6ch Pistol Tx - a cheap alternative?

[clockworks]

Having completed my DX6i pistol Tx, I've been thinking about a cheaper alternative, prompted by responses to my other build thread, specifically from forum member edwalsh18.

The DX6i is probably more than most people need in a Tx. Selectable proportional 4ws seems to be the main requirement - everything else can be done with a 3-position switch. It's also expensive - my DX6i build cost me about $400.

It's been pointed out to me that you can get a Chinese brand 2.4GHz non-computer stick Tx and Rx for around $30. Obviously you don't get model memories, adjustable end points or mixing, just a basic Tx, but I think it could be modified for selectable 4ws.

My idea is to replace the single steering pot in the donor pistol Tx with a dual concentric pot to control 2 channels from the one steering wheel - probably channels 1 and 4. This would allow both the front and rear servos to be controlled by the wheel.

By using switches, the positive and ground inputs to the rear pot could be reversed, allowing the choice of normal 4ws or crab. The rear steering could also be "locked out" by bypassing the pot with a switch and a couple of resistors. The same could be done with the front steering.
You'd end up with 2 switches. One would select front/both/rear, the other would select normal 4ws/crab.

It would also be necessary to add EPA pots to both the steering channels (or use programmable digital servos) - this is explained in fritobandito's TQ3 sticky.

The only thing that's got me stumped is finding a suitable pot. It needs to be a dual linear, close to 5K. Most dual pots are log taper, and much higher resistance.

Is anyone interested in pursuing this idea? I reckon the total build cost should be less than $100.

[edwalsh18]

i knew it could be done! now that beats my idea of having a TQ3 with a stick 2.4ghz implant and 2 TQ3 steering wheels! LMAO! i should be getting my DX6i... oops i mean my HDX6i in a few days it was $30 shipped. then we can see if this idea works with my TQ3

http://www.rcgroups.com/forums/attac...mentid=2653257

[mrklaw]

why do you need a concentric dual pot? Can't you use two normal pots on a common axle?

Like this idea a lot - would you also have a set of 2/3-pos switches for winches, lights, digs etc?

[clockworks]

Originally Posted by mrklaw

why do you need a concentric dual pot? Can't you use two normal pots on a common axle?

Like this idea a lot - would you also have a set of 2/3-pos switches for winches, lights, digs etc?

I suppose that you could modify 2 normal pots, but a dual-gang pot is a lot simpler. That's what I meant to say in the first post - dual-gang (2 pots sharing a common spindle) rather than dual concentric (2 pots on a common axis, but with 2 separate controls).

I've found a UK supplier (Maplin) of a suitable 4K7 linear pot, so no problem there, as long as it physically fits the donor case. I looks like it's a 1" diameter standard pot, rather than the 5/8" miniature size that's commonly used in Txs.
The best miniature dual linear pot I can find is 10K - should still work OK.

My thinking is to use 3 channels (1 2 and 4) for steering and ESC. This would leave one proportional channel free (ch 3), which could be used as a 3-position. Channels 5 and 6 would be 2-position.

[clockworks]

Originally Posted by edwalsh18

i knew it could be done! now that beats my idea of having a TQ3 with a stick 2.4ghz implant and 2 TQ3 steering wheels! LMAO! i should be getting my DX6i... oops i mean my HDX6i in a few days it was $30 shipped. then we can see if this idea works with my TQ3

http://www.rcgroups.com/forums/attac...mentid=2653257

As soon as you get it, post some pics of the inside. We only really need to use the main circuit board and maybe the switches - put a ruler in the pics so we can see what size the components are.
Also, if you've got a multimeter, disconnect one of the pots and measure the resistance between the 2 outside terminals, so we know what size pots are needed for the conversion.

[mrklaw]

would it be possible to have the rear steer controllable directly from a momentary 3-way switch as well, so you can choose to either have it proportional with the front, or independent?

[clockworks]

Originally Posted by mrklaw

would it be possible to have the rear steer controllable directly from a momentary 3-way switch as well, so you can choose to either have it proportional with the front, or independent?

I don't see why not. If the basic conversion works, you could wire it up any way you like. Just means adding extra switches and resistors.

[clockworks]

I found an unused Turborix 2.4GHz 6ch PC-programmable Tx and Rx on eBay for 25GBP plus postage (just over $50 total) so I bought it. Now looking for a cheap pistol Tx to use as the base for the conversion.

Total budget for the build is $100 - I wonder if it can be done?

The plan is to add fully-selectable 4WS (front only, rear only, 4WS and crab), all controlled by the steering wheel and 1 or 2 switches.
Also want to add a 3-position switch, a 3-position momentary switch (for a winch) and a 2-position switch.

