Spektrum Throttle programming

A

AndySV1K

Member
Hi chaps,

I have a DX8 that i'm fiddling with, it uses 5k pots for the sticks, but it only uses a small amount of the travel, so for example 0-100% throttle will be something like 1.9k-3.8k (approx)
If I stick a 5k pot onto the board, it obviously doesnt allow me to use the full travel of the pot as it's looking to see that much narrower resistance range.

Now, is this something I can program out? i.e so that 5k = 100% throttle and 0 = 0% throttle?

I've tried playing with the throttle curve but it just changes how it behaves based on the same resistance range, it doesn't free up the pot to travel further.

Does anyone know the spektrum stuff well enough to help with this?

Andy.
 


A

AndySV1K

Member
Hi Ross,

Thanks for your reply,

I've messed around with throttle travel adjustment, but it doesn't seem to allow full travel of the pot still, it's still using the central 50-60% of travel I would say.

Andy.
 

Macsgrafs

Macsgrafs

Active Member
Hi Andy,

I'm sure you can take throttle limit up to 150% & down to -150%...have you tried that & what results did you get?

Ross
 


Macsgrafs

Macsgrafs

Active Member
To be honest with you Andy, I'm not sure that all pots give full value when used in the RC world!

Ross
 


RotorJockey

RotorJockey

Member
Hey Andy

Here's your solution - just up my alley!

You'll prob'ly have to juggle the values, but do this : Use a 1KOhm resistor on either side of a 3KOhm pot. The total value satisfies the 5KOhm requirement of the circuit, and the 3K (prob 2K7 Ohm) pot will give you full swing of it's travel. Get a bunch of 1KOhm half-watt resistors and a 3KOhm and a 4KOhm pot. Putting two 1Ks in parallel makes 500 Ohms; where connecting two in line (series) makes two K. You can do this on either side and use a 4K pot to alter the ratio of 'unused' swing of the pot. The ratio is straight numerical - (say) 2 x 1K in parallel = 500 Ohms + 3k pot + 2 x 1K in parallel = 500 Ohms + 1k in series still gives you 5K. By juggling the values, you 'skew' the position of the pot in the chain, which is exactly what you want! Enjoy basic electronics.
QED
 

RotorJockey

RotorJockey

Member
Radio controls are Voltage Dividers (In most cases!)

Further to our discussion Andy, the 'electronic' action of a variable resistor (potentiometer = pot) is to vary the level of input to a control circuit. This input could be a simple voltage, the level of a signal (e.g sound), the pulse-width of a square wave etc. The variable stuff comes off the CENTER pin of a pot.
If only a portion of the travel is used to satisfy the control function (say around the center), there is a 'fixed portion' of resistance on each side of the pot (between the center swing and the side pins).
In pure voltage terms (for control purposes), the supply voltage (say +5volts) is connected to the left pin ('top' of the pot), and the common (earth or negative) is connected to the right pin ('bottom' of the pot). The VARIABLE voltage is taken off the middle pin (connected to the slider). Measuring with a multi-meter between the middle and the bottom of the pot, the voltage will INCREASE with clockwise rotation, & vice-versa. Hence the resistance between the top and middle of the pot is REDUCING.
This function and circuit is called a VOLTAGE DIVIDER.
You can emulate this behavior (out of the box) by using a smaller value pot (to approximate the amount of the original pot used), and a fixed resistor on either end, the sum of the values MUST meet the value of the original pot, and the ratio between the values chosen to 'place' the pot in the right 'place' in the resistance chain. Now, the WHOLE travel (and value) of the new pot can be used to perform the desired function.
Sounds complex, but is actually quite simple!
 

You must log in or register to reply here.
Top