Building a 6ch steering wheel Tx....

[clockworks]

I've been racing 1/10 B4 buggy and a 1/12 Mardave carpet racer for a couple of years using a KP Mars steering wheel Tx. I recently got my first crawler - a Venom Creeper. Since my existing Tx only has 3 channels, I decided to get a DX6i, which I converted to 2-axis.

I've tried racing my B4 using the Spektrum, but I was rubbish with sticks.
So, I've decided to try and combine this


and this


A quick look inside both Txs confirms that all the bits should fit, but I'll have to make an extension to the rear of the wheel Tx to hold the DX6i's main PCB and display. The scroll wheel will fit in place of the small LCD display. The toggle switches will replace the pushbuttons on the Mars.

First job was to see if it would work - whether I'd have full control over the steering and throttle. The potentiometers in the 2 Txs are physically different and have slightly different resistances - 5K in the Spekky, 4.5K in the KO.

I decided to join the 2 together with a couple of lengths of stereo interconnect


After binding the resulting lash-up to my Venom, the steering was a bit off centre. Some fiddling in the menus (subtrim and travel) had the steering working properly. I re-calibrated the ESC, and the throttle works, too.
Tried the same with my B4, and that seems OK as well.

Next step is to make the interconnecting cables secure and take the mega-Tx to the track for some proper testing.
Once I know it works in practice, I'll gut the KO and start on the casework mods.
Watch this space!

[clockworks]

Just been for a thrash round the back yard with the B4. Steering is fine, as is forward throttle. Almost complete lack of brakes, though.
Using my old 40MHz radio and the Losi Xcelorin brushless set up for 50% brakes, I can lock the wheels easily by hitting the brakes.
With the hybrid Tx, hitting full brakes is more like using drag brakes - just gentle retardation, no hint of wheel locking.
I've tried altering the trims and throws on the Tx and re-calibrating the ESC each time, but I can't get the brakes to work properly.

I think that the problem is with the throttle pot in the Mars. There's very little trigger travel in the "reverse" direction, so the resistance of the pot doesn't change much between neutral and full reverse. I'm guessing that the KO's electronics compensate for this, sending out a "full reverse" signal at what is, in reality, probably only a 1/3 reverse input from the pot.

The DX6i has a full travel throttle pot, so the electronics are sending a signal that's proportional to the pot input. Supply it with the "1/3 reverse" input from the KO pot, and it just sends a 1/3 signal to the Rx.
It's enough for the ESC to calibrate, but not enough for it to actually apply full brakes.

I can't think of a solution to this problem

[Ripperfi]

Wow. I can not help you but am impressed by your will to try something different. I wish you good luck and hope one of the electronic minds on here can help you with your dilemma.

[toy4crawlin]

LOL haha I knew you were going to beat me to it.

That KO looks really good and all the buttons really help.

I'll be doing a build thread for DX6 to pistol soon too !
This will be cool as we can share info, but it looks like you have a good lead and some great knowledge on radio's

Very cool let's do it, except you first so I know what to look out for LOL :-P


Dont forget the PICS ! :-P

[ohmyCLOD!]

Originally Posted by clockworks

The DX6i has a full travel throttle pot, so the electronics are sending a signal that's proportional to the pot input. Supply it with the "1/3 reverse" input from the KO pot, and it just sends a 1/3 signal to the Rx.
It's enough for the ESC to calibrate, but not enough for it to actually apply full brakes.

I can't think of a solution to this problem

Can you replace the KO pot with a pot that would send proper resistance according to your throttle position. Just a thought... Good luck that is an awesome idea and mod

[toy4crawlin]

Originally Posted by ohmyCLOD!

.. Good luck that is an awesome idea and mod

Clockworks, pardon me for asking but I was wondering have you had this idea for a long time like I have ?
I'm glad you are, it is good timing as I have my new creations below nearly completed this would be the perfect next step.

"[QUOTE= toy4crawlin;]
Might be easier to fit the DX6i parts into an old FM steeringwheel Tx ...... actually, that's not a bad idea. I've got a spare KO Mars Tx that could be modified. While I've got my DX6i in pieces, I'll take some photos and some measurements. Could be an interesting project - a six channel wheel Tx for less than $150. " [QUOTE]

I have wanting to do since last year when I got my DX6 .

