mrlogdog

My Feedback: (61)

does anyone know if the old four prong kraft servo can be converted to futaba. i have an old set of kraft retract with just two wires but the plug has four prongs.

skypupmut

you could with adapter cables and center taped batt pack,
but you will be getting slow not very powerfull servos with very thin gears
and no parts available to repair, new sport servos will serve you better
at lower price and your will probably have to recenter the servos
I do not know about the retracts, never got those

mrlogdog

My Feedback: (61)

it is the retracts i'm more interested in. seems there aren't any servos to say on the retracts. they have built in motors. i can make them work with a battery. just hoping to be able to convert them to standar plug. thanks for your imput

skypupmut

I would have to check old magazines, I beleive they were operated from a switch that was operated by a servo not sure anymore
that was 35- 40 years ago LOL

RCDENT

My Feedback: (2)

The retracts operated from an "amplifier" that was included in the set. It simply plugged into the receiver like a servo, with wires that went to the individual units. It worked fine from my Futaba 9VAP years ago. Lacking the amp, you would have to rig up some kind of arrangement with micro switches and a conventional servo. The nosegear must be mounted in a foam tape-lined box or the engine vibration will kill the electric motor. Overall, a very reliable system until fiberglass fuses and tuned pipes became the rage in pattern in the 80's. The vibration was then too much for the nose units. They used the same motors as one of the old Kraft servos, but I don't remember which one.

8178

My Feedback: (17)

I remember seeing the small Kraft amp/control that plugged into he Kraft receiver and that controlled the retracts.

From looking at your plug it looks like someone added RF chokes in the leads but tied the wires together?? RF chokes are usually located at the motor not out in the power leads. That does not look like the work of Kraft. 70s vintage electric retracts/retract servos usually used limit switches inside to stop the retract motor when the gear reaches the full up or down position. When limit switches are used, three or more wires are needed to each retract unit and diodes are used inside the retract servo or unit to prevent feed back between the limit switched in either retract unit.

I’ve attached a retract servo schematic that was published in the June 1971 RCM along with one of my RC pattern designs. I used a DPDT slide switch for control that was moved by a servo on my retract switch on my TX. I used forward biased HEP52 transistors for the feedback protection rather than diodes to reduce the voltage loss and the limit switches replace the potentiometers in my retract servos. A separate battery pack was used to power the retract servos to avoid any problems with flight pack battery if a gear jammed. Goldberg came out with a retract servo that worked just like my system a few years after my RCM article.

If you cannot find the Kraft wiring info you may need to take of the units apart and figure out how they are wired inside and how the limit switches work. It is possible that Kraft put a limit switch on each side of the motor and then used one red/back wire set for up and the other red/black wire set for down. The extra wiring provides a separate up and down voltage path. In your case someone has tied the wires together so you only have two wires to the react. I don’t understand how it can work that way.

The fourth image is a simplified view of what the wiring might look like inside the Kraft retract unit using four wires and two limit switches.

The fifth image is how a DPDT switch could be wired to make the retracts work if they are setup like the fourth image.

mrlogdog

My Feedback: (61)

8178,
Thanks for the info. there are only two wires to each retract. i was able to control the up and down of the motors by switching the pos and neg around , one way for down the other for up. the motors in the housing stop on their own, so i'm guessing there is a limit switch on both sides. thanks for the schematics

8178

My Feedback: (17)

The picture of your plug with four wires confused me. Is that single plug in your picture with four wires used for both retracts, two wires each? The limit switches inside the Kraft retracts must have a diodes across them to make them work with just two wires. If that is the case you are good to go with the simple DPDT switch below .

HighPlains

My Feedback: (1)

Most likely there is a diode across each limit switch to allow the current to reverse the motor position after the limit switch stops the motor. That only requires two wires to each retract.

8178

My Feedback: (17)

As I said, I expect that is the case too. When I designed my retract system in 1969 I used standard World Engines S4A servos with the electronics removed and had to use the feed back pot mechanics to make my 180 degree limit switch. I was limited to one common connection on the limit switch so I had to use three wires to each servo. Later on WE started making servo mechanics that were geared down for retract use that were a lot better than the S4A. After using the 1969 system for years a friend and I deigned a controller that plugged directly into my Kraft receiver and monitored my retract channel to control the retract servos. The controller worked pretty neat, eliminated one servo and used a separate battery pack to power the retract servos. When I did this system I used printed circuit board and etched the limit switch tracks for the limit switch. I still have the system that was last used in a P51 in 1975 with a retracting tail wheel. When Sonic Systems came out with air cylinders and then later on Rom-Air developed their retracts and then Spring Air, my retract servos became obsolete.

mrlogdog

My Feedback: (61)

two wires to each retract. and basically all the reds are tied together and all the blacks too. I did fiddle around with it and found that by reversing the + and - the retract either go up or down. they stop by themselfs. i think a dpdt switch will work in this applications
thanks to everyone who helped

8178

My Feedback: (17)

You’re welcome! Nothing’s more fun than old RC stuff. At one time Radio Shack was a good source for small slide type DPDT switches but I’m not sure if they stock that stuff anymore.

