Repackaging a commercial Radio Control transmitter

[tramcar trev]

I want to do this with my 6 Channel Hobby King transmitter. I'll put it in a new plastic box with 5 knobs for speed control and one switch to turn smoke on and off. This allows for 1 knob for each of 5 trams which as I have discussed before will have manual reversing and auto directional headlights...

Problem; the potentiometers are 5K ohm linear ( that's what it says on the pots B5K0) but only the centre 60 degrees of the 300 degrees of "turn" are used and I want to replace the pots and be able to use the full sweep of 300 degrees.

Solution; As the pots are 5K over 300 degrees then divide the 5000 by 300 = 16.6 Ohms/degree of rotation. Ok so then as I have 60 degrees actually used there are 996 ohms in the swept area using the existing joystick. So if I use a 1K0 pot with a 2k0 fixed resistor on each "end" I end up close enough to 5K0 overall and the pot can be used for its full travel.

Can it be this simple? What am I missing here? If it is this easy then the only tricky bit will be desoldering and resoldering the coax for the antenna....

 

[nicebutdim]

Have you removed the pots from the transmitter and checked their travel? You 'may' find they only move by the amount the joystick does as I read online that the pots are specially designed for rc transmitters. If possible take out the pot after marking the end travels while the stick is still connected then measure the resistances using a multimeter. I'm after doing exactly the same as you, Trev, and this has become a sticky area for myself.

 

[Tony Walsham]

I'm doing four pots in a handheld plus a button working the 5th channel.

Mock up pic.

Missing ON - OFF button and Ch # 5/binding button.
Working prototype this week.

Sorry Kev, this uses Deltang DSM2 stuff and I am not at liberty to divulge pot or resistor values.
"Edit, added the following":
Feel free to poke around the Deltang website for circuit diagrams, but, be warned the resistor values used may not be compatible as the system is based on 3.1 volts. I am not sure what voltages the system uses in a stick radio. Some Hobby King TX's use 9.6 volts for the TX module.

 

[tramcar trev]

Have you removed the pots from the transmitter and checked their travel? You 'may' find they only move by the amount the joystick does as I read online that the pots are specially designed for rc transmitters. If possible take out the pot after marking the end travels while the stick is still connected then measure the resistances using a multimeter. I'm after doing exactly the same as you, Trev, and this has become a sticky area for myself.

Just to be sure to be sure I actually desoldered one of the pots and ran the meter over it. I had also read that somewhere about being purpose made....
They are though as stated 5K0 (give or take) linear pots, I would suspect that "purpose" made ones would have som sort of code on them to identify them as such because they would be made by the million.... My calculations are also quite close to the actual measurements. The good thing with this Hobby King stuff is it is as cheap as chips and seems to do the job. Guys flying very expensive aircraft report nil problems and really like the fact that the 6Ch TX can be programmed using a laptop in the field. If I stuff up the Tx its only $29 for a new one and the existing Rx's can be bound to it....
I'll replace the removed pot with my "solution" on one 1 channel and report back in due course though I don't foresee any problems apart from the actual soldering of the antenna coax. There are going to also be a few "logistical problems" associated with extending the wiring on some switches and the "bind" button, but any spmc button will do. I did suggest this to Hobby King and their response was that the market would be too limited so that left me feeling guilt free doing the mods to their stuff...

 

[Tony Walsham]

trev.
Just be careful selecting the radios.
There are two versions of the their low cost 6 Ch system.
They cannot work together.

 

[tramcar trev]

trev.
Just be careful selecting the radios.
There are two versions of the their low cost 6 Ch system.
They cannot work together.

Yes, I bought the Version 2 which will work with version 2 Rx. V1 stock is now redundant and not available through HK. Their stuff is standard though with industry, Tx battery is 12V Rx is 6V if you use alkalines or will accept Ni-Mh and runs ok at the lower voltage these provide. V3 is apparently coming out soon and when it does I'll scramble for redundant V2 Rx's
I can "bind" 99 Rx to the one Tx though I will probably lash out and get another Tx when the fleet grows and then I would share the roster between 2 Tx's as it's going to be easier to run with 2 motormen/women controlling things....

 

[tramcar trev]

I'm doing four pots in a handheld plus a button working the 5th channel.

Mock up pic.

Missing ON - OFF button and Ch # 5/binding button.
Working prototype this week.

