$300 homebrew wing levelling system

With the summer thermals upon us, and not being able to scratch my nose
without having my small homebuilt tossed off course got me to thinking
about how to build a low cost wing leveller.

A small servo tab mounted out on the aileron, controlled by a jumbo
sized R/C servo would probably work fine. If the tab was sized fairly
small, even if the servo went nuts, the pilot could easily overpower
it.

The servo would be controlled by a rate gyro that is also used in model
airplanes and helicopters to provide the stabilizing function.

The overall system would be controlled by a simple pulse-width
modulator using a 555 chip. A small amount of trim adjustment would be
provided.

Operation would be simple: turn on the system and adjust the pulse
width trim knob to get the wings level. Sit back and scratch your
nose, take a pee, eat a sandwich.

This simple system could be put together for under $300. Any thoughts
on how it might work?

tom

wrote:
With the summer thermals upon us, and not being able to scratch my nose
without having my small homebuilt tossed off course got me to thinking
about how to build a low cost wing leveller.

A small servo tab mounted out on the aileron, controlled by a jumbo
sized R/C servo would probably work fine. If the tab was sized fairly
small, even if the servo went nuts, the pilot could easily overpower
it.

The servo would be controlled by a rate gyro that is also used in model
airplanes and helicopters to provide the stabilizing function.

The overall system would be controlled by a simple pulse-width
modulator using a 555 chip. A small amount of trim adjustment would be
provided.

Operation would be simple: turn on the system and adjust the pulse
width trim knob to get the wings level. Sit back and scratch your
nose, take a pee, eat a sandwich.

This simple system could be put together for under $300. Any thoughts
on how it might work?

tom

http://hometown.aol.com/ccady/eztrim2.htm

--
John Kimmel

remove x

"He's dead, Jim."

Interesting site, but aimed at altitude hold. My idea is for a wing
leveller.
tom

http://hometown.aol.com/ccady/eztrim2.htm

John Kimmel

wrote

This simple system could be put together for under $300. Any thoughts
on how it might work?

Sounds like you are on the right track. One thing I would think about
adding, is a way to automatically correct for the rate gyro's drift.
Perhaps a static port out on each wingtip, and a differential pressure
comparison? It could just do a correction based on a timer every few
minutes, perhaps.
--
Jim in NC

Morgans wrote:
wrote

This simple system could be put together for under $300. Any thoughts
on how it might work?

Sounds like you are on the right track. One thing I would think about
adding, is a way to automatically correct for the rate gyro's drift.

Worst case for most of those RC gyros (designed for RC helicopters,
etc.) is about 3 degrees per second. Most of our airplanes will
naturally STAY level better than that. Better gyros are available, of
course, but the price goes up... A good Crossbow 3-axis gyro is $3K or
above.

What most of the cheapo levelers for homebuilts do is add temperature
compensation, then have a microprocessor assume that most of the flight
is straight and level anyway - recalibrates every few seconds. Note
that this system is not foolproof (one reason why it is not certified)
and suffers the same "self erection" problem as does a conventional AH.
Namely, if you hold the plane in a turn for a while, the turn becomes
straight and level, and "straight and level" keeps the plane turning.
{:(

"jmk" wrote

Worst case for most of those RC gyros (designed for RC helicopters,
etc.) is about 3 degrees per second.

Wow, I didn't know that they sucked THAT bad! g
--
Jim in NC

Morgans wrote:
"jmk" wrote

Worst case for most of those RC gyros (designed for RC helicopters,
etc.) is about 3 degrees per second.

Wow, I didn't know that they sucked THAT bad! g

Remember... that's *worst case* according to their spec.

They are based on the cheap MEMS solid state chips that are so
incredibly cheap because most modern cars have a anywhere from 4 to 20
of them. Usually a couple on each wheel, and another on each wheel
that steers. They compensate for the GPS shadowing that is otherwise
unacceptable on a moving map when driving in the city or under trees
(especially if it's been raining). They are only expected (in this
application) to show the basic turn direction for a couple of seconds
until the GPS can "catch up."

There more critical function is anti-skid, ride quality, and braking
functions - again, while the application may be critical, the exact
numbers aren't.

In a reasonably constant temperature environment, with some minimal
compensation from a processor, they should do MUCH better.

However, for something like replacing the AH, they are a LONG way from
being ready for prime time - at least without major enhancement. [We
did some rather fascinating experiments with "shake and bake" when the
first uncertified units came onto the homebuilt market. Including
putting one on a battery operated record player platter and setting the
whole thing (instrumented) in a refrigerator! After a few minutes it
showed the plane flying straight and level (DG function) as it went
round and round and round... G]

Interestingly enough, they are being used as part of the replacement
gyro for the King and Sandel HSI. The catch - like the automotive
moving map in cars, they are being updated every few seconds by the
flux gate.

"jmk" wrote in message
oups.com...

