Proportional Controller EMULATOR

[ph2t]

No sweats Modjo, I'd like to thank you for pointing me in the direction of that german mods page. I've been there before but never noticed that mod in particular. (Stufenlose Geschwindigkeit just rolls of the tounge, not!)

Anyways, I've got a bit of light reading to do .

later...


ph2t.

[ph2t]

Well I've been testing the circuit using the 4N25 opto coupler and I gotta say that it works great!

The steering now holds itself well and i don't have any more issues with forcing the input pins for L, R, Fwd, Rev on the TX2 chip to ground. The advantage here is that the signal to the TX2 chip is better defined as being either ON or OFF. This should allow me to up the freq on the speed controller to allow for a smoother ride.

The big news is that I added the extra OPAMP in the comparator stage of the circuit (see schematic on 1st/2nd page, can't remember ) which has enabled me to use the dual gang POT.

What does this mean? I can now do Fwd and Rev with proportional controll(emu). I will then duplicate this circuit and run it at a lower frequency for Left & Right proportional steering(emu).

The video below shows two LEDS (one for each "channel") and how the brightness varies as I rotate the POT in either direction. At the moment both LEDS light up when the POT is centred. I just need to tweak the resistors each side of the POT so when it is centred both LEDS will be off. Turn one way causes the green LED to turn on and increase in power. Turn the other way causes the red LED to turn on and increase in power. Each LED could represent either L/R or Fwd/Rev.

Theses LEDS are a proof of concept thing. Once I sort the centre position issue out I will get some more video.

Download the 700K DivX here .

Time to sleep......

ph2t.

[Modjo]

that sounds awesome. u can actually make the wheels stay in one spot? i thought that would require a servo but i guess u can pulse it really fast.

to be honest, i only understand a little of what ur talkin about cuz my bro is the real engineer.

anyways, check out the new video on bitmod.tk of the propo speed controller. there's also a pic of the electronics linked to the controller and i think urs looks a lot easier to make.

[ph2t]

Yeah the wheels only stay centred. I'll have to make some video to be able to explain this better.

The steering is "pulsed", a short pulse means that the wheels only turn for a short time. A long pulse make to wheels stay turned for a longer time. This goes back to my first post in this thread where if you wan't to turn gradually you need to press the button on the controller repeatedly. If you wan't to turn as sharp as possible you hold the button down fully.

This idea only works because the car is moving in the fwd or backwards direction.

Again, pictures are worth a thousand words, I'll post some video tonight (hopefully).

The propo controller on bitmod.tk is quite exceptional, from what I could understand (babelfish translates like a 3 year old) the author uses the PIC microprocessor chip. One on the controller and one on the car. The original controller effectively becomes a RF transmitter and nothing more. The PIC chip encodes the signal, the controller transmits it. On the car the PIC chip decodes the signal and then uses some drive circuitry to spin the motor. The advantage of this design over mine is that it is a pure analogue voltage going to the motor on the car, not pulsed like mine is. Through this you can get better control of the car. He has a long way to go through, so far it seems to only work in one direction. Also this mod would be out of reach of the average joe (look at the circuit connected to the controller, wow!).

The advantage of my mod is that it is purely controller based, the car does't need anything changed.........

Then again, competition is good. These krauts know their sh1t.

cheers,

ph2t.

[Modjo]

PIC! those schweet. i was thinking of getting a microchip programmer. do u have one or have any suggestions on which one to get? particularly one that uses higher language.

also, shouldn't using a pic make the circuitry simpler? *oops

[ph2t]

OK, finally the circuit!

Modjo, Efaral, don't go blind!

View it in PDF format here .

Guys, I won't be able to do anymore development over the next week. We're moving house so I had to pack up all my electronics and Bits , *sigh*.

I thought I'd at least give you something to get your teeth into.


ph2t.

[ph2t]

You can omit R14, R16, R23 & R28 from the schematic and replace them with wire. They were a stuff up, not meant to be there.....

ph2t.

[ph2t]

Some of the dudes at ausmicro.com had some questions about this mod. I've answered them and thought I'd paste it here.

The throttle is proportional in both directions(Fwd & Rev).

When the pot is centred there is no signal (the trimpots R13/R15 are used to tweak the centre position for no signal). This is the same for the steering (in this case the trimpots R21/R29 are used to calibrate the centre, neutral position).

Looking at the schematic I will explain it in portions.

1) Triangle wave generator:

U1B & U1C (parts of the LM324 quad op-amp) form a triangle wave oscillator at a certain freq. This part drives the throttle so its freq is about 30-40Hz (I think). This can be set by capacitor C1.

