SlotForum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
3,748 Posts
Discussion Starter · #1 ·
I've had an SCX Rally Chrono for a few months now and while liking it generally the fact that the sensor sometimes misses cars (including SCX ones) and doesn't work at all with some other cars wasn't good.
So I had a look at how the sensor works, all it does is short the two wires that go into the 3.5mm jack plug on the base unit, I found this out using a multimeter and passing a car over the sensor.
I had a think about how I could short out these two wires as a car went past, I considered using a dead track but was worried that the back EMF might damage the electronics inside the base unit, instead of this I used an old Scalextric lap timer, the type with two dials, I took the dials off and one lanes actuating arm out. On the other actuating arm I have attached an old Matchbox LaneChanger car pickup shoe, and on the base I have attached an old braid, both have wires connected to them which are connected to a jack plug, as the car goes through the lap timer the actuating arm moves and the pickup makes a connection with the braid, shorting out the two wires, triggering the Rally Chrono.
This now means that so long as the guide is in the slot the car will trigger the Chrono, I've tested it with SCX, Revell and Ninco cars and it works fine, the old style Carrera guide skips over the top of it.

Next step is to reduce the travel and spring pressure of the actuating arm.

No parts of the Rally Chrono were harmed in the making of this sensor.
 

·
Premium Member
Joined
·
4,213 Posts
Interesting - any pics?

I was wondering if a switch like this could be used instead?



Mounted under the track and pressed down as the guide passes over the top? - perhaps the sping preasure would be too much?

Perhaps this might be better?

 

·
Registered
Joined
·
3,748 Posts
I'll do some pics (and post your 205) shortly, it looks a bit Heath Robinson though and needs a serious tidy up and finish.
I considered switchs like those, but thought they might de slot the car and would also need the track to be raised. You'd also have to find a switch that fitted between the rails without shorting the rails to each other.
My solution also had the added bonus of costing me nothing as I had all the bits, I think it took me around 30 minutes to do as well (which is why it needs tidying)
 

·
fred
Joined
·
1,608 Posts
I am so glad about this.

I was getting more and more axious as I reading the thread, but by now knowing the rally chronos is totally unharmed in the making of what is likely to be a very botched sensor, I can sleep easy.
 

·
Registered
Joined
·
3,748 Posts
Discussion Starter · #5 ·
You wish you could achieve the high level of craftsmanship of a appenticeship trained engineer

And yes it is held together with duct tape.
 

·
fred
Joined
·
1,608 Posts
Ah yes julian, I defer to you.

I know my modelling and construction skills are limited made more so by always sticking my fingers together or to plastic or tissue paper
 

·
Registered
Joined
·
3,748 Posts
Discussion Starter · #7 ·
I usually end up with mine stuck to the windows of the slot car, just where you can't rub it down and start again.
And my apprenticeship was in electronics, so while the stuff I make works, it's not exactly attractive. I'm thinking of a building over the top of the old lap counter to make it look nice.
Anyway Scudbong makes them, I scrape them (his lovely little Lotus springs to mind
)
 

·
Registered
Joined
·
3,748 Posts
Discussion Starter · #8 ·
I took some pictures with my phone yesterday but they're a bit blurry now I've got them on the computer.
Anyway, I've tidied it up now, connectors and other bits epoxied in place and the wires now run under the track inside the old lapcounter.
It works really well, hasn't missed a lap so far.
 

·
Registered
Joined
·
377 Posts
scx use a magnetic reed switch.

you can back an opto switch ( photo electric switch) for a couple of pounds! I know Pendle have done that as we have very simple! or you could use a dead strip even cheaper to make!!

nic
 

·
Registered
Joined
·
2,555 Posts
I's also be interested to see how you've done this mod. A chrono is the next track item on my wish list.
 

·
Registered
Joined
·
3,748 Posts
Discussion Starter · #11 ·
Optical sensors are okay, but every track I've been to with them has had minor problems with them at some point, dead strips work well but I had a couple of concerns with using this with the Chrono, 1st would the cars be going over it fast enough not to stop and 2nd would the back emf from a direct dead strip cause damage, you could easily use a relay to solve this, but this would involve extra cost.

Using the old lap counter was really easy, as the car goes through it there's an arm that slides into the lap counter, normally this arm works the lap counter dial, all you need to do is put an electrical contact on this arm and another on the case, then set them up so that when the arm is in the contacts make, and when the arm is out the contact breaks. If you take apart an old lap counter you'll see what I mean.
 

·
Registered
Joined
·
2,555 Posts
As my collection of cars expands and diversifies, I'm getting more and more cars that won't trip the switch on the chrono. Fly Porsche 911, Revell Ascona and Spirit 205T16 are the main offenders currently, but I have another 3 cars coming soon (2x MSC and another Fly) that could compound the issue. Sorry, I'm waffling.
Anyway..........

My solution to the problem also used some classic Scalextric parts:-
1x battery operated lap counter/timer (the C8045, I think it is)
1x broken controller

The only other thing I used was a screw connector block.

I opened-up the lapcounter and cut the wires from the lane 2 switch (which is only 2 pieces of springy metal pushed together by a plastic rocker activated by the guide blade of the car) right up close to the PCB. Then I cut the jack plug off the controller - it's the early, non-brakes, two-wire type. The switch wires were connected to the jack plug with the screw connector - this sits nicely in the lap counter switch/PCB/LED housing (you could solder the cables together, but my soldering skills are still not that good). I needed to cut a slot in the housing for the cable to come out of, but the lap counter is now not fit for its intended purpose, so it's no big deal. While I had the lap counter apart, I removed the plastic rocker from the other lane. The jack plug now goes in place of the original Chrono one, which I have left connected to its track - just in case.

I've fitted the track piece immediately before the Chrono "junction", but it could now go anywhere in the layout, by extending the cable as necessary.

If I ever get 'round to it, I'll cut the lap counter switch/PCB/LED housing off the track and replace it with a Sport half straight border, just to tidy things a bit. But, as with everything else, no-one but me is ever likely to see it so it may never happen.
 

·
Registered
Joined
·
14 Posts
Hi,
I have replaced the reed switch on the SCX unit with a lever activated micro switch. Both on our club rally track (Quorn Slot Car Club) and also on my home double ended routed rally track(single lane - loop each end - with a bit of electronics to change the polarity) all works 100%

Cheerrs,

Andrew
 
1 - 13 of 13 Posts
Top