Morgans wrote:
"jmk" wrote

Worst case for most of those RC gyros (designed for RC helicopters,
etc.) is about 3 degrees per second.

Wow, I didn't know that they sucked THAT bad! g

Remember... that's *worst case* according to their spec.

They are based on the cheap MEMS solid state chips that are so
incredibly cheap because most modern cars have a anywhere from 4 to 20
of them. Usually a couple on each wheel, and another on each wheel
that steers. They compensate for the GPS shadowing that is otherwise
unacceptable on a moving map when driving in the city or under trees
(especially if it's been raining). They are only expected (in this
application) to show the basic turn direction for a couple of seconds
until the GPS can "catch up."

There more critical function is anti-skid, ride quality, and braking
functions - again, while the application may be critical, the exact
numbers aren't.

In a reasonably constant temperature environment, with some minimal
compensation from a processor, they should do MUCH better.

However, for something like replacing the AH, they are a LONG way from
being ready for prime time - at least without major enhancement. [We
did some rather fascinating experiments with "shake and bake" when the
first uncertified units came onto the homebuilt market. Including
putting one on a battery operated record player platter and setting the
whole thing (instrumented) in a refrigerator! After a few minutes it
showed the plane flying straight and level (DG function) as it went
round and round and round... G]

Interestingly enough, they are being used as part of the replacement
gyro for the King and Sandel HSI. The catch - like the automotive
moving map in cars, they are being updated every few seconds by the
flux gate.


I've been carefully watching the MEMS AHRS and IMU units for a while. The
makers claim good performance but charge high prices.

There is another way to achieve attitude sensing and that is multi-head GPS
receivers that measure carrier phase difference between the antennas. If
you combine MEMS AHRS with GPS attitude the two independent systems
complement each other such that the AHRS provides "coast-through" attitude
during GPS dropouts. It's not cheap but 0.1 degree resolution is possible.

Google "CSI Wireless". No connection.

bildan

jmk wrote:
Morgans wrote:
wrote

This simple system could be put together for under $300. Any thoughts
on how it might work?

Sounds like you are on the right track. One thing I would think about
adding, is a way to automatically correct for the rate gyro's drift.

Worst case for most of those RC gyros (designed for RC helicopters,
etc.) is about 3 degrees per second. Most of our airplanes will
naturally STAY level better than that. Better gyros are available, of
course, but the price goes up... A good Crossbow 3-axis gyro is $3K or
above.

A $30 analog devices mems gyro drift is about 70 degrees/hour with
temperature calibration, straight out the box they are pretty lousy
(and I think Crossbow uses the analog devices chips but calibrates the
crap out of them). RC helicopters use the older style piezo gyro's.

It will work. I know because I have had one on my Tango 2 for
about a year. I didn't want to build the mechanism to move the trim
tab on the already moving aileron, and then have to rebalance the whole
works. Since the aileron moves a tiny amount for roll control, I
figured a large trim tab on the wing tip might work. I sawed off the
trailing edge of one wingtip with the same chord as the aileron and put
on a simple hinge. Not pretty, but its a prototype. I used a $78 R/C
servo, about 2 1/2 inch square, plenty of force, rigged it to give
about 20 degrees up and down. I picked that servo because that's what
Craig Sellars, PCFlight Systems, had laying around for free. He
initially gave me just a knob to manually control the trim tab to test
the concept. I could start a slow roll either direction and reverse it
at will. At full deflection I could easily overpower the trim tab with
the aileron. Runaway trim, not an issue.
Craig then hooked up one of his solid state AHRS units to the
servo to try wing leveling. First flight, worked great. The AHRS
senses turn rate, so it will attempt to correct for bank and yaw. When
I trim the ball to the center, the wings stay level and the heading
remains steady. If I want to turn a little, I just turn, roll out and
let the AHRS figure out what happened. Heading hold and course
tracking will be simple, requiring only a signal from a GPS, VOR or
magnetometer.
For a low budget system it seems like any system that can control
an R/C helicopter should be able to handle a simple wing leveler.
wrote:
With the summer thermals upon us, and not being able to scratch my nose
without having my small homebuilt tossed off course got me to thinking
about how to build a low cost wing leveller.

A small servo tab mounted out on the aileron, controlled by a jumbo
sized R/C servo would probably work fine. If the tab was sized fairly
small, even if the servo went nuts, the pilot could easily overpower
it.

The servo would be controlled by a rate gyro that is also used in model
airplanes and helicopters to provide the stabilizing function.

The overall system would be controlled by a simple pulse-width
modulator using a 555 chip. A small amount of trim adjustment would be
provided.

Operation would be simple: turn on the system and adjust the pulse
width trim knob to get the wings level. Sit back and scratch your
nose, take a pee, eat a sandwich.

This simple system could be put together for under $300. Any thoughts
on how it might work?

tom