Sorry Kev, this uses Deltang DSM2 stuff and I am not at liberty to divulge pot or resistor values.
"Edit, added the following":
Feel free to poke around the Deltang website for circuit diagrams, but, be warned the resistor values used may not be compatible as the system is based on 3.1 volts. I am not sure what voltages the system uses in a stick radio. Some Hobby King TX's use 9.6 volts for the TX module.

That looks very neat Tony. One minor criticism if I may; Its good to have it all in a compact size box but if you are going to use the box to control 4 channels plus 1 Aux and this suggests you could have speed only control over 4 locos + turn smoke etc on/off with ch5 then it would be better if you had the option of a bigger box with more space around each knob making it easier for those with big fingers to grasp the situation.
But for what we want knobs are far superior to joysticks, I have taken the springs out of mine otherwise everything is at half speed... R/C is also a lot less expensive (and less complex) than DCC.

 

[Tony Walsham]

That TX-5s is a 5 x Channel TX for Live Steam locos that require more than two servo channels. It is not meant for multiple loco operation, Just one loco at a time.
I showed it as an example of what is possible. It could be used for centre off battery R/C of one loco.

There are two other models each with specific operational capabilities.

There is no way I would ever make a bigger one as these TX's are intended for one handed operation of one loco, or group of locos.
I understand what you are trying to achieve. It is just not what I believe is physically possible without crashing something. However I wish you good luck trying.

 

[gregh]

Please Trev, can we have lots of pics as you pull the Hobbyking Tx apart and then rebuid it in your new 'box'. I've never had much luck 'reconfiguring' anything involving RF. Maybe 2.4GHz will be easier.
I'm not game to try anything like that yet, but if I can see how you do it, I might give it a go.

 

[tramcar trev]

Please Trev, can we have lots of pics as you pull the Hobbyking Tx apart and then rebuid it in your new 'box'. I've never had much luck 'reconfiguring' anything involving RF. Maybe 2.4GHz will be easier.
I'm not game to try anything like that yet, but if I can see how you do it, I might give it a go.

Ok... the RF bit is a separate little board connected to the antenna by thin coax and to the main board by 4 coloured wires.... The pots are held in place by wire clips and are the only bit I intend to change apart from putting the other boards in a new enclosure. I did a similar thing in the 70's with an old 2 channel 27mHz RC transmitter that I wanted for a model boat but I just relocated the pots then, not change them but It was in a very nautical looking brass bound dovetailed box and I used to get awards for the R/C and not my model ships....
If it works ( changing the pots that is) I see no real problems apart from resoldering the antenna coax. I will have to look at that more closely I may be able to surgically excise it from the HK case and put it in the new box on the joint line which would save me having to do the tricky bit of soldering....
But if pretty pictures is what you desire you shall have them.....

 

[tramcar trev]

Progress on the radio control is going along in top notch – now….
I wanted to “repackage” the radio control into a box with knobs (to be changed to miniature tram controller handles in due course). So as I have discussed with some of your earlier I took the transmitter case apart and was trying to work out how to make the 80 degrees movement of the joystick into 300 degrees rotation battling all the while trying to maintain the electronic “integrity” of the whole thing. So I looked at the bits and there are marked B5K which is a linear 5000 Ohm variable resistor so (and my reasoning was flawless) thus:

Problem; the potentiometers are 5K0 ohm linear ( that's what it says on the pots B5K0) but only the centre 60 degrees of the 300 degrees of "turn" are used and I want to replace the pots and be able to use the full sweep of 300 degrees.

Solution; as the pots are 5K over 300 degrees rotation then divide the 5000 by 300 = 16.6 Ohms/degree of rotation. Ok so then as I have the centre 60 degrees actually used there are 996 ohms in the swept area using the existing joystick. So if I use a 1K0 pot with a 2k0 fixed resistor on each "end" I end up close enough to 5K0 overall and the pot can be used for its full travel.

So just to be sure I measured one of the pots with a meter and the results were close enough to my theoretical ponderances…

Not sure when Murphy arrived on the scene but so just to be sure that this was going to work I soldered up the 2 fixed resistors and connected it all together only on 1 channel and gave it a try….. Nothing but a flicker of movement. For some reason I checked the pot again, the one I had removed and noticed in letters fully 10 microns high “80o”. Ahhh; then it all fell into place (Murphy had struck) these potentiometers used are specifically made for this purpose (as I had read on the net and pointed out by Mr Dim) so it was a simple matter to delete all reference to my calculations and simply replace the pots with 5K 300o ones – AND IT WORKED!!!! There is enough lead length so that I don't have to extend any of the wiring. I will need to extend the wiring for the on/off switch, the Bind button the battery level indicator and the charger input as these are mounted on the main PCB. My desoldering tool is going to get a work out.

