Hi Scott,

There are many projects using line following cars, where you can find lots of information. Using this type of solution, but with the line across the track, so that the car knows where it is, might work.

Camerart.

 

Hi Scott,

There are many projects using line following cars, where you can find lots of information. Using this type of solution, but with the line across the track, so that the car knows where it is, might work.

Camerart.

Can you provide any links to these projects?

 

Hi Scott,

Type 'line following car' into Google, and have a look around. If you get stuck ask again.

Camerart.

 

Just to clarify my understanding:
1) The ghost cars already receive digitally encoded instructions from the controller, to set the speed. This signal is delivered via the electrical track that also supplies power.
2) This communication is one-way - no information is returned from the car to the controller.
3) The current challenge is how to vary the car's speed depending on it's position on the track. Full variable control would be great but having even 3 speed levels would be a big improvement.

It seems to me that the car itself must do the translation from the combined position information and controller signal - which will not be changing - into motor speed. Do we know how the digital code from the controller gets translated into the speed setting? I guess what I'm asking is, suppose you have solved the position information problem, what then? How would you use this information inside the car?

Sorry if these are overly stupid questions.

 

Just to clarify my understanding:
1) The ghost cars already receive digitally encoded instructions from the controller, to set the speed. This signal is delivered via the electrical track that also supplies power.
Correct

2) This communication is one-way - no information is returned from the car to the controller.
Correct

3) The current challenge is how to vary the car's speed depending on it's position on the track. Full variable control would be great but having even 3 speed levels would be a big improvement.
Correct

It seems to me that the car itself must do the translation from the combined position information and controller signal - which will not be changing - into motor speed.
I agree.

Do we know how the digital code from the controller gets translated into the speed setting?
All I know is that there is a digital chip inside each car which receives power and data packets from the track rails via the braids and outputs light control including brake lights and motor speed via variable voltage output.

I guess what I'm asking is, suppose you have solved the position information problem, what then? How would you use this information inside the car?

Sorry if these are overly stupid questions.

Definitely not stupid questions

I will post some information on a guy that designed a variable speed system using some sort of photo sensor and bar code like stickers placed on the track. Problem is he does not go into much detail at all and is not interested in making anything else available. Might prompt some discussion.

 

Here is a link to a talented German guy who has built a system to enable variable speed automated slot car ability. It is in German but Google Translate works a treat. There is also a video.
http://slotbaer.de/index.php/slotbaer-projekte-digital/28-pd132-d124/38-ghostcar-etikettensteuerung
He does not go into heaps of details on how he actually does this but I only just realised he mentions programming!!

 

There have been some really good but complicated solutions to this. What I am looking for is something that can be put together as a project by the average punter that can read a diagram, solder and owns a slot car track. Perhaps this is simply not possible but I wanted to give it a chance. Simplicity is the key here.

It's possible but you probably won't like it. In order to make this look professional, it will have to be done in the way a professional would do it, which would (in every way that I can conceive) require programming and circuit design beyond your admitted abilities. So you will have to drag yourself through a gauntlet of hard knocks learning (hey, it can be fun!), or settle for something that looks like shit, but is beautifully simplistic, like this:

 

... suppose you have solved the position information problem, what then? How would you use this information inside the car?

I wouldn't go much further with the position-sensing part - which I consider relatively easy with lots of options - until this question can be answered. If you can't override the speed control, knowing position isn't going to help.

The German in the video obviously accomplished the speed change, but there was no detail on how he did it.

 

Blue Sky: If the slot is painted with white stripes on either side, then a line following circuit could be developed. The feeds from the digital circuit would pass through a simple resistor and transistor in parallel. When the line curves away from straight, it would switch off the transistor, putting the power feed through the resistor and slowing down through the curve...

Just a concept....

 

Good point - it should be easier to break into the power circuit instead of trying to do anything with the control circuit. This means the control would be set to the highest speed, but a degree of slowing would be applied depending on track position.

 

What about if the car was programmed to travel as fast as it could around the track without deslotting (normal practice) and there was an additional circuit applying additional power to the motor (around the digital chip) depending on track position. Photo type sensor?

 

I was proposing something similar yet different.

If the car is on curved track, slow down.
If it was on a straightaway, speed up.

I think it's easier to reduce power rather than boost it.

 

Sounds like a plan. So how do we do it?

 

I think a first step would be to confirm how the motor speed changes when a resistor is placed in series with its power supply. Determine what resistance gives the desired speeds. Do we know the voltage and current we are talking about for full speed?

 

Hi,

A few ideas...
An accelerometer or a strain gauge bridge on the "pin holder" could determine even a minimal deviance from going in a straight line, so could detect the very onset of a curve and react, but I have no idea of the deceleration capabilities of slot car (with and without power braking).
It would probably require the car to be fed (or rather use) less than the max power (but still, more than the "safe" speed should be possible). Trial and error would determine the new max speed possible.

