As some of you may now, I've been tinkering with picaxes and electronics in the last 6 months. Over the past 3 months I've been designing a picaxe PWM speed controller with relay reversing and failsafing. I've had a lot of help from Ajax with picaxe code and over coming the problems with PWM on picaxe, Brett, who has spent a few late nights with me explaining about Mosfets and how to use them right, Andrew who has helped me with everything

I bought the majority of the parts to build the prototype today, I'm just waiting for 3-4 items to arrive before I can commence construction of the
Pulse 50 prototype.

Picture of the parts I have at hand:
http://www.robowars.org/forum/album_pic.php?pic_id=791

In my next post, I'll post up the specs on the controllers and the Source Code followed by the "current" dual board and single board PCB designs which anyone can make.
_________________
https://www.halfdonethings.com/

Last edited by Knightrous on Wed Aug 17, 2005 11:10 pm; edited 1 time in total

The Specs

I'm not sure how accurate these will be, but I believe it should live close to them.

50amp continous rating (3 x IRF1405 MosFets heat sinked, with 60 Amp Relays for reverse/braking)
Breaking
Polarity Protection
Failsafing (Checks Signals and will only use signals within the specified limits, not perfect)
12v or 24v Operation
12v regulated supply to relays to prevent burning out the coils on 24v
Battery Eliminator Circuit (Currently permanently on, but before any real 'production' this will be changed to on or off)

I'm probably off on somethings and some of the design is 'bad engineering' but it works.

The Source Code

The bare running code, YET TO BE TESTED.... I believe Ajax has tested it on a small scale, but his code is somewhat different to mine.

----------------------Source Code--------------------

;-------------------------------------------------------------;
;Team Distructive Technologies
;PicAxe 08M PWM Speed Controllers with Relay Reverse
;Written by Aaron Knight, with lots of help from Ajax & Spockie
;Copyright 2005 Aaron Knight
;Note: This is NOT a professional speed controller!
;-------------------------------------------------------------;
;-RC Channel Definitions
symbol fail_low = 90 ;0.9ms - failsafe below here
symbol low_on = 130 ;low activate point
symbol low_off = 135 ;low deactivate point
symbol neutral = 150 ;where motor is off
symbol high_on = 165 ;high deactivate point
symbol high_off = 160 ;high activate point
symbol fail_high = 210 ;2.1ms - failsafe above here

;-Preset Motor Parameters
symbol dutystep = 22 ; Manualy calculated
symbol min_duty = 145 ; Set for lowest start speed of motor
symbol period = 249 ; 249 = 4Khz 255 = 3.9Khz
symbol maxdutycycle = 1000

;-PicAxe Pin Definitions
symbol reciver = 1 ; Pulsein from Reciever
symbol motor = 2 ; PWM Output for Motor
symbol relay1 = 0 ; Relay 1 activate
symbol relay2 = 4 ; Relay 2 activate

;-PicAxe Register Definitions

symbol chan1 = b0
symbol temp1 = b1
symbol temp2 = b2
symbol direction = b3 ; 0 = Stop 1 = Forward 2 = Reverse
symbol dutycycle = w3


let direction = 0
;-------------------------------------------------------------;
main:
pulsin 1,1,chan1
if chan1 >= temp1 and chan1 <= temp2 then main
if chan1 > low_off and chan1 < high_off then motor_off
if chan1 <= low_on then cycle2
if chan1 >= high_on then cycle1
if chan1 >= high_off and direction = 1 then motor_off
if chan1 <= low_off and direction = 2 then motor_off
goto main
;-------------------------------------------------------------;
cycle1:
low relay1
high relay2
let direction = 1
let dutycycle = chan1 - neutral - 1
let dutycycle = dutycycle * dutystep + min_duty
gosub set_temp
goto pwm_set
;-------------------------------------------------------------;
cycle2:
high relay1
low relay2
let direction = 2
let dutycycle = neutral - chan1 - 1
let dutycycle = dutycycle * dutystep - min_duty
gosub set_temp
goto pwm_set
;-------------------------------------------------------------;
set_temp:
let temp1 = chan1 - 2
let temp2 = chan1 + 2
return
;-------------------------------------------------------------;
pwm_set:
if dutycycle > maxdutycycle then duty
;-------------------------------------------------------------;
full_return:
pwmout motor, period, dutycycle
goto main
;-------------------------------------------------------------;
duty_return:
pwmout motor, period, dutycycle
goto main
;-------------------------------------------------------------;
motor_off:
let dutycycle = 0
high relay1
high relay2
let direction = 0
goto pwm_set
;-------------------------------------------------------------;
duty:
dutycycle = maxdutycycle
goto duty_return
;-------------------------------------------------------------;