Now it’s a simple job to mark out the new box, install the switches, buttons and battery charger socket. Then the battery holder and main PCB can be installed. I can see no reason why this won’t work unless Murphy strikes again…..
See I said it was going to be easy....

All the components incl bind button and redundant Pots.. Note the 12V battery holder and 12V on the circuit board.​

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[dunnyrail]

Trev
Great project, I can see this working to get rid of those horrible RC units for Live Steam too. Fingers crossed for total success.
JonD

 

[nicebutdim]

That's quite interesting. I was a little doubtful that they would use dedicated pots so before ripping mine apart I thought I'd wait until your results were published. Off to Maplins today then
Thanks Trev, your research has certainly helped me.

 

[tramcar trev]

Yes, there are numerous options. If you wanted to you could use slide potentiometers or even multi turn ones though they are a bit more expensive.

 

[gregh]

Thanks for the pics Trev.
I didn't realise how large the new 'box' is going to be - obvious when I think about it, if you need to fit 5 pots and the 8 batteries.
Anyhow, to be a smart alec, whydontcha just make a new front plate for the Hobbyking Tx with the 5 pots on it, to go over the existing 'sticks' ?
Then you don't have to do any desoldering for the charger, antenna, LV led etc.

 

[tramcar trev]

Size of the box was determined by the one I had. I'm not clever enough to make a new front for the hk box and I wanted mine to look home built as some will think I Made the lot. The ones I market in competition to the current Tchaikovsky stuff on sale will be of course far more professionally designed and ergonomically laid out.

 

[tramcar trev]

A few pics of the guts out of the box and the rewiring which was not extensive, the only bits extended were the charge socket, the bind plug (blue wires) and the power level and power switch... I also unsoldered the coax from the antenna so I can poke it through a new hole in the new box.
If it works I`ll put it in a smaller box maybe but I have big fingers and I like a bit of space around my knobs.....

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[tramcar trev]

Just one warning, this PCB is phenolic and therefore you need to use a bit more care with the desoldering and resoldering. Don't play around too much with this stuff as the pads can easily be lifted from the boards, I speak from practical experience...... No wonder they are cheap to buy I guess, the FR4 fibreglass boards are so superior to this stuff....

 

[tramcar trev]

OK all is looking pretty good, everything works - now.
My problem is that I don't fly model aircraft. The nomenclature for the set up of the HK 6Ch V2 Radio required some learning, I assumed that I could put "gear up" on Ch 6 and transmogrify that to simply turn on/off smoke on the steam tram HOWEVER model aircraftsmen are pedantic liitle types and "Gear Up" can't be used on CH6, aparently the gear has to go up smoothly not just with a clunk. The programme to programme the HK stuff is woeful, full of errors and graphic glitches. I did a search and found this program which is far superior, even I worked it out eventually....
http://www.sgr.info/usbradio/download.htm
Why did I have to programme anything at all I hear you all ask? Well because ch's 1 - 4 are assumed for aircraft use and the centre position is normal or "Off" and the ESC's I use (supplied by HK) thought centre was off except Ch 5 which has the reversing esc for the steam tram on it. I'm not explaining this very well.... So I reprogrammed the radio so that when my knobs are as far as they can go anti clockwise they are off, turning them clockwise increases speed except Ch5. I have one spare switch ( labled "Aux") which is there to maintain symmetry as yet I have no use for it but it could be used to turn the Tramway lights on/off or any such thing. I'll post some pics later....

 

[tramcar trev]

I now have my camera working again, it needed to be dropped on the floor to fix it and so here are the pics of the completed project.

The charge and programming sockets are on the left hand end and the bind button is on the right. I especially chose the bind button because it is IP67 rated and has a lovely tactile sensation when pressed. If you believe that then you`d believe anything, all the switches etc are from stuff I had at hand. I wanted to prove that this is possible and practical to do and it is. In due course this will be placed in a hand made wooden box with miniature brass tram controller handles as knobs and look like something from the V&A museum.....

The family Xmas is at my house this year and they all want to have a go at driving a tram.......