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Soren Winkler Rasmussen
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Greetings fellow slot car racing fanatics


I've put up a draft CarDCC hardware requirement specification on a website kindly established by Randy Brown ... thank you for your kind help.


I'm hoping to get some feedback from you about what is god and what is bad, or alternative solutions that you feel would provide a better solution.

Please feel free to comment on any aspect of the proposed digital system.
Your help in making this system the ultimate slot car experience, is highly appreciated.
 

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Soren Winkler Rasmussen
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355 Posts
Discussion Starter · #3 ·
QUOTE (drummer @ 9 Jan 2005, 06:50)This is a good start Soren, well done. Particularly exciting is a power base that could easily switch betwen analogue and digital racing.
<{POST_SNAPBACK}>Thank's a lot drummer.


If there are areas in the specification that needs a better (perhaps non technical) explanation, don't hesitate to ask.

I'm wondering if I have been a bit too technical in some of the descriptions?.


We need to get the specification done in a way that everybody can read it and form their own opinion. Not everyone is into electronics, but their slot racing experience is just as valuable to this project.


So please let me know if I need to explain parts of the specification in a different way.
 

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Soren Winkler Rasmussen
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355 Posts
Hi there


I was thinking about an alternative way to communicate between car and lane change driver that could overcome some of the potential problems of the IR opto link used by Scalextric.

The first idea was to use the guide blade for car id coding. Here is a draft design of a CarDCC guide blade, that would allow up to 16 cars on the track. I've used the normal 18,5x5,5mm Scalextric guide blade as basis for the design, but the overall size is not important ... just the relative dimensions.

IMO there are the following advantages to this solution:

1) Analog cars doesn't need to be modified to race in analog mode, where you race one car per lane. The lap and sector timing will work just as in digital mode. The guide blade address could be ignored, and the system could use the lane address instead.

2) You need no sensor electronics in the car, you just make some slots in the guide blade.

3) The sensor output can be used for an extra LED light control instead?, like flashing headlights or the flashing lights on a safety car.

4) There's no need to drill a hole in the car body.

5) It's easy to fit the car controller in the car, because it can be placed anywhere.

6) Cars without free space behind the guide blade can be converted just as easy, like the narrow F1 cars or cars with a front motor.

7) It doesn't matter if the car is sliding, so you don't have to have a straight section before the lane change.

8) The solution has low sensitivity to stray light with a fork sensor arrangement. Outdoor racing should not be a problem.

9) The fork sensor arrangement can cover different lane spacings with the same sensors. It should be easy to cover several centimeters distance between LED and photo sensor in the fork arrangement.

10) In digital mode the system could program the address automatically by reading the guide blade address. This reduces the number of programming keystrokes on the track controller. You just switch on programming mode and drive the car across a lane change, and the system will do the rest (saves you the inconvenience of entering the car address on the track controller).

I think that this method of detections has been tried in real life ... I vaguely recall reading about a system with something along these lines somewhere?.

What do you all think about this?.


Edited:
Oops ... I forgot the best argument: It's a keep-it-simple solution, and I really like that.
 

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Soren Winkler Rasmussen
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355 Posts
I found the review.

QUOTE (SWoRd @ 9 Jan 2005, 13:45)... I vaguely recall reading about a system with something along these lines somewhere?.It's the Carrera Pro-X system.


Looking at the pictures they have a huge guide blade with four square holes. But they also have an IR opto link ... why is that?.

Perhaps they don't use the square holes to identify the car?.
That should be easy to answer for someone with a Pro-X system ... looking at the holes in the guide blade, are they similar, or is there a distinctive hole pattern on each cars guide blade?.

The guide blades look huge, but I guess that the turn radius is larger on a Carrera track.
 

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Soren Winkler Rasmussen
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355 Posts
Discussion Starter · #6 ·
A bit of news (although nothing spectacular
)

I received the long awaited motor controller today.


Althoug my telephone camera is really lousy at taking close up pictures, I thought it could at least give you an idea what the prototype CarDCC controller looks like.


I'm still waiting for the four rectifying diodes, but I expect to have the first car controller assembled any day now. The embedded software is still far away though.

I've checked the overall size, and the controller will fit into the sidepod of a formula one car. I don't know if there are cars on the market with less space inside, but the dimensions of the controller are 15x23mm.
 

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Soren Winkler Rasmussen
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355 Posts
Discussion Starter · #10 ·
Hi Astro

Great feedback.

QUOTE (astro @ 11 Jan 2005, 17:11)Fabulous work as always. At first the DOC document did not come up, but it did today.Thank you.


QUOTE Suggestions and comments detailed. Obviously this is a list of things that I feel deserve comment or could imho be done differently, it is not intended to come over negatively.Don't worry ... I won't take it personally.


