New Digimac 1+1 revision 3, a few more bells & whistles

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Phil_G
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New Digimac 1+1 revision 3, a few more bells & whistles

Post by Phil_G »

The original Digimac-1 by Macgregor had just a proportional rudder servo and nothing else, no throttle and no rudder trim. Macgregors 1+1 update gave the set a sequenced throttle servo - low, mid, high, mid... repeatedly, changing once per push of the throttle button. Years ago I did a PIC encoder which exactly emulated the Macgregor 1+1 in every way, no extras or refinements - just an accurate emulation.
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The Macgregor Digimac 1+1
The Macgregor Digimac 1+1
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Here is an improved version of the "Digimac 1+1" based on the cheap-as-chips Digispark ATtiny85 board. The Digispark is a tiny 3/4" square Arduino thats really convenient and dead easy to use as the headers have the normal 0.1" spacing. I always remove the redundant USB plug, and also the redundant SMT diodes D1 & D2 which can be removed with your thumbnail (as explained here).
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Digispark USB removed...
Digispark USB removed...
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This emulation adds a few facilities over Macgregors original, all of which are optional but I think should prove useful in practise. Its basically a stripped-down edit of the 7ch encoder, with Franks throttle idea and some "1+1 specific" bells & whistles added: Auto stick calibration, throttle position confirmed by an LED which is off for low, flashing fast for mid (where next speed is high), solid for high throttle, and flashing slow for mid (where next speed is low). There is also a buzzer which pips once for low, twice for mid and three times for high throttle. We have rudder subtrim, by holding the stick over in the required direction whilst dabbing the throttle button. Trim is saved to flash memory. It has a presettable mid-throttle position, so it no longer needs to be exactly 'half' - half throttle sometimes doesnt suit a model, it may be a bit too low or too high to maintain a steady cruising height. IC engines rarely have a linear throttle response, and the half setting might well give 80% power.

Stick calibration as always is by switching on with the button held in, & keeping it held in, waggle the stick (& trim if it has one) to its extremes. Then you allow the stick to centre, centre the trim (if there is one) let go of the button, and the set springs to life. This will calibrate the stick and will also set mid-throttle to half, exactly like the original where mid-throttle is always half. To set medium throttle somewhere other than half, at the end of the calibration process, instead of allowing the stick to centre, hold the stick slightly off neutral as you release the button. The amount of offset from neutral will be the new mid-throttle setting, and is saved to flash, so the setting remains in place until you deliberately change it.

It has the usual reversed rudder on channel 4, this saves changing the transmitter setup between models if the rudder happens to be opposite. If you do find some reason to reverse the rudder channel, simply power-on with the rudder stick held right over. The reverse setting is saved to flash.

Throttle: Exactly like the original 27Mhz 1+1 the throttle is sequential with low, mid, high and back to mid in a continuous cycle. Every brief dab of the button moves the throttle to the next setting. Selecting low sounds one pip. Mid sounds two pips. High sounds three. This lets you know where the throttle is set. The throttle can be instantly cut from any position by holding the button briefly rather than blipping it, this was Franks idea (thanks Frank!)
Like the S/C bang-bang encoder, the throttle LED is off for low, fast flashing on mid throttle, on for high, then slow flashing for mid throttle – the mid-setting flash rate indicates the next throttle position, so we now have audible and visible throttle indication. All this pipping and flashing is synchronous & doesnt affect the timing. For convenience, I used a 5v LED to avoid the resistor.

Rudder trim: Whilst the original Macgregor Digimac 1+1 had no rudder trim at all, this revision does. It gives you fifteen 'digital trim' steps of 10uS in either direction, by holding stick slightly towards the required direction & pressing the button – each trim step 'pips' as you would expect. 10uS is a typical 'trim pip' on most modern sets. Trim changes are saved to flash so they are retained ready for next time you switch on. It might be that 10uS is too small a change, maybe 20uS would be better, lets see how it goes.

So the throttle button now has two functions - when the stick is at or near neutral, it acts as the sequential throttle just like the 1+1 always did, with Franks immediate throttle cut by holding it down - ideal for an unplanned arrival, or if you forget whether your 'mid setting' was on the way up or down.

If the stick is thrown partly either way, then the throttle button becomes the 'trim' button. In practise its easy to flick the stick over & press in one quick movement, and if the trim is a long way out, you can rapidly press several times to get several steps of trim. Even so, I expect the trim facility will be used more on the ground for initial setting up than in the air. It has the usual inactivity timer which sounds if there's no stick movement for 10 minutes.

Programming the Digispark needs the home-made ICSP adapter, you cant use the USB bootloader as it has a 5 second startup delay (yes, five seconds!). This means that for 5 seconds, your set would be powered up but not sending any PPM to the module. Corona modules default to 500uS channels in the absence of PPM. 500uS is so far outside the usual 1000 to 2000uS range, that this can cause servos to jam against the end stop and even strip gears. In any case a 5-second power-up delay is not acceptable for a transmitter, so ditch the bootloader!

One thing I've noticed with one or two Digispark boards is that the clock frequency (nominally 16mhz) is stable but can be a little bit out. In the datasheet the manufacturer states that the clock is factory calibrated to within 10% but can be further calibrated by the end user to within 1% using an oscillator calibration register.
Out of dozens of Digisparks I've only found a couple that benefited from a 'tweak' of the timing. If yours is badly out, then in setup() I've included an optional OSCCAL setting where this can be compensated - though its a bit trial-&-error. To avoid recalibrating every time its easier to check the elevator channel and adjust OSCCAL in units of say 5, until the elevator is near enough 1500uS.