The PCB Designs

This was a whole new ball game to me, but it's one I've enjoyed learning. I picked up a free software program called Express PCB that is just a click and go style program for making PCB Designs. They also use this software for people who wish to have small prototype boards or full production runs made through the Express PCB company themselves.

Here is the Single Controller PCB
http://robowars.org/forum/album_pic.php?pic_id=792
and the Dual Controller PCB
http://robowars.org/forum/album_pic.php?pic_id=793

And that's pretty much it for now. I might chuck up a parts list and costing sheet up in the morning just for those wondering how much it would cost.
_________________
https://www.halfdonethings.com/

Hey Aaron, any chance you coul go into the fincancial side of these controllers? will you be selling them and how much a pop?
from chris
_________________
Mr "squirt"
Team Blazing Star

I won't be making and selling any to the public, I decided that after seeing the amount of flak that Brett and Jason cop over the IBC. I'm not a profession in any of this and I'm basically building the Pulse 50's for the experince of learning and hopefully for some people to have a cheap alternative that will work.

I'm looking at getting some PCB's made up for my own use, and I've found i can get 3 PCB's made for the Pulse 50 DB for under $85 shipped from the USA. That is roughly $30 per PCB. Component costs for the Pulse 50 DB is roughly $60-65 (varies on where you shop and if you buy servo leads or cut them off old servos)

So to build the Pulse 50 DB, your looking at around $90-100 in parts and probably a few hours assembly.

@Chris: I might be willing to make an exception to you and providing you pay for the parts, I'll assemble it for free. Only when the design become battle worthy.
_________________
https://www.halfdonethings.com/

i think brett and jason copped flak off the price more than any thing else.

the ibc seems handy as hell but it's a little out of the beginers price range.

So if you were to sell these for cheaper it would mean that more people could plug and play and fork out for more expencive stuff later on when needed.
you would sell a few i think

depends on what the price tag is.
_________________
For West ausies interested in robotics email me at: theoneshrug@hotmail.com
OR
dragoonarie@gmail.com
best quote ever:: "Those Gas-Turbine style warehouse heaters arent illegal, and neither is remote controlling one as far as I know."

also, you musn't overlook the fact that by selling something pro, you must constantly cope with repairs, compaints and inquiries...
so is this variable foward, non variable back? What makes it more expensive for variable reverse?
_________________
( •_•)

( •_•)>⌐■-■

(⌐■_■)

YEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAH

@Dyrodium: The Pulse 50 controllers are fully variable speed controllers in both forward and reverse. The relays only switch the polarity to the motors.

@Big Al: The IBC is extremely well priced. The Pulse 50's are by no standards even on the same level as the IBC. The Pulse 50's will only run on 12-24v, and the 24v maybe a bit limited (To do with my design, it will be partially current limited on 24v, this may be a good/bad thing).

These have been designed and will be built to suit my own needs, but I wanted to share it with everyone else incase they would like to use or modified the design.
_________________
https://www.halfdonethings.com/

ok, cool!
_________________
( •_•)

( •_•)>⌐■-■

(⌐■_■)

YEAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAH

Sounds like what Andrew built for The Aggressor at the start of last year but you didn't need to make the bit with the crystals. But there are 3 thing:
1) Are you going to add optocouplers in the input lines?
2) Since I don't think electronics companies will be happy with only doing prototpye size production runs of your boards it'll be easier to have a going at photo etching your own boards like Andrew did.
3) This is one srange sounding robot.
_________________
Get Some!!!

Secretary of the Queensland Robotics Sports Club inc.

Express PCB offers a mini board production. Where you design a board that fits in 2.25" x 3" and they will charge you a flat rate of $51 USD for 3 boards. You cannot order more then 3 at any time though.