Mike Denest

My Feedback: (1)

There's a difference between the Kraft and Multicon units. Since both use an amplifier to actuate the gear, the Kraft units were compatible with the later three wire system, using 4.8V motors. The Multicon units were based on the four wire feedback circuit used on the Kraft Gold Medal series and Sport Series. These used the 2.4V motors to operate the gear, requiring a center tap from the battery for + and - voltage to move the gear.

rcacro

You can use the circuit board from any old servo to drive the 2 wire retracts. Just connect the retract wires to same place the servo motor leads were connected to. Replace the servo feedback pot with a small 5k pot set to approx center. Retract switch will then cause the voltage to the retract servo to reverse the same way you did reversing the connections to a battery. You can drive at least 2 retract servos with the same servo board. I had all 3 hooked to the same PCB in my pattern ship about 20 years ago.

John

doxilia

My Feedback: (3)

Logdog,

everything that is concluded by others above is correct. I've lately been involved in a little research on what became know as the Kraft Multicons (only one company as Kraft must have bought Multicon, if a company with that name existed - not sure. Any thoughts Mike Denest?).

The early retracts used 2.4V motors which actually don't work very well at 2.4V (2 x 1.2V cells). Today a preferable source would be a single A123 3.3V cell. These retracts used red/white wiring and could be run with either center tap flight pack leads and a switch as described above or via a 4 lead amplifier which would connect to specific receivers of the time. The later retracts ran at 4.8V and were intended to be powered by the standard power source for the flight pack - no center tap. These units had red/black wiring.

I've attached photos of the instructions that came with the units for reference. You'll see that two different types of amps are discussed on the last page. One was presumably for the older 2.4V units (4 leads - top left) while the other was for the newer 4.8V units (3 leads - exploded view). I've also included some photos of the retract units and leads - the last one being a 2-wire Y-harness for the 2.4V units to be used with an amplifier.

The wire that you show is actually the Y-harness that joins the 2-wire mains for exit from the wings. Although not yet confirmed, I suspect there are 4 wires in order to provide current to either the left-most 2 pins or the right-most 2 pins with the wires being pole reversed at the Y-junction. This allowed +- (reverse) voltage to be applied to the retract for actuation just as you describe. I also suspect that this was only necessary for systems installed with a switch but unnecessary for systems using an amp as the latter probably took care of voltage reversal. In this case probably only two of the four pins were used by the amp. As I'd rather not remove the heat shrink from Y-lead to verify my suspicions, I can't confirm. There will be other ways to confirm though once the available amplifier situation is sorted out.

This is an old thread so perhaps interest in this has waned. I hope not.

David.

P.S. I'll have to rethink this when I have some amps to clear up and doubts or speculation.

P.S.2. I'd like to thank Mike (8178) as he, as usual, offers insightful and helpful commentary.

doxilia

My Feedback: (3)

BTW,

I'm not sure why chokes were added to your mains Y-harness but as Mike (8178) says, it is probably not the work of Kraft judging from the standard Y-harness (no chokes) that comes with the units. It looks like someone must have modified them to suit their needs but I suspect (to repeat myself) that the junction on the standard harness is not red/red - black/black as in your harness. There would be little point in using a 4 pin plug if that were the case. The only reason I can think of for why Kraft would have used a 4 pin plug on equivalent wiring to yours would be to standardize all AMP and/or RX connections to 4 pin - which is also possible.

David.

Deadstik

My Feedback: (8)

Thanks to this thread I realize now why I've got retracts with different amplifier wiring. Might have just saved me a set of gear so Thanks! I love the Kraft electrics and used them in almost every pattern plane I flew in the late 70's and early 80's till I switched over to MKs. Have to admit putting in the electrics was MUCH easier... but as 8178 said... the nose gear just didn't like all the vibration...I'm going to look into trying to find some NIB kraft servos to get some motors for the retracts I have left.


Dan
Carolina Custom Aircraft

doxilia

My Feedback: (3)

Dan,

I couldn't agree more... this thread has helped solve some unanswered questions I had.

BTW, If you should come across any of those Kraft servos, I sure could use a triplet to replace (if not now, eventually) the 2.4V motors in the units I have. I would prefer to use 4.8V motors, or better yet, 6.0V motors (I guess that would allow modern servo motors to be used?) so that I could run the retracts off a flight pack (I like to use regulated 2S A123's or Lipo's).

Cheers, David.

