Variophon conversion

[Pchristy]

Work is now well under way on "giga-ising" the Variophon 10-channel transmitter kindly donated to me by Mike_K.

Here's the innards, with all the original Grundig electronics removed (and stored safely as spare for mine! )



The paxolin plate that secured the original aerial mount has been replaced by an aluminium one, to provide a proper ground for the 2.4 GHz aerial. The stick on the right has been removed, re-wired to suit the "Reeduino" encoder and replaced. Next up is the other stick unit.

The two buttons on the right of the image - originally for elevator trim - will be re-purposed. One will become the "trim" button, and the other the single-channel emulation button.

The empty spaces down each side of the chassis will have paxolin plates screwed to them (very retro!) to provide the mounts for the FrSKy "hack" module and "Reeduino" board.

Won't get much done over the week-end due to other commitments, but should forge ahead next week.

Watch this space!

--
Pete

[Mike_K]

Hi Pete

It looks like your conversion is coming along well.

One thing you mentioned though got me thinking. Do you need to mount the 2.4GHz antenna on a metal mount? Being blissfully unaware of this, on my Variophon conversion I have just mounted the antenna on a piece of fibreglass board where the paxolin aerial mount was (I've kept everything in case I should ever want to return it to original). It range checks OK, no different to any of my other 2.4GHz sets.

And in the past I've converted plastic cased transmitters to 2.4GHz without apparent problem. In fact I'm just finishing a 3D printed OS Pixie that is all plastic with no metal in sight.

Cheers

Mike

[Pchristy]

Mike,

Its probably not as important on 2.4GHz as on 27/35 MHz, but I do like to ensure that there is a good "ground" connection to the RF board somewhere.

When plastic transmitters started to appear on 35 MHz, they usually coated the inside of the plastic with some kind of conductive paint, or used a good area of metal inside to provide capacitive coupling to the pilot. In theory, any transmitter aerial other than a dipole needs a ground-plane reflector under it for best operation.

I think the aerials used in the 2.4 GHz transmitters are end-fed dipoles of some kind (I've never really looked into it!), so you are probably OK without the ground connection, but old habits die hard, and personally, I like to see one!

My advice would be that if its working OK, carry on as you are and don't worry about it!

--
Pete

[Pchristy]

Work continues, though at a slower pace than anticipated! A plumbing "malfunction" in the kitchen over the week-end and the consequential dealing with the insurance company has slowed things down a bit! And modifying the chassis to take the RF board has taken more time than expected. The chassis is made from steel rather than aluminium, which has made creating the extra holes required slightly heavy going!

Here's the chassis with the paxolin mounting plates in place:



Both stick units are now wired up. I've retained the cruciform limiters that prevent diagonal movement for the time being. This is how I used to fly one "back in the day", in "mode 1" (elevator on the left), and as I fly propo "mode 2", this might make it easier to remember what I'm doing! We'll see!

I had to cut extra holes in the steel top-plate to accommodate the bind board - quite a job - but its all done, and the bind board will mirror the original trim buttons:





The RF board is now fitted, and the wiring partially tidied:



Next job is to build, program and fit the "Reeduino" board. Hopefully all the donkey work is now done. I do need to find a suitable pot and mounting place for the "speed" pot, but have an idea for that. Hopefully it should be finished next week sometime.....

--
Pete

[tiptipflyer]

Hi Pete,
this will be a wonderfull reeds transmitter when finished. You will love it as much as I like mine.
I am using my converted Variophon for more than three years now flying everything from a Topsy, Taxi, Consul, Floride up to a Taurus. Never had a problem. I am using Phils old 10channel reeds encoder and a Futaba 35MHz module on the original antenna. The servo-speed pot is hidden in the battery compartment.
Most people know, that the enclosure of the Variophon used to be a AM/FM radio called "Grundig Moto Boy", here is a picture of it.

Frank

[Pchristy]

Hi Frank! Thanks for the kind words! Yes, you can see where the speaker was meant to fit in the plastic casings on the Variophon, but that is the first time I've seen a picture of the original radio!

My first multi-channel radio was a Variophon, back in 1965! Initially it was just 4-channels and super-regen. I had it in a Graupner Consul, powered my a Cox Medallion .09 and fitted the optional elevators. It was a superb model, and I flew it for years.

Sometime later, I was "gifted" a Super 60, which had previously been flown with an escapement and an ED Racer for power. I fitted a Merco 35, and bought the upgrade module for the Tx, a superhet receiver and the extra filter module for channels 7-8. I now had to get used to flying with the elevator on the left, but I never had a problem with it. After the Super 60 met its end (in an argument with a barbed wire fence!), I replaced it with a Graupner Taxi, powered by a Veco 19.

Eventually the Veco was taken to power my MicroMold Lark helicopter, the Taxi was sold, and the Variophon retired. I still have it, and it all still works!

The Variophon being converted is a 10-channel one that was very dead when I got it. I could probably have fixed it, but it seemed more sensible to convert it and use the parts as spares for my original one, should they ever be needed.

Those Grundig radios were stunningly reliable. Nearly everyone in our club had one - nothing else got a look-in! I always fancied one of their proportional sets, but they were very expensive when new, and never really caught on here in the UK. Maybe one day I'll find a nice second-hand one.....

Cheers,

--
Pete

[tiptipflyer]

Pete, if you really want a Grundig proportional set like the Varioprop 6 or 12 try ebay.de in Germany. Sometimes they sell for silly money, but sometimes you can get them really cheap. Last week I got a black varioprop 12 declared as unservicable for less than €10. The only thing broken was the coil of the the battery meter, the rest is working great.
The yellow varioprop 6, 8 or 12 sell a bit higher than the black ones, although the black ones are the better radios. The gimbals are much better, all metal instead of cheap plastic like in the yellow ones.
The Grundig TX14 is very hard to get, they sell for incredible money.
All the best
Frank

[Pchristy]

Frank, one question: When you modified your Variophon, did you keep the switches as standard, or did you modify them to allow diagonal movement? And what was the reason for your decision?

I'm just curious as I'm in two minds about this. Modifying the sticks allows more flexibility in control, but keeping them standard is more original. And in my case, may help with mode 2 vs mode 1 switching problems (I'm used to the Variophon having elevator on the left - or at least, I was!

--
Pete

[tiptipflyer]

I kept the Variophon as it was. I am flying mode 1 on all radios, primary stearing on the right, elevator on the left stick. As Phil mentioned, it´s a bang-bang (tiptip) radio, so it will be hard to give short pulses on two channels with one stick simultaniously.
We do not fly precision aerobatics on reeds, just leisurely flying around with a loop or a roll or two, or any combination of both. And of course a smooth landing on the runway! Or even better some touch + go´s.

Frank

[Pchristy]

Phil and Frank,

Yes, those were my thoughts as well. My original Variophon was only 6-channel (Rudder, Elevator and Throttle), which I flew with elevator on the left. I never had a problem when I got my first proportional and put elevator back on the right again, mainly because the two modes of flying were so different.

I asked because I think Mike_K filed out the gates on his transmitter to allow diagonal movement. I don't know how he's got on with that, but I can see both pros and cons. The biggest con being inadvertent application of a prime aerodynamic control!

On the other hand, retaining the gates makes control of take-off with a tail-dragger trickier as you can't apply elevator and rudder together (assuming ailerons on the right).

I'm going to leave it as is for the moment. If I do decide to remove the gate in the future, it will be on the left stick only!

As an aside, the Metz "reed" system (very similar to the Grundig) was a triple simultaneous system, and the gates on the RH stick were removable as standard.....

--
Pete