The reason I put the specification up here, is because I want the weaknesses in the system design to be identified before I get too far in the design process.

QUOTE Firstly regarding the guide method of ID -

This would work elegently for me on the old scalextric blue guide system - simply snap out the guide number 7 and click in the guide for car ID 12 when needed. But changing the ID of cars with other guides can be fiddly. The new scalex type is screwed in from inside the car, others have the wires soldered to the braids or use those bullet things - I hate changing those guides cos the braids never go back the same!You certainly have a point here ... perhaps making slots in the guide blade is more cumbersome than mounting the LED sensor in the bottom of the chassis?.

I'll try if I can think of a better idea ... perhaps if we could design a system where you can mount small photo blockers in the guide holes or slots, and set the address without the use of tools.

That way you always have to make 4 holes or slots, and block the ones you don't use. I think the major problem would be to make a design that won't fall off in the slot, but who knows ... it might be possible.


QUOTE also - the variety of guide types means that the system presumably would not come with a set of guides, but people would have to saw their own. I am just trying to envisage how this would work in clubs where the cars need to be recoded etc.Yes, I agree ... we need someting that's simple to configure.

IMO the ability to place a lane change anywhere, regardless if the cars are sliding, is rather nice though.

QUOTE Sector Timing -

It is my understanding that you are planning to use the LCs to divide the track into sectors. Since at the moment people are generally thinking of evenly spacing LCs, this makes a lot of sense. However, maybe a sector track should be a seperate thing to an LC? It would make track/sector design more flexible (eg you might want to set up a couple of sector dividers so you can time the velocity along the long straight of your track)Yes, I thought we could use the sensors that have to be there for lane change, for lap and sector timing as well.

There should not be any problems in placing lane change drivers anywhere on the track. If you only need the timing functions, you can leave the solenoid outputs unconnected. Also there should be no practical limit to the number of lane changes you can put on the track


We might even be able to do something clever with a lane change sensor at each pit garage in the pit lane?.

QUOTE High Voltage Low current -

I understand what you are saying and the advantages of this. Thers a few things I don't quite follow:
Say a given car in analogue goes top speed at 12 volts DC, drawing 2 amps. power used = 24 watts, and it goes at a certain speed.Exactly.


QUOTE Now with the high voltage system, we are sending the car 24 volts, but only allowing it 1 amp (again 24 watts) Is the chip inside the car supplying the motor with 12 volts 2amps, or 24 volts 1 amp?This is a bit tricky, but I'll try to explain it. Please bear with me if this doesn't come across in a logical way.


The car will deliver 24V 2A 50% of the time. If the signal change quick enough, the motor will see this as 12V 2A 100% of the time.

This is because a motor forms an inductive load. If you apply a voltage to an inductive load, the voltage will appear without delay, but the current will rise slowly according to the time constant of the inductance. Likewise the current will disappear slowly when you remove the voltage (the inductor will continue to deliver current while the magnetic field in the inductor collapses).

This is opposite a capacitive load, where the current appears immediately and the voltage rises slowly.

The power supply will deliver 24V all the time, but it will deliver 2A 50% of the time, and 0A the other 50% of the time. In average this will draw 1A from the 24V power supply.

QUOTE If the chip is supplying 24 volts but limiting the current, then the car motor will be running in a current starved situation. Even though it is recieving the same power, will it behave the same? and what about at 22 volts? Has this method of motor control with current starvation been tried in the analogue (or digital) environment before it is implimented?If the voltage drops to 22V, the car regulator must increase the duty cycle from 50% to 55%.

QUOTE I just know that home racers get frustrated with power when there is not enough current, and in analogue the best driving is unlimited amps, adjust voltage for top speed..You are right. I think that adressing the power supply and power sharing issues, wil be one of the most important features with the new CarDCC system.

QUOTE Hand controller connector

jacks or mini jacks - although cheap and small, are not the most reliable of connectors, and the cheaper sockets sustain wear and corrosion quite quickly. Something with seperate pins (XLR/cannon connectors are excellent but pricy and bulky - telephone connectors as used by SCX and Carrera are probably the best except they are fiddly to wire) would in my opinion provide better longterm reliabilityIt's certainly possible to use other connectors ... I'll check if it's possible to make a dual mounting option, so that you can chose if you want minijacks or RJ telephone connectors.

Those vere very usefull inputs sofar.
 

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Soren Winkler Rasmussen
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355 Posts
Discussion Starter · #13 ·
QUOTE (drummer @ 15 Jan 2005, 17:07)Hi Guys, just thought Id say, I think the chassis mounted sensor is really a simple, cheap, effective and readily available solution, I'd stick with it.I'll check out if it's possible to implement both options in the prototype lane change controller?. That would allow us to evaluate both methods.
 