If you've not yet built a PPM tester then comment out the OSCCAL line, it won't be that far off without it, whereas a 'wrong' or guessed OSCCAL value could be way out. And once you've 'osccaled' a chip, the factory value is gone, overwritten - theres no 'restore factory defaults' :-)

So far I've been sending these encoders out pre-wired with flyleads and shrink-wrapped, but the files are items P20 and P21 on the Archive page of http://www.singlechannel.co.uk if anyone fancies a go. The biggest pain is connecting up a 6 negative wires into one, so it will solder into the solitary 0v hole. Thats stick neg, button neg, LED neg, buzzer neg, battery neg and RF module neg all commoned together into 1 wire, bit of a Medusa-thing going on there but thats the beauty of heatshrink - who would know? :lol: :lol: :lol:
Quite a few pre-wired Digispark encoders have gone out and feedback has been good. I'll do a demo video as soon as I get chance. Oh - one last thing - if you use a 'Frsky V8HT' or a Corona module dont forget the schottky diode in series with the PPM line, banded end to the encoder (BAT42 etc).
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The Digispark board, 3/4 of an inch square!
The Digispark board, 3/4 of an inch square!
digisparkboard.jpg (68.96 KiB) Viewed 18797 times
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Lots of negs into one hole!
Lots of negs into one hole!
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Prewired board as I've been sending out
Prewired board as I've been sending out
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Connections P0 to P4, P5 usnused
Connections P0 to P4, P5 usnused
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Cheers
Phil
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digimac1plus1_mk3.pdf
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Shaun
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by Shaun »

This is brilliant - I may just update my 1+1 even though the original still works perfectly.

Shaun
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tiptipflyer
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by tiptipflyer »

Here is on of my latest conversions, an ACE Pulse Commander. It uses Phil´s latest Digimac MK3 sketch without the trim function, which is not needed here. Flight test happened already flying a Sharkface with Tobe´s Adams clone. No problems, everything worked perfectly.
SAM_3100.JPG
SAM_3103.JPG
Sharky4.JPG
Cheers
Frank
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RON
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by RON »

That’s a very nice Transmitter Frank,

I wouldn’t mind a go at reproducing one of those, that red car leather stuff might work well on that.

Ron
G0MBV Class A Radio Amateur, North Yorkshire
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Wayne_H
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by Wayne_H »

I'm well on the way with my own version - all the bits are assembled & working perfectly on the bench.
need to shorten some of the wiring and then put it in the box
need to shorten some of the wiring and then put it in the box
Being 'frugal' (i.e. a tight ar :o) and having a few in my components box, I've decided to use a dual axis game console PS type stick assembly - since I only need a single axis, a slotted hole in the case will effectively 'remove' the 2nd axis function.
the original 'gamer' knob in the background, plastic shaft threaded 4mm for the "bling" stick extension. The stick shaft has a 1.5mm hole down its axis, which I deepened and glued a piece of wire into to make the whole assembly a bit stronger (I hope!?!).
the original 'gamer' knob in the background, plastic shaft threaded 4mm for the "bling" stick extension. The stick shaft has a 1.5mm hole down its axis, which I deepened and glued a piece of wire into to make the whole assembly a bit stronger (I hope!?!).
stick extension added. The nylon stand-offs enable the assembly to be mounted to the front of the case.
stick extension added. The nylon stand-offs enable the assembly to be mounted to the front of the case.
These units also feature a push-button function, which I shall try. It works perfectly on the bench, but if it doesn't feel right when flying, I'll simply use a separate button.
showing the push button which has a very positive action, press down on the stick to activate.
showing the push button which has a very positive action, press down on the stick to activate.

Now to attack the enclosure...........
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
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Wayne_H
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by Wayne_H »

OK, it all fits & it works too :D
Its only a cheap plastic case off Ebay, but it'll do! The slot for the stick had to be opened out at the ends to allow full stick throw due to the short length of the plastic shaft and the stick extension. Looks odd, but it works!
Its only a cheap plastic case off Ebay, but it'll do! The slot for the stick had to be opened out at the ends to allow full stick throw due to the short length of the plastic shaft and the stick extension. Looks odd, but it works!

If I were putting it into a metal case, I'd clad it with stick on vinyl to hide the screws. The plastic case has too many ridges & rounded corners for the vinyl to adhere to without peeling or lifting.
red button is in parallel with the button on the stick assembly
red button is in parallel with the button on the stick assembly

I found an issue with the push button integrated with the stick. It only works consistently when the stick is at or near neutral. Consequently, I added the separate button.
Had to have a label...............
Had to have a label...............
label_s.jpg (17.54 KiB) Viewed 18698 times

It all looked too plane & dark without something to contrast, hence the tongue-in-cheek label :lol:

Hopefully to be test flown on the weekend.
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
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_AL_
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by _AL_ »

Nice.
How do you find those little gimbals? Do they give you a smooth action or are they a bit on/ off?

Al
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Wayne_H
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by Wayne_H »

They feel surprisingly good Al, especially for the price. The resolution and linear servo response on the bench are great.

Of course, there is absolutely nothing "exotic" about them like adjustable stick tension, etc. I reason that they must be relatively robust given the gamer application - I've never seen a gentle-on-the-gear gamer when in the heat of battle :roll:

I'll update you after test flying ;)
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
FBMinis
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by FBMinis »

Making a 4mm thread was a great idea which actually helped me. However, I used a plastic screw anchor or appropriate size, as this way I can take advantage of the full deflection of the pots.

Thank you!
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Wayne_H
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Re: New Digimac 1+1 revision 3, a few more bells & whistles

Post by Wayne_H »

Glad I could help :D

That's a "space age" looking enclosure - make sure you set phasers to stun before you fly a model with it :P
Cheers,

Wayne
Once a Retrobate, always a Retrobate............ ;)
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