Krafts for the 21st Century

[stuart mackay]

One of Lemon's best customers has sent me some photos of his Kraft Mk III in twin and single stick format.
These have been cleverly converted utilising the original encoders feeding a pulse into a Lemon DIY module with some clever circuitry to adapt the short Kraft trigger pulse to suit the lemon 2.4 module. Anyone who knows these later style of plug-in RF module of Krafts, will know that the conversion to 2.4 GHz is not as straightforward as it seems. Together with his electronic expert friend, a new board to replace the existing Kraft RF module design some circuitry to enable the packaging of the Lemon module within the original Kraft plug in module case.

The major advantage of this is that the module is still able to plug in using the original socket and work both meters (Battery V & " RF") where applicable.

Similar Plug and Play conversions utilising the Kraft synthesised module are offered in the States, and these UK produced modules are the first to use the more compact modules more commonly found in later Kraft transmitters.

Here is a small batch of the Lemon 2.4 modules installed in the Kraft module case:

If anyone is interested in one of these, we have a small number of boards designed specifically to install a lemon DIY module and can offer a conversion service using your original Kraft module case and plug as donor parts. Please get in touch if interested?

Here is a before and after of a Series 75 using Mike's encoder and Lemon RF module:

[Pchristy]

Very neat work!

--
Pete

[stuart mackay]

And here is my Bi-centennial series converted using the new plug in module/lemon DIY combo.
Hope you can see both meters working too?

[Pchristy]

Excellent job! Muchos kudos!

--
Pete

[GardenGate]

Hi Stuart - I would love to get more info on the circuitry used to adapt the Kraft trigger pulse for the Lemon module (and I'm probably interested in getting at least one of the boards). I have a couple of Signature Series transmitters which I want to leave as original as possible, so fitting the Lemon module (plus whatever other circuitry is needed) into the original compact module would be ideal.

[stuart mackay]

Hi Stuart - I would love to get more info on the circuitry used to adapt the Kraft trigger pulse for the Lemon module (and I'm probably interested in getting at least one of the boards). I have a couple of Signature Series transmitters which I want to leave as original as possible, so fitting the Lemon module (plus whatever other circuitry is needed) into the original compact module would be ideal.

PM sent

[stuart mackay]

No Secret, Phil, just that it was designed by a friend and I respect his technical confidentiality and do not have his permission to share his design.

[Phil_G]

I dont follow Stu, from the service docs, though channel timing is slightly different the Kraft PPM frame seems totally conventional,
and their 8ms sync is plenty for the Lemon module I'm intrigued how you're extending the sync inside the Kraft module?
Kraft conversions are quite popular on RCG using only a level converter - was Andy's Kraft different in some way, maybe modified?
The only (occasional) problem was that the original encoder was prone to power supply noise generated by the 2.4 module, which
some cured with a separate battery and others with an emitter-follower impedance dropper (like in Terry Tippet's Micron rx)

[stuart mackay]

I dont follow Stu, from the service docs, though channel timing is slightly different the Kraft PPM frame seems totally conventional, and their 8ms sync is plenty for the Lemon module
Kraft conversions are quite popular on RCG using only a level converter - was Andy's Kraft different in some way, maybe modified?

Dont know Phil, but I ll find out and get back to you,

[Mike_K]

Dont know Phil, but I ll find out and get back to you,

Phil, the Kraft is near standard ppm timings in the range 0.9mS-1.4mS-1.9mS. But the circuit diagram I found for a 7C had an open collector pnp output which a LemonRx (or FrSky or OrangeRx) will not work with without a pull down resistor minimum. Most just buffer the signal with a transistor, then it will work with any Kraft module set.

Next the Kraft encoder can be sensitive to RF noise back into the encoder so many fit an inductor/capacitor filter to the LemonRx module power supply.

I think what Stuart's friend had done is fit all this into the plug-in RF module so it is plug-and-play, you take your 35MHz or 72MHz module out and plug in the 2.4MHz module (just like you'd do with a JR or Futaba). Not everybody is happy with a soldering iron, so this is a convenient and painless way of converting the classic Kraft set to 2.4GHz. And it keeps the set original, if in the future they want to revert back to 72MHz,, just swap modules over.

The Kraft module cases are like gold-dust there just are not many spare ones available. And the connector in the module is a custom Kraft moulding, when Kraft finished, Royal bought the tooling then it closed and the remaining stock has gone. This is where Stuart has been clever, he found some new-old-stock cases for the conversions.