Wee MacGregor's In Control - bringing a 1970's 27mhz radio bang up to date

[leccyflyer]

Over the past few weeks I've been gently modifying a vintage MacGregor Digimac III 27mhz transmitter to 2.4ghz, using one of Phil Green's excellent encoders and a Lemon 2.4ghz module. It's all part of my recent vintage nostalgia kick, aimed at successfully flying a KK Outlaw with the 1+1 single channel set up, which I failed to complete a flight with in the 70's. At the time I'd scraped together my pennies from my various part-time jobs as a teenager, to get a Gem 1+1 set from Roland Scott's, a KK Outlaw from the Manchester Model Shop in Deansgate and a PAW 2.49RC from Forshaws in Wigan. What I'd always wanted though was the blue-anodised class of a Digimac Proportional set, but my funds wouldn't stretch to that.

 

Just this summer though, work on the Outlaw and a couple of punts on eBay saw me finally get hold of a couple of Digimac transmitters. In all a complete Digimac II set-up and Digimac III and IV transmitters only. I thought I'd start with the three channel set and thos was a nice clean example.

 

 

 

 

First step was to remove all the 27mhz innards, but to retain the On-Off Switch and with the intention to use Phil's encoder, plus a Lemon 2.4Ghz RF module from Stuart Mackay. I don't have any sophisticated test equipment, so it will be a simple function test and range check to ensure all is well. I've also got a plan for a wee depron Super Sixty -more like a Super 30 - to use as a test bed.

I followed the excellent document on the Mode Zero forum regarding set up of the encoder, with the assignment of the different channels, paralleling up the unused channels and getting the three main function connected to the existing pots. I wanted to maintain the look of the transmitter externally, with the only addition so far being a S/C button on the front fascia, beneath the main flight control stick in Mode Two configuration. Having read on Mode Zero of the benefits of flying On The Button, but with a safety net of the rudder-elevator propo stick to hand. I wasn't sure of the preferred position for the S/C button, so intended fitting another, on the top right of the case and having one sequential and the other compound.

The other thing I considered vital was a throttle cut switch, as on my existing modern transmitters for electric flight - a long throw 2 position switch on the top right of the transmitter. Unfortunately the supplier sent two short throw, 3 position switches by mistake, so that remains to be fitted. Once that is in place I'll be able to fit the second S/C button. I've made provision for rates and expo internally, using the pots recommended in response to my question on Mode Zero. I 3D printed mounts for the encoder, RF module and the rate and expo pots, plus knobs for those pots. I decided against having the rates on a switch, but that might conceivably change.

Power is provided by a 2 cell 2800mahl Li-Ion pack, which fits nicely in the space beneath the rates and expo pots mount. The 3D printed mount for the RF module resembles an oil production platform, supported on four nylon bolts which engage with captive nuts affixed to the case with double sided tape. That positions the aerial connection in the ideal location to accept the short antenna as it emerges from the 2,4ghz aerial housing.

 

 

 

 

Phil Green was a great help again in providing some Zener diodes and resistors to make the meter function as an extended range meter, compatible with the 7.2v Li=Ion pack. I'm just waiting to fit those last two switches before the grand switch on and keeping my fingers crossed that the magic smoke signals don't spoil the show. Ultimately I want to dedicate this set to operating my Outlaw and, assuming that's successful, will make the same conversion on my Digimac IV, probably to drive my forthcoming Mini Super.

 

The Pontefract retro fly-in back in July was a great catalyst to encourage me in this project. The single channel and vintage enthusiasts over on the Mode Zero forum have been marvellous, as their collective knowledge and encouragement has made this first attempt at a conversion so enjoyable, but especial thanks to Phil for answering the daft questions of a complete electronics neophyte and providing such super support throughout.

Edited September 7, 2023 by leccyflyer
Added picture

[Graham Bowers]

Had the same set back in the day.

 

Great project and I sometimes regret skipping mine - then I remember the reality.............

 

Wee MacGregor sometimes had control, in my book, often in a spiral dive 😉

[Roy Thompson]

The Digimac III was my first radio, my big brother brought it for me. That poor radio took a lot of abuse over the years, good job we lived near their factory. I made regular visits there for repairs and to have it upgraded to four channels. 

 

Looks like a fun little project.

