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Original KP-4 Kraft Propo: A Vintage R/C Xmas read, enjoy!

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Original KP-4 Kraft Propo: A Vintage R/C Xmas read, enjoy!

Old 12-21-2015, 12:45 PM
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jaymen
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Default Original KP-4 Kraft Propo: A Vintage R/C Xmas read, enjoy!

I received one of these from Bob in Orlando several years ago, and we would up deciding it would be far easier to replace the main board with a more modern one from another radio, as we could only get a modern receiver to follow the first two channels, and it would sometimes skip or jump channels as well, or quit altogether. Here is a write-up I did based on the radio and our experiences with it, plus my recollections of discussion I had with Don Mathes back in the 1980s when he worked with us a World of Robots:

The first KP-4 proportional by Kraft.

This radio, although it was not advertised, the KP-4 was Kraft’s first commercially available digital proportional radio. Compared to the Kraft-Pullen proportional radio that was in development around 1963, it was much simpler in that it used far fewer components. In addition, it was a true 4- channel full house system offering proportional control on all channels. The original version of this radio used quite a different arrangement in both the transmitter encoder and receiver decoder design, and as such, neither are compatible with the later KP-4B and KP-6B that followed. This was because the encoder used a self-triggering string of one shots, with no master oscillator/ multivibrator to control the frame timing. Instead, there was a start button on the front of the transmitter which when depressed would fire the first channel one shot which then in turn fired the second one shot and so on until all the one shots had fired. The last one shot would then re-trigger the first one and the cycle was then repeated. The pulse frame consisted of only four pulses instead of five, which is odd because conventional PPM digital proportional pulse frames consist of one pulse per channel plus an extra “sync” pulse at the beginning of the frame as a timing signal. Now how did Kraft then get four functions and use one less pulse than normally required? Well, there is normally a pause of about 6-10 milliseconds after the pulses, called the sync pause, that allows time for all the logic to reset once the channel pulses have been processed, this is done so the encoder and decoder can then reset and send another frame of information. What Kraft cleverly did was to vary the time of the sync pause and use it to convey a 4[SUP]th[/SUP] channel of information. The other trick was that by making the encoder self-triggering, it eliminated two transistors needed for a master multivibrator circuit to set up the encoder timing. The last trick was done as a cost saving measure.

Sound great, and very ingenious, doesn’t it? Well guess what, it was, in theory, but not in practice. One issue was drift, because without a multivibrator to act as an accurate master timing clock, the encoder lacked accuracy, therefore any small variations in each of the channels one shots were cumulative, causing some interaction, and drift. In addition, without a master timing clock that forces the start of each pulse frame, the encoder could, and would sometimes not self-trigger and stop, or “lock up” and quit sending pulses. This could, and did crash many planes. In theory, the encoder should have self-started when turned on, but this was not always the case, and hence the reason for Kraft putting a small “start’” push button on the transmitter face. If the transmitter quit, and if the pilot had fast reactions, he could possibly hit the start button in time to avoid a crash. On the receiving end, the decoder had an odd arrangement that allowed it to look at the variable synch pause and convert it to a pulse to drive the throttle servo.

Kraft quickly abandoned this design, and came up with a second generation version but added two more channels and called it the KP-6. Early Kraft price sheets reflect that KP-4 airborne equipment is not compatible with either the KP-6, or later KP-4B and KP-6B systems. Apparently however, they had produced enough of the original KP-4 systems to continue offering support in the form or replacement transmitters, receivers and servos. Once the KP-4B came out, it had a new circuit board in the transmitter that was similar to the KP-6 in that is used a master clock circuit. It must be pointed out however, that even the second “B” versions were still fairy crude in their design as Phil was still trying to use as few components as possible to keep the cost down. The KP-4B and 6B both used a single uni-junction transistor in place of a two transistor mutlivibrator for the master clock. This was common of early digital sets such as the Digitrio designed by Ed Thompson, which also utilized a uni junction master clock. To eliminate neutral drift and improve the linear response of the system, it became necessary to implement a two transistor multivibrator circuit using precision film timing capacitors for the master clock, and this then became a stand design feature of all digital proportional radios produced from about 1966 onwards.

