicle.

With an ICE car I am not going to try to remain stationary on a hill or the clutch will burn.
With the electric car on a hill, wouldn't it also be better to take the foot off the throttle and onto the brake?

Thanks

While I agree a little with what you are saying, I don't think the intent is to try and make it silky smooth as much as just very drivable, If people got a speed control that took off like a teenage girl try to learn how to drive a stick for the first time, it would turn off a lot of people from doing EV conversions.

I know when it spills my coffee on me I would say really bad words....

MPaulHolmes · 05-23-2009, 11:27 PM

I think all the testing with sometimes really badly behaved voltages and currents and overshoots because of too big of P's or I's and the micro-controller sometimes going into latchup may have caused a problem with my control section. It already was a "walking wounded" because it was in the exploded controller. I can't do any other testing until it's fixed or replaced. boohoo... I did learn the following:

Probably the best performance was one of the PI loops, but I forgot which one, and the controller is acting weird.

Another disturbing fact: I would compile a program, run it in the simulator, and it would have completely different behavior in the car. This is all very disturbing.

charlie_fd · 05-23-2009, 11:34 PM

Quote:

Originally Posted by dcb

....

edit: did not see a divide assembler instruction for either the mega8 or 168. Both muls take 2 cycles

You're right of course. Somehow I was under the impression that atmega8 doesn't do hw mul. And yes, hw div is not implemented in either of them.

MPaulHolmes · 05-24-2009, 03:32 AM

Well, I got it working again. Long story. At least it works outside of the car on the oscilloscope. I'll hook it up tomorrow, and the saga shall continue. It's still acting weird. I put in a new ATMega8. Maybe that helped?

JayC · 05-24-2009, 11:46 AM

Paul, FWIW I used a BT serial port on my robot to send all of the current time and measurements out to my PC. I would captures these in Hyperterm, save them to a text file and import into excel. I also wrote a small "menu" so I could change the constants and capture the results to see if I over or under damped.

In the attached image, the Yellow is the commanded speed. My speeds are from -50 to + 50 (that's a relative unit of measure given my encoder resolution and how fast I'm sampling them). In the example I command from 0 to 20 then to 0 to then 4 then to 0. The blue is actual measured speed.

Jay

JayC · 05-24-2009, 01:01 PM

Quote:

Originally Posted by MPaulHolmes

Are you serious!? Pin compatible??? What in the crap am I doing with an ATMega8? I'm going to order a few of those.

From what I gather you get up to 20MHz, you get 3 more PWM channels, you an external interrupt on any I/O pin, and you get a USART on your SPI and less than a dollar more.

Also have you seen the parametric table from Atmel?

Jay

JayC · 05-24-2009, 01:11 PM

BTW, there is a 20MHz version of the Mega8 too. Oh, an I forgot the 16 in 168 means you get 16K of Flash versus 8. I'd say go to the 168. Another benefit would be that you could port it to use Arduino boards versus rolling your own.

I haven't played with Arduino myself, I have all the programmers I need (STK500, Dragon, and a JTag) but the bootloader and USB functionality are more friendly to beginners. Nuts and Volts has been featuring articles about the AVR and recently the Arduino.

Not trying to confuse anything just submitting items for consideration. BTW, new Ardunios are using the Mega128 and Mega256 chips

Jay