[Masher]

Hi Leccy. Nice story and description, well done for pushing your boundries.

Please make sure Phil has a good look at your pictures before you switch on though because it very much looks like you may have short circuit around the orange cable area at the module. 

Hope all goes well

Martin

[Paul De Tourtoulon]

I had the Digimac 4, the worse thing that I ever bought !, looking back maybe it wasn't thier radio but the servos that they made, but it did crash 90% of my planes.

 

Nice job that you are doing.

[leccyflyer]

Thanks Martin - good catch, you're quite right, the signal wire was just touching the telemetry contact on the module. 😮

 

I've redone that solder joint. I

 

 

 

'm sure it's not a candidate for a Queen's Award to Industry but it's definitely not touching now. Thanks again for that great catch Sir 😎

[Masher]

Well done, much neater 

 

 

[leccyflyer]

57 minutes ago, Paul De Tourtoulon said:

I had the Digimac 4, the worse thing that I ever bought !, looking back maybe it wasn't thier radio but the servos that they made, but it did crash 90% of my planes.

 

Nice job that you are doing.

I'm using modern servos and receivers for these projects, so there's little remaining of the original MacGregor sets, other than the stick units and that gorgeous blue anodised brushed aluminium case. I have a box with several Elmic escapements and a few 27mhz receivers with the big bulky MacGregor servos, but those won't be going in a model.  It's pure nostalgia and has opened up a whole new part of the hobby for me this summer. 🙂

[Wookman]

Nice work Leccy.

[Outrunner]

Very nice Leccy, I hope you enjoy flying with them.

I've converted three MacGregor sets now. 2,3 and four channel, I've given the 4c set to my I son I use the 2c in my Tomboy and the 3c in my Junior 60. I used Lemon modules and Phil Greens decoders and they all work a treat. The Macgregor stick units are  not exactly cutting edge but they work. The right stick on my 3c set creaks and makes fellow flyers grin, but they work 

I also fly my J60 on the SC button, great fun and when I get into a pickle trying to remember two pushes for right etc I just get back onto the stick to recover.

Enjoy 

 

 

[leccyflyer]

That great to hear and sounds like exactly what I'm after Outrunner, 😎 it'll fulfil an ambition when it finally happens - the weather at the moment is perfect, have just had a few hours of blissful flying in zero wind, hot and sunny weather after the early mist burned off. I'd hoped for a bit of an Indian Summer and I think that's where we are at for now. The postie has just delivered the replacement switches, so I can make those final connections now and get the set range checked.

[leccyflyer]

Had a Road To Domestos moment yesterday morning, but thanks to Phil, who advised again on one of my misgivings the set was saved from going down the pan. I'd just copied Wee MacGregors wiring on the stick pots like for like, but on reading again, for the hundreth time, the document which accompanies Phil's encoder suddely realised that the central tab on the pots was for the signal, not the positive. Phil confirmed that was the case and a few minutes with the soldering iron rectified the problem. I've included a replacement pcture of the amended connections to those pots, just in case anyone uses this thread as a reference.

 

 

There was no putting it off any longer I finally had to switch on and everything worked, eventually. I justtested the set with a loose spare receiver at first to check all was working before committing to a test with a model. After the stick calibration and some adjustment for reversing the controls everything checks out fine. The throttle lock works, the failsafe works, rates and expo work, the two single channel buttons work giving sequential and compound emulations. Here's how the finished set looks. GThrottle cut switch top right, compound s/c button in front of that and sequential s/c button on front right below the elevator/aileron stick.

 

 

Next step is a range check and flight testing. I don't really want to risk the Outlaw for the first go and, since my pal Bob has such great fun with a half sized profile depron Super 60, i thought I'd knock one up as a test bed. Fuselage halves are just curing as I write, wing is all ready to be joined later and the bare model should be done and kitted out shortly.

[Phil Green]

Excellent, well done Leccy, a 'period appropriate' transmitter adds so much to the fun flying retro models, but beware the process is addictive, its quite impossible to do just one conversion - this will be the first of many!  😀

Yesterday I was at Ivinghoe Beacon in a lovely 15mph westerly, had four long flights with the Jack Kay "Moonbeam 2" which is rudder-only single-channel on the  OS Pixie, and several more with the Veron Impala which is on rudder-elevator Reeds.  The disbelief of local flyers is a joy to see, one local had a go at Reeds for the first time in 50 years and couldnt stop giggling 😀  None of the dozen present had ever seen S/C slope soaring before and so there was as much reminiscence banter as there was flying!

