As the working throttle voltage range is only 2V in total
(1.2 to 3.2V) I don't think diodes will give you many speed options.
I suggest you use resistors as shown below:
According to my calculations, this should give the following signal voltages and corresponding throttle percentages:
Switch Position Signal Voltage Throttle Percent Neutral 2.20V 0%
F1 2.42V 20% Forward
F2 2.62V 41% Forward
F3 2.83V 61% Forward
F4 3.03V 82% Forward
F5 3.24V 100% Forward
R1 1.85V 36% Reverse
R2 1.49V 73% Reverse
R3 1.12V 100% Reverse
The 200k trimpot (TP3) should be preset to give a resistance of approximately 103,000 Ohms between pins 1 & 2, and then readjusted when finally installed to read 2.20V between pins 1 & 2 with the rotary switch disconnected or held between 2 poles with contact open.
The 5k trimpots will need to be set as follows:
Preset TP1 to 3,150 Ohms between pins 1 & 2
(Pin 3 is not used)Preset TP2 to 2,800 Ohms between pins 1 & 2
(Pin 3 is not used)If necessary, readjust TP1 with the switch in the Neutral position until the Signal Voltage reads 2.20V relative to the Ground
(0V) Wire.
I'm not sure how much the 200k trimpot will affect the Throttle Signal Voltage when the rotary switch is operated, hopefully it won't make much difference and the throttle will work just as expected.
Check that you have a signal voltage of just over 3.2V with the switch in the F5 position, and just below 1.2V with the switch in the R3 position.
You may have to readjust TP1 and TP2 if the Signal Voltage is too low in the F5 position or too high in the R3 position whilst also ensuring that the Signal Voltage in Neutral is still ~2.2V.
Hopefully you'll be able to make it all work as hoped.
Alan 
Recent Posts