Other than the obvious cost cutting measures employed by Phil Kraft which was based on a notorious technique called Muntzing, (remove as many parts as you can before it quits working), there was really no good reason that justified continued production of the original KP-4 design, as it proved problematic and hurt Kraft’s reputation for reliability. This probably explains the reason for them not being advertised, or sent out for review by the magazines either. At the Time, Phil had not only Jerry Pullen, but Don Mathes working on the proportional radio design, and Don’s experiences with his failed Digicon project had much to do with this. This is little doubt that he advised Phil to proceed cautiously and not do any press releases before they fully tested the new radio. One can also imaging that Don probably had his doubts and objections over the Muntzing of the KP-4, especially since his Digicon design had already proven the reliability and efficacy of a solid master oscillator encoder design. This is the typical age old battle between the engineers and the sales department which is waged over what is ideal, and what is practical. Don used to recount to us about how he would become frustrated by Phil’s continual Muntzing of his prototypes and designs.

What is quite interesting to ponder is why Kraft spent over two years of effort trying to develop an alternative technology to digital proportional after it came out. My own assessment is that Phil was driven by the desire to produce his radio at the lowest cost to make the best profit margin, and help it outsell other brands due to a lower price point, that, and the lack of a consensus at the time as to what design would prove to become the industry standard. Add to this the fact that Don and Phil were keenly aware of what had happened with the Digicon, and therefore were proceeding cautiously before going to the press with the KP-4. Inspite of having produced a significant number of these first proportional radios,Phil was able to overcome the setbacks with the first KP-4 for several reasons: First off, Phil Kraft was a well-established and respected R/C manufacturer; the KP-4 was not his only product and he was well entrenched in building successful single and multichannel equipment that had a very good reputation for reliability. Secondly, he did not advertise the first KP-4, even though he built and sold quite a few. He shrewdly did what today is known as a "soft" product release. Third, he had follow-up designs in the KP-6 and "B" series that were much more reliable by comparison. One must also keep in mind that virtually every digital proportional radio that came out between 1963 and 1965 had its share of issues as each one had its own quirks due them all being new designs using newly developed components as well. It was the accepted "norm" that you had to have three proportional radios: one in the plane, one in the repair shop, and one in the mail on its way to or from the shop! Another clue to the cantankerous nature of the equipment in those days was the practice of test flying most, if not every radio system. A little known fact is that the Ugly Stick started life as a test bed for radios systems. Phil had dozens of Ugli Stick planes made, and then he recruited a crew of pilots to use these plane to test his radios. In exchange, they got free planes, fuel, props and a free radio system as well.

Phil got the idea for the Ugli Stick from observing Zel Ritchies specially designed plane he used for test flying his Space Control 4 channel analog systems.

Last edited by jaymen; 12-21-2015 at 01:24 PM.
Old 12-21-2015, 01:47 PM
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Great history lesson, Jay. Thank you for that.

Dick
Old 12-21-2015, 07:20 PM
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Good read! I got into RC just after that time period in history and living on a farm in the middle of the country, any info that came my way was fairly stale and outdated. I could only afford simple or outdated equipment (read that highly unreliable) until about 1970 and I started going to contests shortly after that. Meeting people at contests, there were always stories about the various equipments we were using and enjoying. So many stories have surfaced over the years and ones like yours above further fill in my curiosity gaps. Thanks!
Old 12-23-2015, 02:34 AM
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Interesting read. I had one of Frank Hoover's F&M Digital 5 radios back around '65, suffered a bit from glitches but on the whole worked well. Frank came up with the idea of spike off to aid agc response in the Rx, a problem the original Digicon suffered from.
Old 12-23-2015, 07:52 PM
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Was it less expensive than the prototype "Pullen" in 1963?
http://www.rchalloffame.org/Exhibits...t36/index.html
Old 12-24-2015, 05:00 AM
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I still have my fully operational KP-5c. It was used and was my first radio and never failed me. Used it until a Futaba 7FG replaced it. Still have it with a gold stickered AM module in it.