Opto Couplers, something I haven't played with and something that would probably drive the price up higher. I may look at them in the future, but for now, this is just to suit my own needs.
_________________
https://www.halfdonethings.com/

we bought our optopcouplers for the ibc for like $5 from jaycar with the resistors .
_________________
www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

Good to see you're making some progress on your controllers there Aaron..

A circuit diagram would be helpful to cast an eye over before you commit to spending $85 getting boards made....

I suspect your main power tracks through your Fets are too small to handle the sort of current you are talking about.. remember that the IBC's circuit board has tracks 4x the normal thickness of a PCB track and they are "fat" tracks in all power-handling areas (except the "fuse" area)

It doesnt look like you have any protection against voltage spikes on the Fets (see the Tranzorb diodes on the IBC). which means any noise from the motor that exceeds 55v even momentarily will likely damage them. Tranzorbs (or TVS Diodes - Transient Voltage Supressor) arent super cheap (about $1-$2 each in low quantities), but are worth adding to help stop "unexplained" booms when a momentary high voltage spike hits things.

When paralleling Fets to increase the current capability, remember that the gate of a Fet is capacitive in nature, and putting multiple capacitors in parallel with resistors between them creates an "RC" oscillator effect that will cause the gates to "ring" when switching off as the multiple Fet capacitances equalise their charge levels.

The series gate resistor will help dampen this, but if you make it too large, it wont be able to pull the charge out of the gates quickly enough to cause a clean fast "turn off" in the Fets. This is why the IBC has the "Charge Dump" diodes on the gate drive.

Despite all this if you run the Fets at a low enough current level, then you will probably get away with it.. The switch-on and off doesnt need to be perfect since a bit of gate drive "slop" (like backlash in a gear train) doesnt matter if the power levels arent high. Like an engine, its only when circuitry is highly stressed that things need to be spot-on.

Looks like you're on a reasonable track though..

@Big AL. The IBC Price ? Heard all the whining before.. if you think its too expensive, *you* try making something that can do what it can do cheaper. It is the worlds cheapest all-in-one controller for featherweights,

I know its still the most expensive part of a robot and hard for a beginner to afford.. so what ? There is no cheaper way to do it. If you cant afford it, use relays and the Pic-Relay-Controller..

You either have to put time or money into your bot if you expect it to be any good.. they're the same thing in different forms anyway..
_________________
Great minds discuss ideas. Average minds discuss events. Small minds discuss people

I had a look at Aarons board last night and also advised that he might need the transorb diodes and have advised his to run the diagrme past you or jason before building it .The tracks are going to be beefed up with a copper wire layed over the main track i think.

Made a small modification to the board today. Shifted the Power LED to it's rightful place where it will not get blown to pieces when the controllers get 24v put into them. It now runs off the 7812 regulator. The board size has also come down to approx 52mm x 52mm x 15mm (LXWXH). Picture of the updated PCB here: http://robowars.org/forum/album_pic.php?pic_id=822

I'll be slowly rat's nest wiring up the proto during the week while I wait for the ULN2003N chip to arrive. On the topic of the ULN chip, I'm looking at finding a replacement for this chip in my design. The main reason being that out of the 8 channels, I only use 3, which is really a waste. So I'm on the look for a 12v 3 channel 8 chip which can handle loads of 500mAh-1amp.

I'll also be updating the code during the week to have the failsafing code put back in (I removed it while Ajax and I mucked around with the PWM code) and will parse that through the programmer to ensure it's going to work with out issues.

More to come!
_________________
https://www.halfdonethings.com/

ok ok spockie i know every time i open my mouth/type words i get a serve from you and all but i do agree with you bout it but if there is a cheaper thing to test and get you bot up and running it would be a good altenative.

geee feel like i'm repeting my self.

as for trying to make one for cheaper i'm going into robotics for work experience (hopefuly) so they might be able to point me in the right direction on that kind of stuff.
_________________
For West ausies interested in robotics email me at: theoneshrug@hotmail.com
OR
dragoonarie@gmail.com
best quote ever:: "Those Gas-Turbine style warehouse heaters arent illegal, and neither is remote controlling one as far as I know."