Spektrum DX3 CH3 Mod

[BrianG]

Ever notice that the CH3 buttons on the Spektrum DX3 radio are momentary? If using for shifting gears in your transmission, you have to hold it in place. Also, the switch (labeled "A" on the radio) is kinda clunky to reach.

Well, I thought I'd add another switch so it wouldn't have to be manually held in place. This switch will be in parallel to the existing CH3 switch, so if you still want the momentary effect, it will still work - just put the new switch in the center position.

This is the switch I used. It has to be a SPDT (single pole, double throw) "center-off" type. "Center-off" means that the center position is totally "off", and either up or down is "on".

The existing CH3 switch is actually two switches with one common leg. You have to solder the center pin of the new switch to the solder point marked as "2" in one of the pcitures below. Then, the other two connections of the new switch can be soldered to solder points 1 and 3. Then, hook a servo up and try it. If it's backwards, just swap the wires on solder pads 1 and 3.

To use this feature, CH3 must be set to the "3P" (3 position) mode.

The switch needs a 1/4" hole to mount. I installed it so it could be easily switched using my trigger hand thumb.

[crazyjr]

Very nice BrianG, I never mess with the third channel. Too many bad optidrives.

[jhautz]

Excellent Work! That fixes one of the biggest drawbacks of that radio.

[BrianG]

Thanks guys!

@crazyjr: Yeah, the Optidrive is a nice idea in theory, but is prone to fail. All it is really is a reverse-lockout while the vehicle is moving. It can be removed as long as the user knows to wait until the truck fully stops before engaging reverse. Besides, the reverse gears and mechanism are really weak anyway.

@jhautz: I thought so too. I remember when I made by first BL Revo, I was going to use the shifting feature in the emaxx tranny, but decided that shifting it would be too much a PITA. So I didn't use it.

I don't know if I will ever use the third channel, but at least it is usable now.

Really, you could replace the existing switch with a toggle, but the little circuit board in my pics would have to be cut to allow clearance. Even then, you would no longer have the momentary effect if you decided you wanted it. And, if CH3 was set to either of the other two modes ("0" and "LN"), it wouldn't work right.

By the way, I tested to see what would happen if the toggle was switched one way and the existing one switched the other and nothing bad happens. So, there seems to be no danger whatsoever. The only gotcha in this mod is the placement of the switch; too high and it interferes with the circuit board - too low and it interferes with your thumb. :)

[JB3231]

Which button controls the third channel? I have the DX3 and never looked for it.

[BrianG]

Originally Posted by JB3231

Which button controls the third channel? I have the DX3 and never looked for it.

The "A" button, which is the one furthest back and up of the two...

[coolhandcountry]

Cool. It sounds promising.

[neweuser]

Great Solder job man! How did you get it so small???

[BrianG]

I'm an old hand at soldering. :)

What do you mean by "How did you get it so small???"

[coolhandcountry]

I would guess the solder joint.

[BrianG]

Hmm, I guess the answer would be "practice" then. :)

[jollyjumper]

on my graupner radio (jr in usa) the 3rd channel was like the spektrum's button.
but it did stay put in gear when you shifted, just have set it on 2p in the settings on the radio.
then it moved if you pushed the button from gear 1 to 2 and if you pressed it again it shifted down.

[BrianG]

Well, even though the Spektum is based off an older JR radio, CH3 does not have this feature in the DX3. Even in the manual it states that you have to hold the button for shifting. In the newer DX3.0, there is an option for momentary vs toggle.

[jollyjumper]

oh i see.