If anyone's got any other stuff that would be good to add, post your ideas and I'll try and figure out how to make them work.

[mrklaw]

what are your main criteria for the pistol? Just lots of room inside or will you need some of the electronics?

[clockworks]

Originally Posted by mrklaw

what are your main criteria for the pistol? Just lots of room inside or will you need some of the electronics?

I want something that sits well in the hand and doesn't look cheap! I've got a Traxxas TQ3 and a Losi 27MHz Tx, but they are both quite nasty to hold.

Next up is room for the main PCB and switches - until I receive the Turborix Tx, I don't know how much room I'll need. If I can do this conversion without too much styrene work, it'll be a lot easier for anyone who wants to copy it. With my last conversion, rebuilding the case was the hardest part.
I'm planning on replacing the wheel pot with a dual-gang pot, so there needs to be room inside for that.

I don't need any of the electronics, just the wheel and trigger mechanisms, the trigger pot, the battery holder and any switches which can be re-used.

I'm thinking that maybe an old Futaba AM Tx will do the job.

[clockworks]

Oops - just realised that the Turborix Tx has programmable mixing, so I won't need a dual pot for the steering, just a couple of switches and some resistors.

[ScalerLover]

Heres a link to that turborix transmitter if theres no more on ebay

http://r2hobbies.com/proddetail.php?...cps61206_61411

EDIT, theres someone else thats already done the conversion with that tx and is asking 150.00 shipped to the US so i think your price goal is good.

[clockworks]

Originally Posted by ScalerLover

EDIT, theres someone else thats already done the conversion with that tx and is asking 150.00 shipped to the US so i think your price goal is good.

Do you have a link? - interested to see what they've done.

[ScalerLover]

Here you go.
6 Channel pistol grip 2,4Ghz

[clockworks]

Thanks - I saw that thread, but didn't realise that he was selling them.

[ScalerLover]

Well technically hes not selling them on the forum, i just pmed him and asked what it would cost if he were to do so.

[mrklaw]

I think its ok to sell them. i'd love a 6ch pistol but couldn't make one. Have enough trouble understanding the basic wiring on the car, and the mechanicals..

Btw, if you had one switch for front/rear/both, then don't you just need a 2-way for the direction that the rears shouls go?

I.e. Follow the fronts=crab or opposite=4ws. You don't need a 'normal' as that would be achieved with the first switch set to front steer only

so the first switch has front or rear =directly controlled by the wheel. 'both' steers both and uses switch 2 to choose how?

So then with just two switches you have selectable 2ws, 4ws, crab and independant rear steer

(you could go all out and have a 4 position rotary dial which would cover all options in one switch - 1)front steer; 2)4ws; 3)crab; 4)rear steer)

[clockworks]

Using a 4-position rotary switch is my plan.
I'll check that everything works using toggle switches first, since I already have those. The actual switch layout can be whatever you want. The problem with a "front/rear/both" toggle switch is that most 3-position switches are "off" in the middle position. I've got a couple of on-on-on switches, but they do really weird stuff like having one pole on at one end, both poles on in the middle, and the other pole on at the other end - not really what I need.
I need to sit down and think about this.

A 3 pole 4-position rotary is probably the best solution.

I'll make sure that the Turborix Tx and Rx work, then start the mods.

[clockworks]

The Turborix Tx and Rx work OK, but a few points:

The Tx needs a decent set of batteries. Fresh "budget" alkaline cells showed as nearly flat. Worked for about 10 minutes. NiMH cells seem OK.

The Tx has mechanical trims that rotate the main pots in the gimbals, rather than electronic digital trims. I guess that all budget Txs use the same method? I'll have to use trimpots to allow trimming "on the fly" for the steering channels.

The main PCB is a bit bigger than I anticipated - slightly over 6" wide - so I'll need to use a fairly large pistolgrip Tx to avoid extensive styrene work.

The Tx has 3 programmable mixes, but channels 5 and 6 need a mix each - there are no hard-wired switches for these channels.
If I want to use 2 mixes for 4WS, I'll only have 2 spare channels to convert to 2- or 3-position switches.

Without connecting a PC, there is no facility to store more than one model. Although it's advertised as having 4 model memories, that seems to be a bad translation from Chinese. It actually has 4 model TYPES - plane and 3 types of helicopter. Switching between these model types needs a PC, and just alters the mix/switch profiles that are available.


Positives:
EPA and sub-trims work on all 6 channels.
Relatively simple design means less wiring than with a proper computer radio.
The pots appear to be standard 5K linear, like branded Txs.
It's very cheap - complete setup costs less than Spektrum's cheapest Rx.

[nosduj]

sounds promising. Subscribed