MITTENTITEL
All the values given are measured and can differ between systems.
 

 

At the first look you might mistake the SCX controllers for ordinary gun controllers, but a lokk at the pcb tells different.

Instead of a potentiometer it uses a resistor chain and instead of aeparate outputs for throttle and switch it uses a multiplexed output.

The black wire is connected to ground.
The yellow wire is the output.
When red is conencted to a positive voltage the switch is driving the output signal.
Gree is the inverted signal to red, so it has a positive voltage when the throttle shall drive the output line.

The red wires and the green wires of all controllers are connected. This hints to the fact that all controllers are read at the same time.

Most interstingley the frequencies with which the controllers a read differ between the terminals.

Terminal High Level
Red/Green		 Samples per second Red High/Green Low
Read switch		 Red Low/Green High
Read throtle
Standard
5V
62,5
8 ms
8 ms
Pit stop
3,35V
20,3
30,8 ms
18,4 ms

It's easy to see that each controller is sampled more than once during a phase. That means that changes to the throttle while the throttle phase is active are registered nearly without ay delay, but when in a switch phase a throttle change goes completely unnotived. Accordingly are switch presses and releases registered quickly during switch phases and not at all during throttle phases.

I find it absolutely suprising that SCX thinks that the lane change switch is so much more important than the throttle.

While the throttle is read 50% of the time with a standard terminal, its only 32% wit the pit stop terminal. And the absolute dead time is nearly 4 times as large as with the standard terminal.

The controllers give 10 speed levels including 0. The voltages differ for each terminal type as do the voltages indicating a press of the switch.

Terminal Taste
nicht gedrückt		 Taste
gedrückt		 0 1 2 3 4 5 6 7 8 9
Standard
1,9V
3,8V
0V
1,2V
1,52V
1,84V
2,32V
2,8V
3,28V
3,76V
4,24V
4,64V
Pit stop
1,3V
2,6V
0V
0,72V
0,92V
1,16V
1,32V
1,72V
2,02V
2,36V
2,72V
3,0V

Instead of using 0V and full voltage the use of two positive voltages for the two switch states allows for easy detection of unused controller ports.

Life is never easy and so the ten throttle settings do not map to the speed settings of 0 to 9.

The SCX protocol reserves 4 bits for the speed parameter. That's 16 (0-15) distinct speed levels. The highest (15) can't be generated by ordinary means. The cars react to speed levels 13 and 14, but they can not be generated with ordinary controllers. You could design a a special controller interface connected to the shuttle interface which makes these levels available. The value 15 can not be generated over the shuttle interface, because it uses 15 to signal an unused controller connector.

So theer are 13 levels left (0-12). But the controllers generate only 10 levels. The standard terminal does not generate the levels 2, 7 and 11. The pit stop terminal does not generate the levels 7, 9 and 11.

Alexander Bauer measured the available speed levels in dependency to fuel level. The table below shows the mapping from throttle setting to speed level at tdifferent fuel levels:

Fuel level
0
1
2
3
4
5
6
7
8
9
8 or 7
0
1
2
3
4
5
6
6
10
12
6 or 5
0
1
2
3
4
5
6
7
10
12

4 or 3
0
1
2
3
4
5
6
8
10
12
2 or 1
0
1
2
3
4
5
6
9
10
12
0
0
0
0
0
0
0
0
0
0
0

It's a bit weird that they go through all the hassle to make the mapping fuel level dependent and than only change one value which is not the top one. I will lokk into this once I find the time.

The cars handling might change a bit, but the lap times will most likely not suffer.


Whe using junior mode oly speed levels 0-8 are used. Throttle settings 7 and 8 result in the same speed level.

Even if you would replace the resistor chain with a potentiometer you would not gain a finer granularity. The terminals do only distinguish 10 levels for the throttle.