U2B & U2C are a copy of the same osc, but in this case the value of the cap C2 is greater for a lower freq. This drives the steering, I found the steering more responsive at a lower freq (approx 6 - 10Hz)

U1A is just a reference voltage source @ 3V. This is needed because op-amps usually are run off +ve and -ve voltage sources.

2) Comparator / Pulse Width Modulator

U1D & U2A take the signal from the output of U1C and compare it against a voltage level set by the potentiometer R12. I won't go into too much detail here but when the voltage reaches a certain level @ the -ve input of U1D & U2A it outputs a positive voltage. (Bugger, this is hard to explain[xx(]. I might need to draw some pictures) This is why a triangle wave generator is used. As you turn the pot R12 it varies the width of the pulse seen at the output. Hence the name "pulse width" modulator.

The daul-gang pot (R12/R25) is the part that makes it all happen. You will see that each side of the pot is wired in opposite direction. ie: I turn the pot one way causes one voltage level to increase and the other to decrease. It is this that gives you both directions.

3) Output stage

The outputs of U1D & U2A both drive the opto-couplers which then in turn drives the transistor allowing for the pin for the TX2 chip on the controller to go to ground. At first I didn't have the opto-couplers and I was finding it hard to "pull" these pins to ground properly.


Stages 2 & 3 are duplicated for steering AND throttle. It is really stage 1 that differs (and then only in the value of caps C1 & C2).

Sorry for such a braindump, but you asked [].
I'm just waiting for uA to get back from his holiday so he can read this![]

ph2t.

[ph2t]

wow! over 2000 reads..... (massaging ego.....)



ph2t.

[Modjo]

i check this thread all the time, even if there aren't any new posts.

I'm currently searching for parts. luckily rs sold lm324 so i didn't have to order it. now all i need are some correct resistors.
did u use the exact values pht2? or did u just use one value and hook a bunch up to equal the resistance? i was also lucky enough to find dual gang pots at my local www.sciplus.com store.

[ph2t]

Yes mate, the vaules in the schematic are the values I read off the resistors once I concluded this was final. Standard 5% tolerance carbon film types, 0.25 Watt.

I have run into a problem though. Some germans contacted me and told me of a problem when trying to do steering AND throttle at the same time. Due to the way the TX2/TX2 chipsets encode the instructions of what to do (Fwd, Rev, L, R, L+Fwd, R+Fwd, L+Rev, etc....) the signal gets buggered (what a technical term!).

So I would hold off just yet on building it unless you want to help me try and figure this issue out.

The post is explained in detail at http://www.ausmicro.com in the BCG-Technical forum, look for the thread "The true extent of my madness". Quite a fitting title methinks.............


ph2t.

[ph2t]

Well, I'm making some headway... Here are some pics to show you that I am still building this. Just ran out of solder *arghhhh* , so I gotta go 'n get some tomorrow. I knew there was an Easter break for a reason!

ph2t.

[Modjo]

Interview times

So you figured out the frequency problem? I read the ausmicro posts but wasn't sure. somebody posted you had to raise the frequencies rite after you posted the new ones.

What are those round things protruding out of the board and whats the 6 pin chip for?

Just have to express my curiousity. I hope ya finish it or else i'll have 3 lm324's layin around for nothing

Sorry about the lack of help from me, I don't know much about electronics.

[ph2t]

Hey Modjo,

I hope to figure out the freq problem. As long as I keep both the steering and throttle circuits in sync and driven by the same oscillator whos max freq is about 16Hz, then yes it should be OK. I gotta build one half of the circuit at the least so I can start testing. The circuit was getting too unwieldly on the white testing board (see the earlier pics...).

Yeah the raising of the freq's was micro_amps suggestion, and a good one too.

The round things sticking out of the board are known as trimpots, these are small potentiometers (variable resistors), they are R13 & R15 on the schematic diagram. I use them to calibrate the centre posistion on the POT (R12) so as to cancel out any signal for either Fwd or Rev, this way the car isn't active whilst the POT is in the ventre posistion.

The 6 pin chips are the 4N25 optocouplers that are used to isolate my circuit from the controllers circuit. Refer to U4/U5 on the schematic. This method was much better than just connecting the controllers pins straight to the output of the op-amps.

Don't worry about the lack of help part, I hope you are learning things as we go..........

Cheers,

ph2t.

[actofgod]

ph2t, I did that proportional control icon you were wanting.

Keep up the good work.