4ws with spektrum DX3

[mrklaw]

Hi

Finally got my parts for converting my Losi MRC to 4ws, and installed them tonight. It was my first chance to find out how the 4ws options worked on my spektrum DX3 (not 3.0). Even with lots of reading on the internet, I was still confused. I'd sort of expected to be able to have full left/right lock on the rear wheels by using the 'A' switch, but thats about it.

But it seems to offer quite a bit more, and I'd like to check I'm doing it right, and also if there is any way to go the final small step which is a bit of a pain.

I have the rear servo plugged into the standard Losi DSM receiver AUX channel. I have the DX3 set up to mix the steering 100% to channel 3, and I also have FN3 (ch3) set up to 3P mode (to enable the independent steer). now, for some reason the instructions say if I use mixing, I should set the FN3 mode to 0 (disabling the A button for rear steer). Is there any reason for this, or am I ok to keep it on.

Anyway, the result of this is better than I'd expected:

1) I have full time 4ws proportional with the front wheels
2) I have independent rear steer on the A button - full left/centre/right. This would be useful to bring the rear around when I don't want to move the front - just don't use the steerwheel.
3) I can change to crab mode by changing the direction of the channel 3 servo.

Now, a couple of questions.

To change to crab mode, I have to go into the menus. Its not too bad, it seems like you can just bring the page up (ch3 servo direction) and leave it there, and then switch between 4ws and crab by pressing the + and - buttons. But is there any way to get this more directly? eg on the B button, or somewhere else?

More importantly, is there any quick way to turn off the 4ws for when I just want front 2ws? Or do I have to dive into the menus and slowly (and loudly with the beeps) turn the mix down to 0%? Even if its only as quick as changing between 4ws/crab that'd be fine. If its not possible then I suppose the only alternative if front 2ws is important (it is I think), would be to ditch the mixing completely, and just drive the rears manually to acheive 'blunt' 4ws and crab? But it'd be a shame to lose that.

I'm pretty happy with it at the moment though

[clockworks]

I've had a quick read through the DX3 manual.

The reason why they tell you to disable ch3 (Fn3 0) is that steering mix on this Tx is designed for two servos mounted on the same axle, not separate front and rear steering. If you hit the "A" button, one servo would move, fighting the other one - not good.

When you are using the steering mix for 4ws, you want to be able to move the servos independently, so you're OK to leave ch3 in 3P mode.

I can't see an easy way of turning the mix on and off, or of reversing the mix.

I'd suggest trying to mod the Tx, but I don't think it has enough switches or options to do a successful mod. There's no direct control over channel 3, so it can't be done by adding switches or pots.
I had the same problem with my KO Mars - the third channel is only controllable through the software, so hardware mods aren't possible. That's what got me started on the whole Tx conversion business.

Unlike my Mars, your DX3 is still worth a fair amount - more than enough to pay for a 6ch Tx to modify. I'd sell it - I guess that's your plan for the future?

[mrklaw]

I wanted to test the 4ws first and then see what my options are. Also I use it with my firestorm flux and while I'd be happy to use a homebrew Tx with a slow crawler, I'm not sure about letting it loose on something doing 45mph!

I suppose I could transplant the Losi 2.4GHz into the firestorm though... then I'd have a DX3 and two SR300 receivers to sell on, which would help fund a custom crawler tx and a couple of receivers.

having a basic setup has helped me understand what I want from a 'proper' pistol crawler radio. Definitely like the independent rear steer - almost to the point where I'd disable the mixing completely and just drive with the A button and wheel. but proportionally mixed with the front is just too cool :P

So ultimately I will probably want a custom Tx for my crawlers (Losi MRC and CR01 being built now)

[clockworks]

Good point about finding out what your options are and what functions you actually need.

I use my DX6i modded Tx with my B4 buggy, which goes quite fast too. Works perfectly, just as well as my original 40FM Mars, with the added bonus of no frequency clashes or interference.
These 6ch Txs are designed for use with planes and helis, so reliability is probably more important than with a surface radio.
If the mods are done carefully, it'll be as reliable as the original it's based on.