Merry Christmas to All
Old 01-08-2016, 04:00 AM
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51.50
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I started working for Kraft Systems in the summer of 1964 as the shipping clerk. Because I had electronics in my background, I was promoted to the single channel radios and then to the reed units. The first time I saw the future Ugly Stick, it was literally a square frame test plane. Phil called the " Box Fli". It was Al Bowman that suggested Phil add the changes that became the ugly stick. All Bowman always gave his honest opinion. He didn't seem concerned if Phil liked it or not.
In reference to the KP-6, it seemed to work well but the double deck receiver as huge. I remember during development of the KP-4, a new idea was assembled and bench tested. Phil would close the shop and
all the employees would get in vehicles and follow to the Whittier Narrows airfield and watch Phil test fly the newest version of Kraft Proportional. We moved to a larger facility where we began making the PCS 5 along with the Kraft line. Soon another factory was opened in East Los Angeles. Cliff Wierick promoted the PCS-5, Kraft electronics with Bonner sticks for $299. The PCS-5 sold well. I went to work for Micro Avionics in 1968. After Micro Avionics closed, I worked at Orbit Electronics repairing the Micro Avionics equipment. I believe or I should say in my opinion the last version of the Micro Avionics the XL IC was the same RF circuit with the logic handled by new ( at the time) integrated circuits (chips). The new XL IC design should have included better noise rejection. It did not.

Last edited by 51.50; 01-12-2016 at 05:25 PM. Reason: spelling
Old 01-08-2016, 07:14 AM
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The PCS-5 at $299 was the death knell for some of the other proportional manufacturers, especially the analog systems.
Old 01-12-2016, 05:33 PM
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51.50
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To ukengineman, While working at Kraft in the Lee ave plant I became acquainted with Maurice Franklin. His brother Geoff Franklin published or worked for an RC magazine in England. Did you know-them? Maurice was a technician for Kraft Systems
Old 01-12-2016, 10:29 PM
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I knew Maurice. Met him about 40 years ago at the Ocean Side plant. He worked in the service department.
Old 01-13-2016, 02:20 AM
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Originally Posted by 51.50 View Post
To ukengineman, While working at Kraft in the Lee ave plant I became acquainted with Maurice Franklin. His brother Geoff Franklin published or worked for an RC magazine in England. Did you know-them? Maurice was a technician for Kraft Systems
Although I didn't know Geoff and Maurice Franklin personally, they were well known personalities to the UK R/C community back in the 1960's. If I remember correctly Geoff ran a model shop and often appeared in the pages of RCM&E. I don't believe they are with us now.

Added note: Geoff Franklin's model shop was in Leicester UK, he also formed the LARKS club