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Soren Winkler Rasmussen
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355 Posts
Discussion Starter · #14 ·
Hi GB
QUOTE (gboulton @ 11 Jan 2005, 17:17)Downloaded the spec doc today, will give it a good reading some time this week, per our discussion in the other digital thread.That's great.
... I'm looking forward to hearing your opinion.
 

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Soren Winkler Rasmussen
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355 Posts
Discussion Starter · #15 ·
Hi Astro
QUOTE (astro @ 11 Jan 2005, 17:42)My understanding of the track drivers is that each lane is kept electrically seperate, but in digital mode, they are fed (from different chips) the same signal. Part of the advantage of this solution is to make it easy to swap between digital and analogue?Yes, making the switch from digital to analog by software control is one of the advantages.
Another advantage is that you increase the current capacity of the system each time you add another output driver.

QUOTE Whilst this adds flexibility in some ways, the track pieces from all manufacturers will allow unusual topographies of digital track. The circuit can narrow to one lane in places, and widen to 3, or 8 if you so wish, in places. Pit lanes are a vital part of it.It would be possible to connect all tracks together, if you don't want to use the extra power available from multiple drivers.

One of the reasons for choosing a multiple driver approach, is that it's more difficult to design a 30A short circuit and overload proof driver, than three 10A drivers.

There are also problems involved with handling 20A or 30A on a single PCB.

The modular approach will allow you to add an extra track controller to power the lane changes, the pit lane and the track signal lighting. That would free the other track controllers of the burden of supplying anything but the cars.

QUOTE Assuming most people will want/accept 2 lanes across the start/finish line, how does the proposed system cope with such circuit designs?I would prefer a flexible system concept, that would allow the price conscious buyer to stick with one track controller. At the same time this shouldn't prevent those that want to improve the performance of their system, to add more units that would improve the capacity and power handling capability of their system.
 

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Soren Winkler Rasmussen
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355 Posts
Discussion Starter · #18 ·
Hi Drummer
QUOTE (drummer @ 17 Jan 2005, 06:41)Gee Sword looks greatThank you for the kind words.


QUOTE can you tell me what controller chips you have decided to utilise?In the prototype car controller I'm using the Atmel Tiny13 microcontroller and the Motorola MC33887 motorcontroller.

Here are the latest descriptions of the prototype CarDCC hardware (see under "Digital slot car controller").
 

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Soren Winkler Rasmussen
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Discussion Starter · #20 ·
Hi Beppe
QUOTE (Xlot @ 17 Jan 2005, 20:49)It does look impressive, SørenThanks a lot.


QUOTE Could you please explain in lay words where output current measurement would be available in the car controller ?I'll give it a shot, but don't hessitate to ask again if my explanation sounds like nonsense.


The motor controller U3 has a current feedback output FB on pin 20. This output will source the motor current divided by 375. If the motor draws 5A, the FB output will source 5A / 375 = 13,33mA.

By connecting a 100Ω resistor from FB to ground, we convert this current to a voltage. Using Ohm's law we get U = I * R = 13,33mA * 100Ω = 1,33V. In other words: when the motor current goes from 0A to 5A, the voltage on the FB pin goes from 0V to 1,33V.

This voltage is fed to an analog to digital converter input PB5 on the microcontroller through a 10KΩ resistor. The 10KΩ resistor will not influence the current measurement voltage, because the ADC input as a very high input impedance (typically 100MΩ).

The microcontroller will be able to measure this voltage by using the internal ADC. It can then calculate the motor current by using Ohm's law I=U/R:
Motor current = 375 * FB current
... knowing that I = U / R and the voltage U is measured by the ADC, we get:
FB current = ADC / 100Ω
... hence:
Motor current = 375 * ADC / 100Ω = 3,75 * ADC

Example: the ADC measures 1,33V ...
Motor current = 3,75 * 1,33 = 5A

The 10KΩ resistor will allow you to use the PB5 signal for debugWire in-circuit emulation when you're programming or debugging the microcontroller software. The only draw back is that you can't measure the motor current when debugging.

The C2B capacitor is only there to filter out some high frequency noise on the current measurement signal.
 

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Soren Winkler Rasmussen
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Hi Beppe
QUOTE (Xlot @ 18 Jan 2005, 08:57)Thanks a lot, Søren - I think I got it (apart from debugWire in-circuit emulation !!)Great.


... the in-circuit emulator (ICE) is a debugging equipment you attach to the microcontroller, that allow you to download software, view the internal registers, RAM and ROM, singlestep your program one instruction at a time and set breakpoints when the code reaches a certain point.