All great fun and very relaxing, its nice to get away for a few days and fly somewhere different 😉

Cheers

Phil

 

 

 

 

[leccyflyer]

Well Phil - you are totally instrumental in making this project work - I don;t know where I'd have been without your support and answering my daft noob questions, as someone who has no experience of electronics beyond the usual electric flight bits and pieces. It was a marvellous learning experience. Thank you so much.😎

 

I'm sure that there will be follow up conversions, I have three other vintage sets to convert that are sitting there in the pipeline. I foresee an Impala and hopefully a KK Chief in my future, as the latter was one of my more successful models flown free flight from a towline and the former is what I imagined slope soaring was all about, decades before I ever saw one for real.

[John Wagg]

Nice work Leccyflyer.

I converted my Futaba Challenger to 2.4 a couple or so years back. Just as a project and for fun.

What I do wonder is it legal to use as it is not EU/LBT protocol (D8) ?

The Challenger, same as the MacGregor, is obviously pre-2015 which I understand is when LBT was introduced. 

 

 

Edited September 12, 2023 by John Wagg

[leccyflyer]

Thanks John - the best information I have is that it is perfectly legal to use, as the important bit, namely the  RF module, complies with the appropriate regulations. So it's every bit as legal as any legacy set with an aftermarket module, just like the FRSKY module that I've been using for the past ten years or more in my Futaba FF9.

 

I had a pair of Challengers as my first 35mhz sets and donated them for club buddy box use when I upgraded to FF8. For a time they became quite sought after as they had a significantly more powerful RF stage than other transmitters. They were very nice, quality sets to use and well worth converting and preserving.

[John Wagg]

Thank you. That's good to know.

I also still have an FF7 on the shelf but much preferred the Challenger to use.

Cheers.

 

[Paul De Tourtoulon]

Can't you use the old McGregor ariel and hide the 2.4 one somewhere ?.

[leccyflyer]

I'd rather replace the old aerial with the new one, much neater.

[Outrunner]

2 hours ago, Paul De Tourtoulon said:

Can't you use the old McGregor ariel and hide the 2.4 one somewhere ?.

What are you suggesting, hide it inside the metal case?

[Phil Green]

Repost: Hidden 2.4ghz transmitter aerials

 

Edit:

er... hang on, sorry, that's not the thread I had in mind...

 

this one (& others similar)

https://mode-zero.uk/viewtopic.php?p=712#p712

and

https://mode-zero.uk/viewtopic.php?f=52&t=245&p=977

Edited September 12, 2023 by Phil Green

[leccyflyer]

Thanks Phil.

 

I thought for the 27mhz RCS single channel set that putting the 2,4ghz aerial inside the frequency pennant like Paul has done might be an option. TBH you could fit an old set of TV rabbit's ears inside the case, together with a lucky rabbit's foot and still have room for a module. For what is in there it's a massive case and I'd forgotten how long those 27mhz aerial are - like a fishing rod.

[Phil Green]

Each to his own, Paul likes the fishing rods, I prefer the standard 2.4 aerials, so mine are all like your Digimac 😉 

I often find the aerial mount is the hardest part of a conversion, much easier if you have a 3D printer (I dont!)  😁

 

Edited September 12, 2023 by Phil Green

[leccyflyer]

Well if you ever need anything 3D printing, I have and I'd be delighted to provide you with 3D prints.

[leccyflyer]

Quick test bed aeroplane for flight testing the Digimac III all ready to go - hopefully tomorrow if the weather co=operates. Thankfully all the controls worked in the same direction as on the Outlaw.

Not very traditional, but a proven design and only a few hours work, a half size 32" span profile Super 60 in laminated 6mm depron, with 20g pole and stator outrunner, 10amp esc, 2s1p 800mah pack and 8x6" prop. That set up works well with my <250g SEMFF funfighters and also with my pal Bob's identical model. AUW is 260g - I could have got it withing the 250g limit with a lighter undercarriage, or by not having a dihedral brace, but I don't mind the extra 10g too much.