Looking to convert a 1975 MRC Single Stick 4 channel to use the XHT module

[ej_flys]

Hi,

I have a real nice never use MRC F-724 single stick from the mid 1970s that I would like to use the existing hardware and just connect in the XHT module.

YouTube video showing the transmitter:

The transmitter works now fine on 72.

I just got a new 9.8 Eneloop battery and it works great but I don't want to use it on 72. It is not narrow banded so I am sure it is illegal to use.

I had one of these exact transmitters when I was a kid in the 70s that I flew with my father.

I have the XHT module and connected it up to the the PPM signal from the MRC but I don't think the PPM signal is right.

I connected the XHT module up to one of my JR Century 7 single sticks and it works fine and I was able to bind to the receiver and the servos worked fine.

I have a cheep scope and it shows a PPM signal showing 4 channels but not as close to the signal pattern from the JR.

Any ideas?

Thanks,

Evan

 

[Wayne]

If it is doing something odd for a PPM, more drastic measures may be needed. The XHT is pretty capable of working with many PPM issues, but if it is doing it's own take on PPM the XHT will not be able to decode it.

 

[ej_flys]

Wayne,

Success!!!

Thanks for the reply. I checked one pad over on the main board and found higher voltage that was driving the signal as well and it works!!!

Thanks,

Evan

 

[Wayne]

Great!! If the radio is still open, share a photo, never know, someone might come along looking for the pad locations in 5 years..

Thanks!

 

[ej_flys]

Hi,

Attached is the completed project showing where I soldered the wires to the main board.

The issue I was having is I first found the signal on the trace to the right of where I have the green wire currently soldered in the picture. I found the weak signal first and stopped checking but since it was not strong enough I started searching with my cheap scope and found a stronger signal to the left of the trace I was using. I then connected it and tested it and it worked perfectly.

I made this so I can easily reverse the changes if I wanted to put it back to the original configuration for whatever reason.

It is basically all stock except for wiring in the XHT board and replacing the 72 MHz antenna with the 2.4 GHz antenna.

I am using a blank circuit card to connect the XHT board to the main board and just velcro it to the bottom of the case. The pinout is the same as a JR style module.

I can easily disconnect it or swap it with another card if I want. I have a 4-in-1 card too that I may try at some point.

To disable the onboard 72 MHz card I just pulled the crystal ( it would have been where the metal holders are on the bottom right side of the green card, F820R, in the second photo attached).

The signal power meter, on the front of the case, does not work with the XHT card because it is connected to the F820R board and I did not want to mess with that now if I want to keep it original.

There are some hacks on the internet to convert the signal meter into a battery meter but I wanted to keep this transmitter as stock as possible for now. Maybe later....

Hope this will help if someone is trying to convert a similar transmitter like a KRAFT or other.

Thanks,

Evan

 

[Wayne]

That is great!! Thanks for sharing this.

 

[Konrad]

Love the detailed photos. Is this a dual band radio? I ask as I see that the green board is labled 72 mHz.

Wow, I had that Jr Century radio. I loved how it felt. The trim pots and throttle where much better than what I had on my MicroPro800 Single Stick. But the MicroPro was a computer radio and offered the mixing power that pots and Op amps just couldn't

Is this your hobby upgrading old radios to modern RF standards?

 

[iflylilplanes]

Nice build, I'm about to convert a 1970 Futaba 4ch to 2.4gig, have a try anyway.

Just wondering, is there a manufacturer making linear servos these days? had linear servos with my 1973 Futaba 5ch, rotary ever since.

Not looking for any, just wondering.

 

[ej_flys]

Love the detailed photos. Is this a dual band radio? I ask as I see that the green board is labled 72 mHz.

Wow, I had that Jr Century radio. I loved how it felt. The trim pots and throttle where much better than what I had on my MicroPro800 Single Stick. But the MicroPro was a computer radio and offered the mixing power that pots and Op amps just couldn't

Is this your hobby upgrading old radios to modern RF standards?

Thanks...

I ended up removing the 72mhz board since I removed the 72 mhz antemma. I did not want to cut holes in the case so came up with a 3d printed part to mount the antenna and XHT bind board.
I dabble with converting old transmitters into 2.4 and have an MS2k in the works plus a Open TX Arduino board too. To much other stuff at the moment to finish them but at least this one is done and was quite simple.

I love the old single sticks but do fly Spektrum and JR factory dual sticks as my main transmitters for now.

 

[ej_flys]

Nice build, I'm about to convert a 1970 Futaba 4ch to 2.4gig, have a try anyway.

Just wondering, is there a manufacturer making linear servos these days? had linear servos with my 1973 Futaba 5ch, rotary ever since.

Not looking for any, just wondering.

I have not looked for them but they do make more sense. I think I saw a kit to convert a servo into linear. May have seen it on one of those robot sites. Good luck.

 

[ted]

Hi,

I have a real nice never use MRC F-724 single stick from the mid 1970s that I would like to use the existing hardware and just connect in the XHT module.

YouTube video showing the transmitter:

The transmitter works now fine on 72.

I just got a new 9.8 Eneloop battery and it works great but I don't want to use it on 72. It is not narrow banded so I am sure it is illegal to use.

I had one of these exact transmitters when I was a kid in the 70s that I flew with my father.

I have the XHT module and connected it up to the the PPM signal from the MRC but I don't think the PPM signal is right.

