Special Exhibit:
Doig’s Ulti Multi
(Click on any of the images
on this page to see a larger version)
This is Al
Doig’s “Ulti” Multi. It was a full-house, closed-loop,
feedback, non-wiggling, multi proportional system said to
“overcome many difficulties inherent in the pioneer
proportional schemes”.
The Ulti Multi was revealed to the modeling world in May
1959.
That’s right 1959! A full year ahead of the first
commercially–available proportional, Space Control. To put
this in perspective, here’s the timeline for early
proportional.
Early Proportional Timeline
Here’s how the
historic American Modeler article looked:
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Notice that the
servos and transmitter are identical with those shown in
the May, 1959 article. The transmitter still has Al Doig’s
identification tag on top. The receiver is his 4 channel
multi version shown in the second article on the Ulti in
July, 1959. Another receiver we have is a later version
with “Ulti III” inscribed on it as part of the circuit
board. This was presumably Al Doig’s third attempt, or
generation, “Ulti” receiver.
The Ulti Multi
was never produced for sale. It was published to inspire
modelers to perfect and improve the concept. In the second
article in July, 1959, Doig said this proportional program
is in a “development stage” and “strictly experimental” but
“maybe with more hands doing the work, correcting the
mistakes, simplifying the design, and contributing new
ideas, we will soon have the ultimate in multi”.
Doig certainly succeeded in inspiring others. We suspect
most aspiring RC experts of that day were motivated by
these articles to attempt their own Ulti Multi and touch
the Third Dream of Radio Control. We have already
discovered six of the top RC engineers who did so:
Sid Gates;
Frank Kagele;
Gordon Larson;
Vernon MacNaab;
Jim Oddino; and
Carl Schwab.
Sid Gates was the head of Royal Electronics. Kagele and
Larson designed the historic Bonner Digimite and were
actually brought together by their attempt to get parts for
their Ulti Multis. Jim Oddino was a championship RC contest
pilot and author who went on to design and sell his own RC
line, S&O. Carl Schwab designed Don Brown’s Quadruplex,
the most reliable of all pioneering proportional systems.
Vernon MacNaab modeled Citizen-Ship's first attempted
proportional system after Doig's Ulti Multi. In the April,
1960 edition of American Modeler, Citizen-Ship announced
that it had extensively flight tested a single channel
feedback proportional system "quite similar to the Doig
Ulti except that relays are used to control the servos."
Please let us know if you are aware of other RC designers
who were propelled by the Ulti Multi articles.
Doig’s achievement is even more remarkable when you
consider that California RC'ers were generally hostile to
proportional. Doig mentions in the article how “California
has long been the hold out against proportional control”
but that many California reed stalwarts actually fly
“nervous proportional” by manually blipping or beeping the
controls.
As a trailblazer Doig had to wind his own torroid coils.
His article explains how to make a crude winding machine
out of sewing needles and then wrap the coils with mylar
tape. He called this process “tedious”.
For servos he expertly fashioned new cases for Bonner
“Boxcar” servo mechanisms but one inch longer to allow room
for the amplifiers. He installed linear pots he made by
heating purchased pots until they nearly melted and could
be flattened. The transmitter was made to be exactly the
size of the local Orbit 8 channel reed transmitter and was
topped with a car antenna from a nearby auto parts store.
Bonner And Doig
Doig let Bonner conduct the test flight of his Ulti in Bonner’s Smog Hog. This employed rudder, elevator and motor (no ailerons). This disastrous flight destroyed the Smog Hog but did little to cool the enthusiasm of Bonner, Doig and others over the Ulti Multi. That’s because the crash was caused by a simple, easily correctible problem. For ease of experimentation, Doig placed receiver transistors into sockets (instead of soldering them in place) and one transistor vibrated out of its socket in flight.
Bonner didn’t mind. He was thrilled just to be given the chance to fly such a “dream” radio control system. Five years later he repaid the favor. In 1964 Bonner’s 8-channel Digimite was the new dream eagerly anticipated by flyers worldwide. Prototype Digimites won the 2 top contests at the 1964 Nationals. With release of production models many months away, leading flyers begged Bonner for one of the prototypes. One man didn’t have to beg. Months before the release of production Digimites to the public, Bonner gave one of the coveted prototypes to Al Doig. It is now on display in our museum. See “Prototype Bonner Digimite”.
Additional Technical Information
By: Carl Schwab
The system was pure FDMA (Frequency Division Multiple Access). It employed up to 4 subcarriers transmitted simultaneously. Given in the article are the coil frequencies for a 2-coil discriminator for each channel and are listed here. Rudder coils were tuned to 9120Hz and 8520Hz; elevator coils were tuned to 7625 Hz and 7025; aileron coils were tuned to 11,068Hz and 10,068Hz and motor coils were tuned to 5284Hz and 5884Hz. Thus separation for rudder was 600Hz, elevator was 600Hz, aileron was 10000Hz and motor was 600Hz.
The transmitter was a tube design in the RF portion and transistor in the subcarrier circuits. Subcarrier frequency was determined by a “Twin Tee” arrangement. As much as I can determine the motor channel was not operated using a feedback servo but rather used two or three specific frequencies within the 600Hz range for either high or low motor and was switch selected. Also notice that the motor frequency range is ½ that of the aileron and comment is made “—when the low-speed motor button is depressed, no aileron movement occurs”.
Compared to analog proportional that followed, the Ulti-Multi was a straightforward, simple system. But it had limitations because of the intermodulation effects due to simultaneously transmitted tones and using hard limiting on the tone signals driving the discriminators. Also it had a weight penalty in the receiver (where it counts) in requiring 2, high quality coils for each discriminator. The AMA had just gotten approval for the 5, 27 MHz spot frequencies in addition to 27.255 MHz and it was understood that tone modulations were to be confined below 5 KHz. Clearly Doig’s system would have to be re-worked to lower the subcarrier frequencies if it were to be sold commercially on 27 MHz making the coil weight even heavier. But, nonetheless it was a definite step forward.