Is this a poor solution as it doesn't propel the car at the highest possible speed then?
You decide, but have in mind, that if you really made The Killer Car, any human driver would be inferior and nobody would care to race it more than once.

As an aside, you can get accelerometers with an analog output and it could be made without a µcontroller (that's not saying that it should though).
If the track has a curve that is angled/slanted (Google translate won't give me a proper term for this, hope you know what I am on about), the accelerometer will change its output accordingly, but I don't think it will detract much from the info - after all, you know the car's in a curve and that's the main thing (if not trying to beat all human drivers).
A strain gauge bridge would give a higher reading in a slanted curve as well I guess, due to the centrifugal force and it would require a bit more work (in mounting) than the accelerometer.

In the above, I imagine that the ghost car is ripped from any electronics, fed full power through the tracks and the speed determined onboard - perhaps a PID controller made with op-amps


My personal experience with slot cars is close to zero, as the only track I ever owned as a kid was extremely analog (the speeder dated it back to pre-1960, I recently discovered).


Regards,
Søren

 

Slot cars need to slow down or brake in readiness to take a corner. If the decision to slow down was left until the car began the turn it would almost certainly deslot. In this case the breaking efficiency is adjustable thanks to the cars digital chip. In an analog car breaking is controlled by joining the two motor terminals together through a resistor (fixed breaking effort) or a pot (adjustable breaking effort). This is all taken care of inside the analog controller.

Soren I believe the term you were looking for to describe an angled/slanted track is "banked"

 

So the plan might be to run multiple power feeds "around" the cars digital chip. Additional feeds can run through a resistor (value to be determined) to provide the desired motor output. I think we might be able to start with 3 speeds.

1/ could be the car programmed to travel the track as fast as it can without de slotting which is normal practice
2/ could perhaps be somewhere between speed 1 and full speed or power (resistor required)
3/ could be simply full speed or power (no resistor required)

This sounds good to me so far but I think the next piece of the puzzle is the hardest...how do we switch between the individual feeds?

 

Slot cars need to slow down or brake in readiness to take a corner. If the decision to slow down was left until the car began the turn it would almost certainly deslot.

Human reaction times are usually quoted in the range 0.5s..2s (depending on age, state of rest, amount of alcohol in the blood etc), whereas the bandwidth of eg. the old(ish) ADXL330 is up to 1600Hz, making it 800 times (or more) faster than even the sharpest human driver.
As I don't know the speed of modern slot cars, i can't say what that means in distance, but I guess that half a second may equate to quite a bit of track?
Less than a millisecond however...

I'm not trying to "sell" you my ideas here, but the more informed you are, the better choice you'll provide for yourself.

[...] In an analog car breaking is controlled by joining the two motor terminals together through a resistor (fixed breaking effort) or a pot (adjustable breaking effort). This is all taken care of inside the analog controller.

Power braking is giving controlled bursts of reverse power and it's faster than just shunting the motor terminals (only barrier is skidding).

Soren I believe the term you were looking for to describe an angled/slanted track is "banked"

Thanks! Any day you learn something new is a good day


Regards,
Søren

 

I go back to my original concern, that the features you want would require programming a mirocontroller And may even require reverse engineering (or obtaining detailed technical documentation of the digital controller used in the cars).

I hear you about your concern that the car must reduce its speed before it enters a curve. That says to me that my idea of using a line following algorithm would not be successful. I go back to your idea of using bar code stickers. However, while fully reading a bar code and reacting to it will require progrmming, a simple stripe would not.

So my current idea is to paint (or stick) a white stripe on one side of the track to tell the car that it is entering a curve. And a second stripe on the other side of the lane to tell the car it is leaving a curve and to resume speed. The car would have a sensor mounted under the bumper on each side. The sensor I previously linked to could still work in this situation.

Then, a circuit with a flop flop to remember which state the car is in (reduced speed or entering/in a curve and leaving a curve/entering a straightaway or resume speed.) is used to switch resistance in and out of the motors power supply. Here is a concept circuit. Since my Spice does not have models for phototransistors, I used simple spst switches to simulate them. The component values were only used to test the concept model; @wayneh 's comments regarding determining the resistance values and testing to see if this approach even works are important to remember. I didn't have that data, so just worked on the concept.



The bypass switch bypasses the sensors, so the car could be programmed to run as fast as it could without deslotting using a regular controller or however ghost car is controlled.

 

An excellent start. It might further be possible to count stripes that are detected close together, to give another speed level. Use the output of the counter to control, say, 2 transistors in the manner above, giving 3 speeds instead of two.

But, for testing and proof of concept of a prototype, starting with 2 speeds makes good sense. If it works, refine it to more speeds or more reliability or whatever is needed once you see how it goes.