Deadstik

My Feedback: (8)

Doxilla,

So the Red/White wired retracts are the 2.4 volt motors and the Red/Black wired retracts are the 4.8 volt motors? I just want to be sure before I start doing some "replacements". Do you have an idea as to what year/servo type switched over to the 4.8 volt motors? I am very familiar with the -14 and -15 servos but I haven't had a Kraft radio that ran off of the center tapped pack. I'm guessing that means that all of the 14 and 15 type servos that I used were the 4.8 volt motor. If you could confirm I would appreciate it...

thanks,

Dan
Carolina Custom Aircraft

doxilia

My Feedback: (3)

Dan,

The motor voltage switch date? That is a good question which I don't have an answer for..., yet. I'm going to see if I can get a clearer picture on when this may have happened. I would imagine that many a Kraft radio aficionado might have a good idea as to when Kraft switched from 4 pin to 3 pin radio's (I'd think somewhere in the '72 to '76 time frame). I believe this might have coincided with the motor voltage switch in servos and hence in the Multicons.

Regarding the wiring, that is correct. Red/White 2.4V, Red/Black 4.8V. I think in the mid '70's the convention in electronics switched from using white to black for ground (looked at another way, negative polarity) wiring and Kraft followed the trend. Before doing any swap outs of your motors, I would be inclined to test them out first with 2, 3 and 4 cell packs in that order. If you have 2.4V units, you'll probably find them erratic with 2 cells but much better on 3. For the 4.8V units, I'm not sure how much they can be over-driven but I would think 5.2-5.4V might be OK. A down-regulated 6.6V-7.2V pack might work nicely. Then again, you may be already in the know of all of this. If so, please do shed more light on the subject.

Here's a question you may be able to answer regarding the amps. We've established the color coding for the motor voltage. I have 2.4V units but I'm unfamiliar with how the gear should be connected to the amps. The first two photos show two amps - the first 4-lead, the other 3-lead. I assume that the 4-lead amps were intended to be run with a separate power source (either 2S pack or center tap) rather than through the RX in order to avoid the possibility of draining the flight pack (if using a separate 2S pack) in the event of a stuck gear. Based on the wire color coding here's how I think the gear is to be connected to the amps:

4-lead (based on color coding assumptions)

[ul][*] Red/White 2-wire (long) - Nose gear[*] Red/White/White/Red 4-wire - Mains Y-harness[*] Red/White/Black/Orange 4-wire (Female) - 2.4-3.0V Battery[*] Red/White/Black/Orange 4-wire (Male) - Receiver
[/ul]

3-lead (based on Kraft exploded view on page 4)

[ul][*] Red/White 2-wire (long) - Nose gear[*] Red/White/Black/Orange 4-wire (Female) - Mains Y-harness[*] Red/White/Black/Orange 4-wire (Male) - Receiver
[/ul]

I feel that the 4-lead amp connections are correct but I'm not convinced of the 3-lead amp given the use of signaling/ground wires (orange/black) on the lead to the mains (according to my logic above). Further, it would mean that the amps and gear would be driven through power fed to them via the RX (I think this was done for 4.8V units). Any thoughts?

Another possibility for the 3-lead amp is:

[ul][*] Red/White 2-wire (long) - Amp Y-harness (Nose gear/Mains Y-harness) | Mains Y-harness (Left/Right mains units)[*] Red/White/Black/Orange 4-wire (Female) - 2.4-3.0V Battery[*] Red/White/Black/Orange 4-wire (Male) - Receiver
[/ul]

This would be more consistent with the 4-lead amp in terms of color coding. When I actually have the units in hand, I'm going to have a look at the internals to see if I can gleam any useful information.

There's also a DPDT switch which, actuated by a servo, could operate any trike Multicons as per Mike's (8178) schematics. BTW Mike, do you have any thoughts on this? Finally, the last photo shows a 4-lead/3-pin white amp which I have little idea about. Other than the wire color coding differences it looks very similar to the 4-lead amp. I suspect that because of the white case and the 3-pin RX/BAT connectors, this amp was intended for either Ace (+ve pulse) or Proline (-ve pulse) radio's. Which, is unclear to me.

BTW, can anyone confirm whether Futaba is still negative pulse shift and JR/Spektrum is positive pulse shift? If so, and the white amp was made for Ace, this amp should work with modern JR/Spektrum/Hitec/Airtronics TX's.

Whew! Sorry about that Dan... rather long.

David.

HighPlains

My Feedback: (1)

The Kraft Gold Medal series thru Series 71 were all 4-wire center tapped systems. I believe Series 72 was the first year they adapted the bridged servo amp.

aerowoof

you are correctabout the year the 3 wire servo was introduced

paddles1961

My Feedback: (1)

Does anyone know if there are replacement gears for the old  multicon retracts with red and white wires??

TFF

I think the gears are KPS 14 servo gears.

sidgates

My Feedback: (2)

If the retract gears are the same as KPS-14 I may have some gears.
Sid 303-757-7019