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

[leccyflyer]

Successful maiden flights for both the Digimac III and the Super 30 this morning and all went well. Having successfully range checked and failsafe checked the set up, we encountered a small problem with the motor cutting out when throttled up, which was cured by swapping out the motor for an identical unit from one of my SEMFF fighters ready for the maiden flight. That went without a hitch, even though I'd inadvertently left the 7x6" prop on, rather than reverting to the intended 8x6" prop. The Super 30 went away beautifully from a hand launch, though with a tendency to veer right a little - too much right thrust on my part, which I'll address with a couple of washers later. Once trimmed out the model behaved completely predicatably and encourage me to have a go flying On The Button, which was great fun. I did have to rescue a couple of over controlled uncomfortable position reverting to the sticks and after pootling around circuiting to left and right on the button, elected to land at the end of the flight using the sticks.

 

The mist turned to mizzle and stopped any further flights, but I'm pretty pleased with how the project has worked out and, after a few more test flights I'm sure I'll be able to try the Digimac III with my Outlaw before getting away from the safety net of those proportional controls and going full on single channel with the Gem 1+1 set. That's the plan to fulfill the aims of this excercise by the end of this flying season, fifty years on.

Edited September 17, 2023 by leccyflyer
typo

[leccyflyer]

Got two more of my wee MacGregor transmitters converted this week. It's quite addictive playing with old radios and Phil G's single channel and 1+1 encoders, plus the Lemon 2.4ghz modules make it a very straightforward job. I've been gradually getting into the swing of flying on the button with the Digimac III and find that I'm really enjoying the different mode of flying. 

 

Both are powered by a 2s1p 450mah lipo and the only changes to the case are a couple of wee peepholes to be able to view the status LEDs for configuration and showing the throttle status. The 1+1 has proportional rudder and sequential throttle -low-mid-high, which cycles through with each button press.

[yakacm]

On 07/09/2023 at 20:16, leccyflyer said:

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.

Wow, that's so nice soldering and wiring. I have an interest in old guitar amps, like as in valve amps, so I always appreciate some nice neat wiring, as well laid out wiring is something old amp nuts look for.

[Robert Thompson 10]

Help required. I’ve had a look to see where I can source a Tx hack module and associated receiver for a single channel project and also for a six channel project.

Everywhere I look, indicates as not available. Can anyone suggest a source with current availability please.

[Phil Green]

Do you have a favourite make/protocol in mind Robert?

Lemons are currently very popular. Try Stu Mackay, he's the EU importer direct from Frederick at Lemon:  https://www.ebay.co.uk/itm/133704108565

 

T9 Hobbysport may have Frsky modules in stock.

 

Hobbyking have the Orange module:

https://hobbyking.com/en_us/orangerx-dsmx-dsm2-compatible-2-4ghz-diy-transmitter-module.html  and also a Frsky JR-style module & rx combo

https://hobbyking.com/en_us/frsky-djt-2-4ghz-combo-pack-for-jr-w-telemetry-module-v8fr-ii-rx.html

 

I'm a bit out of touch with prices as I dont use commercial modules any more 😉

Cheers

Phil

Edited May 31 by Phil Green

[Robert Thompson 10]

Hi Phil, thank you for the info. I’m looking at converting some Futaba gear that I have. My first radio (S/C) and a Futaba M6 possibly.

I shall do a bit of further research before carrying out the work to make sure I understand what’s involved.

Many thanks for your guidance and where to source the items needed.