Last edited by ukengineman; 01-14-2016 at 02:32 AM. Reason: more info
Old 01-17-2016, 10:51 AM
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Jay,
I always marveled at how well the Kraft System worked with so few parts. Your perspective is very interesting to me. In the late '60s and early '70s Futaba didn't work very weill. It is my opinion their first good radio was a basic copy of the Kraft at that time. I always thought they picked it because of the lower cost to produce. E.K, Proline and Royal were too expensive to copy.
Old 01-17-2016, 06:17 PM
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51.50
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Ukengineman, Maurice designed a pattern plane in the time period before Kraft moved to Vista.
Were you aware of it? I'm struggling with my memory but I think it may have featured in RC Modeler. If I can locate to plans, I would like to build one. I remember the fuselage shape was similar to a P40.
Old 01-18-2016, 02:43 AM
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I recall a plan published in RCM&E by Maurice Franklin around that time. I think it was supposed to be good for knife edge flight. I'll take a look through my old RCM&E's and get back again.
Old 01-19-2016, 02:30 PM
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Originally Posted by ukengineman View Post
I recall a plan published in RCM&E by Maurice Franklin around that time. I think it was supposed to be good for knife edge flight. I'll take a look through my old RCM&E's and get back again.
OK, I have found the article by Maurice Franklin in the Aug 1967 issue of RCM&E. The model is called Henchman and was said to be a pattern plane that was good for knife edge flight. There is an accompanying article about knife edge flight. Only a small size plan is shown although it is dimensioned so it should not be a problem to redraw full size or perhaps get a copy shop to enlarge it. A scan of the plan is attached. Interestingly in the Dec issue of RCM&E Kraft's Bar-Fli is featured and Phil makes reference to the influence of the Franklin design. Not sure if this is the model you were thinking of but hope it is of interest.
Alan
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Old 01-19-2016, 04:12 PM
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5150, hah, we are all crazy about model airplanes are we not?

The Micro Avionics XL-IC was plagued with a component problem that was not design related. Sadly, Bob Novak had done his homework, but alas, Motorola had not. Their first series of IC chips, the JK flip flops with gold pins, had a big problem: the epoxy they used for the black body was hydgroscopic, meaning it absorbed moisture and humidity from the air and eventually caused the chip inside to become eraatic in operation. The failure mode included the channels hopping/jumping positions, like rudder becoming throttle and other such nonesense. Aparently Motorola released quite a few of these chips into the market before they discovered the problem, but failed to recall them. This is what really pissed off guys like Novak, and Dunham, because Motorola knew about the problem and said nothing. If you remember Big John Eliot, he took Zel Ritchies place as an Orbit factory test pilot, and also they had him repairing the old reed sets, which he was good at doing. Big John was tasked with test flying the XL-IC series radios and discovered the problem. He was a good enough pilot to realize it had jumped channels, so he flipped the transmitter upside down and backwards, and was able to land the plane in one one piece and leave it turned on until he got it back to the factory for Novak and Dunham to look it over. Tha is how they pin pointed the Motorola flip flops as the culprit of all their woes.

Last edited by jaymen; 01-19-2016 at 04:17 PM.
Old 01-21-2016, 01:46 AM
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Originally Posted by ukengineman View Post
OK, I have found the article by Maurice Franklin in the Aug 1967 issue of RCM&E. The model is called Henchman and was said to be a pattern plane that was good for knife edge flight. There is an accompanying article about knife edge flight. Only a small size plan is shown although it is dimensioned so it should not be a problem to redraw full size or perhaps get a copy shop to enlarge it. A scan of the plan is attached. Interestingly in the Dec issue of RCM&E Kraft's Bar-Fli is featured and Phil makes reference to the influence of the Franklin design. Not sure if this is the model you were thinking of but hope it is of interest.
Alan
It was also published in Model Airplane News. http://www.outerzone.co.uk/plan_details.asp?ID=6942
Old 01-21-2016, 08:44 AM
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Yes, that is the plane I was thinking about. Thanks for the info. a side by side comparison of the Henchman and Bar-Fli would be interesting.
Old 01-21-2016, 08:59 AM
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Out of pure curiosity, I would like any info on the time period when the XL IC was put into production and the closing of Micro Avionics if you remember and want to share. I was working at Micro Avionics when Bob Novak first came to work there.

Last edited by 51.50; 01-21-2016 at 05:30 PM. Reason: detail
Old 01-28-2016, 01:33 PM
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Jay,
I have been trying to contact you by email, phone and private message with no reply.
Could you tell me what is going on with my Controlaire 10-channel reed receiver?
Thanks in advance.
Jean-Marie Piednoir.

Last edited by JMP_blackfoot; 01-29-2016 at 09:22 PM.

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