[Aussie Nerd]

I would try and replace the 4.5k in the mars with some 5k of the same size That would be your problem most likely.

Kieren

[clockworks]

Originally Posted by ohmyCLOD!

Can you replace the KO pot with a pot that would send proper resistance according to your throttle position. Just a thought... Good luck that is an awesome idea and mod

If I could find a suitable pot, that would certainly solve the problem - I don't think that such a thing exists, though.

Measuring it with a meter, the pot is 4.5K ohm across the 2 outer pins. This is the resistance of the full length of the track. The pot has a total rotation of around 60 degrees.
When fitted in the KO, the pot is centred when the trigger is at neutral, so the resistance between the wiper and each end of the track is 2.25K.

Moving the trigger to full forward, the wiper moves close to one end of the track - the resistance increases to 3.75K (measured to the ground track terminal).

Moving the trigger to full reverse, the shaft rotates through a smaller angle, so the wiper moves less - the resistance drops to 1.82K.

The problem, as I see it, is that the change from neutral to forward is 1.5K, the change from neutral to reverse is just 0.43K - around 1/3. Since the pot is, presumably, used as a potential divider, this gives me 50% voltage at neutral, 83% at forward and 40% at reverse.
Whatever value linear pot I fit, the percentage change would be the same. I'd need a custom pot with a specific track - 30 degrees of linear track one way, 10 degrees of "thinner" linear track the other way.

There's probably a way of simulating this electronically, but it's beyond my knowledge.

[clockworks]

Originally Posted by Aussie Nerd

I would try and replace the 4.5k in the mars with some 5k of the same size That would be your problem most likely.

Kieren

AFAIK, the pots are used as potential dividers. Whatever the resistance of the pot (within reason), the voltage at the wiper would be the same for any given angle of rotation.

[clockworks]

[QUOTE=toy4crawlin;1850154]Clockworks, pardon me for asking but I was wondering have you had this idea for a long time like I have ?
I'm glad you are, it is good timing as I have my new creations below nearly completed this would be the perfect next step.

"[QUOTE= toy4crawlin;]
Might be easier to fit the DX6i parts into an old FM steeringwheel Tx ...... actually, that's not a bad idea. I've got a spare KO Mars Tx that could be modified. While I've got my DX6i in pieces, I'll take some photos and some measurements. Could be an interesting project - a six channel wheel Tx for less than $150. "

I have wanting to do since last year when I got my DX6 .

No, I haven't been thinking about this for long - I "stole" your idea from the other thread

[toy4crawlin]

No, I haven't been thinking about this for long - I "stole" your idea from the other thread [/QUOTE]

lol , well it was probably a distant thought after you drove your crawler.

Any how I think the radio you have for this project is the best suitable one.
I like the Airtronics XL2P, have 2 of them but I might try using my broken Futaba junior or the flight stick
I'll stop robbing your thread so it's not filled up with gobably.

Looking forward to pics of progress

[clockworks]

Before I set off for work this morning, I was thinking about this reverse throttle problem. I went up in the loft and found my old TQ3 E-Maxx Tx. I noticed that the throttle trigger moved an equal amount in forwards and reverse, unlike my KO.
I got home from work and took a number 11 xacto blade to the trigger, cutting off the lug that limits travel in the reverse direction. I also cut a slot in the case to allow the bit you push forwards to move inside the case slightly.
I now have 25 degrees of movement when the trigger is pulled, 20 degrees when it is pushed.

I re-calibrated the ESC and took the B4 into the back yard - success! The brakes now work fine, but moving into reverse is a little fierce. Hopefully some tweaking of the brake curve and Tx settings will fix this.

[toy4crawlin]

Great thinking, are you still going for doing the 6ch pistol

[clockworks]

Yes, I'm going for it.
I've stripped the KO Tx and ordered the parts I need - switches, pots and knobs.

[toy4crawlin]

cool,

why not use the pots from the DX ? is it easier to fit different ones or something ?

I opened up my DX6 last night and all the pots are the same and mounted on little circuit boards 1/4 x 1" how about yours

What does your LCD circuit board look like ? mine is 4" tall shaped like a " T " so I think it won't fit in a regular pistol radio.


