Technical Radio Question

[drummerboy827]

So basically what i'm trying to do is make full throttle on my controller make my boat go at any percentage i want. (ex. full throttle on controller = 50% full power on boat)

Now i wanted to know if this idea i had would work:
The idea was basically to hook a pot to the signal wire from the thumbstick and by changing the resistance, it would basically reduce the percentage of the signal sent to the boat.

Has anyone ever tried this? And if they did how many ohm pot did you use? Also, what is the signal voltage range on the stick, is backwards negative?

Thanks,
Chris

[wingnut163]

the radio has a pot in it, unless its a toy. then you need to change the electrionics.
(ex I'ntreapid sail boat, toy, i changed all and now i sail with a 2ch radio and sail and rudder control)

[drummerboy827]

I know the radio has a pot, but i'm talking about hooking a secondary one with a rotary knob to be able to scale the voltage from the radio pot.

In theory this seems to make sense, I was just wondering if anyone has any insite on things i may be missing

thanks again,
chris

[patmat2350]

No.
The pot in the radio is grounded on one end, and (usually) 5v on the other end. As you move the stick, you're adjusting the position of the center tap. On a regular pot, the center tap can go from one extreme to the other, getting a voltage of 0 to 5v. But on most radios, the mechanism doesn't go to the extremes, maybe the tap can see 1 to 4v (or less). Center stick will be about 2.5v though. This varying voltage is read by the radio, which then sends varying signals out to the Rx.
Changing the pot will do nothing. Substitute a 10k pot for the typical 5k, center will still be 2.5v.
Instead of dreaming up Rube Goldberg resistor arrays, it's best to get a radio that has end point adjustment on a channel that you can use for your ESC... that's exactly what the feature is designed for.
Pat Matthews

[green-boat]

Open the radio up and see what the Ohm rating on the pot is. It may be marked something like 2K,5K or 10K. If it is then buy another one with half of the original rating or close to it and the same size. The "K" rating is 1000 Ohms, so if it is marked 5K, then it is 5000 Ohms. To wire it in, unsolder the center wire going to the existing pot and resolder it to one of the outer leads of the new pot. Solder a new wire from the center lead of the new pot to the center lead of the old pot. Turning the new pot one way will allow the throttle to be as if nothing new had been done and turning it the other will give you the result you are looking for.

[Umi_Ryuzuki]

Seems to me that if you want to half speed at "full throttle" then I would just put a battery in the boat that is half the voltage.

:D :D :D

[patmat2350]

green-boat: This might have mixed results. The circuitry that reads the center tap is very high impedence- so very little current flows thru that lead. No current, no voltage drop across the added pot.
Then, if there is a volt drop, it'll be just like starting from an uncentered stick- sort of like a trim adjuster shifted to one side. Limits one direction, not the other!
PM

[drummerboy827]

I did some testing with a volt meter, and the pot that's already in there. There's 5 volts dc going into the pot. at full reverse the voltage is 2.5 volts, and at full throttle it's at 3.5. So adding a pot afterwards wont work to scale the voltage.

Heh, turns out the company who makes my radio (robbe) makes a board you can add to the controller to do exactly what i was trying to accomplish.

Thanks for the help,
Chris