I connected the XHT module up to one of my JR Century 7 single sticks and it works fine and I was able to bind to the receiver and the servos worked fine.

I have a cheep scope and it shows a PPM signal showing 4 channels but not as close to the signal pattern from the JR.

Any ideas?

Thanks,

Evan

I have a Kraft like this. On mine the tap on the battery is because the servos use plus and minus to go left and right , only 2.5 volts each way instead of a bridge circuit. Be careful that the servo cases aren't the type of plastic that falls apart.

 

[Txmustangflyer]

Nice build, I'm about to convert a 1970 Futaba 4ch to 2.4gig, have a try anyway.

Just wondering, is there a manufacturer making linear servos these days? had linear servos with my 1973 Futaba 5ch, rotary ever since.

Not looking for any, just wondering.

Yes, there are linear servos available.

Linear Servos for RC and Arduino | Actuonix Motion Devices

www.actuonix.com

I haven't done the gear door servo installs on the mustang yet as I'm considering using a set of those to run the gear doors instead of standard servos. Still mulling that one over.

Same company also makes linear actuators for rc as well. Main problem is trying to figure out what stroke length is needed.

Prices are pretty reasonable.

 

[Konrad]

Nice build, I'm about to convert a 1970 Futaba 4ch to 2.4gig, have a try anyway.

Just wondering, is there a manufacturer making linear servos these days? had linear servos with my 1973 Futaba 5ch, rotary ever since.

Not looking for any, just wondering.

I'm not aware of this old (modern 3 wire) configuration still being manufactured.

 

[Txmustangflyer]

No..not tjat particular one, but they do make something similar. Actuonix makes modern, 3 wire, linear servos.

The PQ12-R would be the closest to yours, pictured. Two, together back to back, wpuld give same function as above. Instead of linkages hooking on the top, they are on the end, allowing longer throws. Their stuff is programmable, but like most digital servos they are set at factory for full travel, meaning you don't have to.

Afaik, actuonix are the only source for linear servos nowadays. The question was if there were still linear servos available. The answer is, yes. Exactly as they used to be, no. They have advanced right along with standard servos in tech. They also make switxhed throw actuators, step motors, etc.

As thin as most of your wings are, Konrad, I'm actually surprised you had't foynd them already. Actuonix makes them specifically, for applications where space is at a premium. Seen the actuators used for sliding canopies. Their servos have been used dor rudders, and flaps, even ailerons on occasion. They are veey compact and due to being linear, seem to not suffer from the wear problems of a standard servo over time.

I, myself, have never used them, but, as I said, am considering a pair for the Mustang's inner dear doors. As those doors open and close on each gear cycle, up or down, reliability is a must, otherwise the gear would crush the doors. Reliability is the very reason I am considering them. Being digital, and programmable, would make setting up the movement of the doors much easier. Instead of having to continuously pop the linkage loose and spin the collets, simply adjust the servo travel setting, just like you would for your KSTs. The nice thing...they make hidden linkages a breeze. The whole seevo movement would stay right in the wing..no slots, just a pass through for the linkages.

 

[Konrad]

I’m well aware of the linear actuators and have been for a long time. Not aware that they aren’t susceptible to wear. Also don’t see any advantage for the dual output we see in the old configuration, other than balanced load on the rack. But I only saw this used in the old days when we used a single servo to drive both ailerons, be that linear or rotary output servos.
(Note that with the rotary configuration of the surface horn the linear servo gave us a rather non-linear control response.Ok, is you wanted expo they gave you that. This and the limited geometry flexibility relegated the linear servo to history as a motivator for our control surfaces.)

 

[Txmustangflyer]

There is a difference between their linear acruators and linear servos.

Their linear servo mivement is the same principle as a standard servo, their movement is proportional to radio inputs. The actuators are an on/off, good for gear doors, canopies, etc. When switched they will move full travel...period, until that travel hits the limiter switch, if used. As far as wear, I'm going by posts made from folks running them for some time. Take a look at attached photo. Nit much room for gears in there. I've not bought any yet, but my guess is a screw drive, driven direct off the servomotor. Without taking one apart, hard to tell.


Yes, it would be possible to use on
E of their linear servos on each aileron, just be advised, they don't move as fast as a standard servo..theres a bit more delay from what I understand. Good for rudder or flaps in non 3d planes where fast travel speed in the rudder isn't really necessary, but very good for flaps. As long as both flap linkages are same exact length, then setting the servo throws through the orogramming creates the exact same setup on both wings. Same goes for things like gear doors, etc.

On your 3m gliders, I could see using one to decrease the pushrod length from servo to rudder, for instance, with obvious benefits. You can get the servo much cliser to the tail surfaces, inside boom, cutting the pushrod length possibly as much as 1/3rd. Less flex in the rod, more precise rudder.

Lots if possible applications for their linear servos. I just wouldn't use them for ailerons or elevator control where I may not have a want for rapid movement, but may need that rapid movement.

I'd look at the specs on them. You might be surprised. Lots of scaled out warbird builders are using them regularly, even on ailerons, to make keeping the linkages hidden that much easier, especially on competition scale warbirds, part of those competitions are scale flights. They will go toe to toe with a hitech hv digital as far as torque, throw, and speed. Dunno how they stack up against KSTs, but their use is becoming, slowly, more widespread.