$300 homebrew wing levelling system

[[email protected]]

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

[John Kimmel]

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."

[[email protected]]

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

> http://hometown.aol.com/ccady/eztrim2.htm
>
> John Kimmel

[Morgans[_1_]]

> 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

[jmk]

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.
{:<(

[denny]

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

[Morgans[_1_]]

"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

[jmk]

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.

[Bill Daniels]

"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

[.Blueskies.]

How about putting three or so of the sensors on board and having them each check the other?


"Bill Daniels" <bildan@comcast-dot-net> wrote in message . ..
>
> "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]

Bill Daniels wrote:
> 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.

There is no question that your idea will work, and work VERY VERY well.
NASA did some experiments and the results were WAY better than a
conventional AI. Just not quite ready for the consumer market yet -
price. But definitely has the potential to become a contender.

BTW, ref: the idea of putting multiple units in a "tell me thrice"
configuration. That would help, but except for the benefit of
redundancy, doesn't gain as much as one would think. They all tend to
suffer similar problems.

What we did do, which helped quite a bit, was characterize the units
over temperature. Although the variation between units is significant
(hence the benefits you noted), and the change with temperature is
DRASTIC, for any individual unit the change with temperature tends to
be quite repeatable. This allows you to temperature compensate the
unit with a response curve fit in software. BIG help.

Still leaves the inability to differentiate slow drift from a slight
deviation from level (or straight). But then a conventional AH
(electric or vacuum) has he same problem.

[[email protected]]

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.