Post some pics of the GUTS

[clockworks]

The KO Tx is stripped out. I've modified the trigger mechanism and cut away some of the main casings to give me more throw in both directions. On the DX6i "monitor" screen I'm now getting about 85% throw each way. The standard sticks move the pointer 2 segments on the screen, the modified KO trigger and steering both move the pointer almost 1.75 segments.
Before the mods, forward movement was 1.25 segments, reverse/brake was about 0.75. Both measurements taken with the "aileron" travel set to 125%.

As the trigger now moves up inside the top housing on full brake, I've also carved away part of the rear case so that my trigger finger sits comfortably.

Pics of the gutted KO:


I've also realised that I'll need to add pots or switches to the rudder and elevator channels so that I can calibrate them.
I'll fit a 3-way switch for the rudder channel (which is used for the rear steering) and a pot and knob for the elevator channel (for future use).
Along with the crab/2ws/4ws mix switch and the 2 diff lock switches, these will all fit in the 6-hole panel in front of the trigger, on a carbon fibre or alloy plate.

The scroll wheel will go in the space to the left of the wheel.

The silver switch behind the trigger will be the trainer/bind switch.

The silver slide switch in front of the trigger will be the power switch.

The base currently holds an 8AA 2x2x2 battery box. I'll fit a 2x2 box instead.

[Aussie Nerd]

Hi t4c As far as I know the dx6i does not have a voltage reg as it only hads 4 batts. That might be another reason for you to buy a dx6i

Kieren

[clockworks]

I've just bought another DX6i, secondhand on eBay. As soon as I've received and tested it, I'll completely dismantle one of them and post pics of all the parts.

T4C:
If your display PCB is 4" tall, it won't fit inside the Mars. The "head" of the Mars is 6" x 2.25" inside. Not sure yet if the DX6i main board will fit without extending the case.
Looking at the pics on your conversion thread, the Magnum Tx seems to be a similar size to my KO Mars.

It's my intention to have the display on the back face of the Mars. From what I can see (without dismantling it), the DX6i display board is linked to the main board with a flat mylar ribbon - there's no way I'm trying to extend that! The idea is to remove the square housing on the back of the Mars (originally held the FM module), fit the display through the resulting hole with a new acrylic screen, then fit the main PCB inside the rear case.
Everything else will fit to the front case.

If I need to extend the rear case to get the boards to fit, I'll make the extensions with 2mm Plasticard (Evergreen styrene sheet). This is real easy to work with.

The DX6i pots are physically larger than than the KO pots, so they won't fit. Even if they did, there'd be no advantage. They are both 60 degree pots, so I'd still have the same movement/throw issues.

[toy4crawlin]

ok thanks Clokwrks for checking and verifying that.

wow , how come you bought another DX ?
how much? I see many of them being sold without receiver
Is the DX6i and newer model ?
Maybe I will sell my D6 and get the 6i, I found a mars for $15.
My LCD also has the flat ribbon wire.
Any experience making plastic molds ?

thanks again and keep up the good work

[clockworks]

I bought another one so that I've got a spare if I break the first one. I'll also be able to carry on using a Tx while I'm doing the conversion - I reckon I'll be working on it for a couple of weeks.
Once (if) I've got everything working, I can sell the original one on eBay. Should get most of my money back. Might keep the receiver and just sell the Tx.

I paid 102GBP ($165). Best UK price on a new DX6i is 130GBP ($215). Those prices are for the complete kit with the AR6200 twin receiver. It's never been used, only a few weeks old.

DX6i is the replacement model for the DX6. If you can get a good price for your DX6, it might be worth buying a DX6i to mod, then selling your DX6 when you've completed the conversion.
My plan is to make no permanent changes to the DX6i, just unsolder the wires and transplant the electronics into the new case. If it doesn't work out, I can simply put the DX6i back together and sell it.

If you can get a Mars for $15, go for it. When I bought mine, it was KO's top of the range Tx. Cost me well over 200GBP. KO was regarded as the top surface radio manufacturer here in the UK when FM was king. Many racers still use the KO Vantage, the stick equivalent. For some reason, stick is more popular with racers here.

I've never tried moulding plastic. Anything I need to build will be made from flat styrene sheet, cut, shaped and glued together. Any curved shapes can be carved from a solid block, made by laminating several sheets together.
I use "Polyweld" MEK solvent to stick the pieces together. It melts the plastic, fusing it seamlessly.