In short, the ICE allows you to look inside the microcontroller and change registers and program execution ... a very nice tool for debugging.

... and an Olimex AVR ICE cost only $39,95.


QUOTE So, will your motor controller have current limitation (PWM override) as a way of defining car classes ?Yes, the current limitation is software configurable ... that's the big advantage by using this method compared to the hardware controlled current limitations.


QUOTE Or is there another output overcurrent protection ?Apart from the software current limitation, the MC33887 motor controller also have a built in hardware current limitation. The hardware current limit will cut in at 6,5A, and is there to protect the motorcontroller from overload (such as short circuits), if the software limiter isn't fast enough.

QUOTE I realize on a normal set-up the potential for a downstream short is limited - but there may be other people in addition to myself whose brain has gone into hibernation - on the other hand, no protection would generate additional sales
Combined with a built in thermal overload protection, the MC33887 should be well protected from any kind of abuse such as short circuits and other overloads. In all practical terms, the MC33887 should be "destruction proof".
 

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Soren Winkler Rasmussen
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355 Posts
Discussion Starter · #29 ·
Hi Richard

QUOTE (RichG @ 1 May 2005, 12:09)Have you, or anyone else, enthusiasm for a SSD compatible mode for CarDCC.I think it's a good idea.

I haven't given it a lot of thought, because I don't know very much about the SSD dataformat.

I agree though, that the only difference would be software. We're planning to build a software download facility into the CarDCC track controller. This could also be used to load new functionality into both track controller and car controller.
QUOTE Alternatively the CarDCC car controllers could be used with the existing SSD Powerbase with the benefit of better performance and control.That should not be a problem seen from the hardware point of view. You'd only need to adopt the SSD protocol and add the transmission of the IR-LED identification sequence.
QUOTE What do you think, could be a best of both worlds way forward?It certainly could.

I'm currently working on the CarDCC protocol, but a SSD compatibility mode would be a nice feature to add. It should be possible to make software versions for both CarDCC, SSD and Pro-X compatibility. That way every user has full flexibility from the same hardware.
QUOTE On the cct is the PWM signal for the rear lights generated in the microcontroller, and then brake from the motor driver?Correct, but the the motor driver brake signal is generated in the microcontroller and fed to the motor through the motor driver.

The only motor PWM signal that is automatically generated in the motor driver hardware, is the automatic overload protection system. It has priority over the PWM controls from the microcontroller.
QUOTE I realise you can add a lighting controller to the car if more inputs and outputs are needed but I feel that more inputs / outputs in the base controller would be of benefit.I agree.


With the current design I have tried to balance functionality, size and cost. As the Signal Controller (former Light Controller) is really small (6x34mm), and will easily fit into a car, I thought it was an acceptable compromise. You can also add more than one car controller to a car.

The current car controller has two light control outputs that can be used for various control functions such as brake lights, rear/brake lights, exhaust flames, glowing brake discs and safetycar flash lights.

The downside of adding more outputs are:
-The size of the car controller will be bigger than 15x22mm, and difficult to fit inside an F1 car.
-All the cars that don't need more than two light control functions, will be unneccesarily expensive because of added functionality they're not using.

Extreme example (slight exaggeration ahead) ... You have 20 ordinary cars and a Coca-cola truck
:
It would be cheaper to put a lot of light controllers in the truck, and keep the cost of the ordinary cars down.
 

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Soren Winkler Rasmussen
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Discussion Starter · #30 ·
Hi Gord
QUOTE (Newbie1/32 @ 2 May 2005, 10:48)One idea, if possible, would be having the option to wire the l/c's on there own circuit.Yes, its possible.

You will need an extra track controller, and then you'll need to wire the LC's separately instead of connecting tham to the track.
QUOTE Best of luck with your project
Thank you very much.
 

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Soren Winkler Rasmussen
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Discussion Starter · #32 ·
Hi Gord
QUOTE (Newbie1/32 @ 6 May 2005, 19:18)Sounds like you have thought about darn near everything to make a truely all around system
Thank you

QUOTE How is your prototype coming along?I'm currently working on the Track Controller. The CC seems to be ok, but I can't know for sure until I have the TC up and running. I'm starting out with a very basic system that will only allow you to control car speed and download new software. The plan is then to release a steady flow of software for download as new features are added.
QUOTE May I pry and ask when it will be available,and will it be more affordable to the general public than Davic?I can't really say for sure, but I'm hoping to have the basic system running before the summer holidays. The reason I can't be more specific is that there are many unknowns: how many problems will I meet?, how much spare time will I have?, will I have to redesign parts of the system?.

I'll keep you posted though when I'm closer to having a working system.

I've made a preliminary calculation of the component prices here ... look for the BOM.xls attachment to my post on 05.05.2005.
 
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