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Old Nov 25, 2012, 03:58 PM
Mariner BC Canada
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How Best to Stabilize

 I'm asking for your input on a good way to control roll on my 20' (6m), pedal powered hydrofoil.

Attempts to do it manually have failed.

It seems human reaction time is insufficient to accomplish the task.

The stumbling block is the buoyant bulb which produces 1/3 of the lift required to achieve "flight".

While allowing for smaller hydrofoils (less drag), it produces incredible roll instability.

One way to manage this is by flooding the bulb at low velocities eliminating buoyancy.

CO2 purging once making way restores buoyancy and can be more effectively managed by control surfaces.

Independant foil control would be the preferred method but a centre canard (as shown) may be necessary.

The servo would be slide mounted to allow ride height control as velocity increases.

This would be controlled by a mechanical surface sensing wand geared to move the servo and control rods up and down accordingly.

The use of a canard would eliminate this complexity but add more wetted surface area.

There is only 100 watts available from the prop at steady state, sustained flight, which is the objective.

No radio is used here but the electronics from your hobby may be helpful.

I would ask for your proposed solution and then perhaps some dialogue to brainstorm a best case scenario.

The only caveat I would put out there is it needs to be relatively simple, plug and play.

On my wish list would also be light weight and low power consumption.

This is a personal project only for my use, no commercial gain or profit.

Thanking you abundantly in advance.

This video may help:



HYDROFOIL -- High flying torpedo or low flying aircraft? Ray Vellinga edited video (5 min 59 sec)
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Old Nov 25, 2012, 10:08 PM
unlicensed helicopter nut
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Berkeley, California
Joined Jan 2007
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Uh, this is the electric helicopter category. Most people who view it probably haven't got a lot of experience with flying boats....
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Old Nov 26, 2012, 12:16 AM
Cranky old fart
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Germantown, WI.
Joined Oct 2007
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You could use a gyro if you had some functions that are controlled by servos. It appears the only plane effected is roll, or is this not true? If it is, it's not much involved other than a servo, gyro and power supply. Depending on how much force is required, you can gang some pretty big servos together.
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Old Nov 26, 2012, 12:32 AM
Mariner BC Canada
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Joined Feb 2012
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I have a servo up to the loading.

Roll is my only concern here.

That's it, it's that easy?

Just plug the servo into the gyro and plug the gyro into a battery?
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Old Nov 26, 2012, 03:33 AM
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Denver, CO
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Not that easy. You need to provide a center signal to the gyro. Its PWM needs to be adjustable since most electronic devices vary a little. So people use servo testers for things like this. If you have the skill a circuit could be made.
I would go for something mechanical if possible. I would put a slight pivot in the center of the wing. Dampened with rubber. With a linkage attached so that if the wing tilted, from more weight on one side, it would change the wings angle of attack to counter the tilt.
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Old Nov 26, 2012, 07:57 AM
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Germantown, WI.
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It may require something like a flight control board to provide more finite tweaking and adjusting, but they are pretty cheap. A KK2 or MultiWii FCB and a power distribution board (multiple servos) would cost about $75; that includes the gyro. I wouldn't know if there's a mechanical solution that works better.
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Old Nov 26, 2012, 10:32 AM
Complete RC Idiot Savant
The Netherlands
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I have a little bit experience with this, using two gyro's to stabilize a gunturret on a model.

For a gyro to work properly, you would need two imput signals, usually a pulse with a range of 1 till 2 millisecond, with a pulse frequency of approx 50 Hz, that represent the control imput and the gain setting.
Unfortunately you can not just use two servo-testers, because most gyro's I have tried, need the pulse to be synchronized, meaning, it insists on these pulses to arrive one after another in a "pulse-train" and therefore you need a piece of circuitry that generates first the position pulse, next the gain pulse, than repeat that sequence.

If you just connect two independent servotesters the pulses will not be in sync and the gyro will not be able to handle it, or do anything useful with it.

But i think, it is really better to build some inherent stability in the vehicle by adding some dihedral or similar. Because a gyro will never be able to keep the vehicle perfectly horizontal, and once it is out of level it will start sliding away sideways.

However I have seen video's of some scandinavian guy that made a Human Powered Hydrofoil that had a straight foil and manual roll control, maybe 10 or 15 years back, so it is very possible you don't need that stabilisation after all....

Brgds, Bert
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Old Nov 26, 2012, 01:14 PM
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Yes, to use a simple device like the servo tester, it would need a gyro that does not need a gain signal, like a Futaba GY240.
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Old Nov 26, 2012, 01:22 PM
Complete RC Idiot Savant
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Quote:
Originally Posted by Roto Rob View Post
Yes, to use a simple device like the servo tester, it would need a gyro that does not need a gain signal, like a Futaba GY240.
Most likely that will work somewhat.... but it will not stabilize, only slow down roll tendency. And probably not enough.

As far as I know, there are no heading hold gyro's without a "remote gain imput", and with a rate gyro, you cannot stabilize an indifferent object, let alone an inherent instable one.... For that you definitely need an PI(D) controller that will keep correcting until the deviation is completely compensated.

Brgds, Bert
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Old Nov 26, 2012, 01:46 PM
Cranky old fart
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Germantown, WI.
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I was thinking more of accelerometers than gyros. They are standard on a MWC flight control board. They are quite effective on my quads.
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Old Nov 26, 2012, 01:57 PM
Complete RC Idiot Savant
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Well.... on any kind of boat, you wouldn't want to use accelerometers to stabilize the boat itself.... You would be compensating for every wavelet, and that is waste of energy by creating unnecessary drag, especially on a Human Powered Hydrofoil....

Brgds, Bert
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Old Nov 26, 2012, 02:16 PM
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United States, AZ, Mesa
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Quote:
Originally Posted by Brutus1967 View Post
Well.... on any kind of boat, you wouldn't want to use accelerometers to stabilize the boat itself.... You would be compensating for every wavelet, and that is waste of energy by creating unnecessary drag, especially on a Human Powered Hydrofoil....

Brgds, Bert
Right, that's what my thinking was - active stabilization would be too active. Some kind of passive stabilizer similar to a flybar would work great though. Do we have any gyroscopic forces we can use?

What about stabilizing it like a rocket, using rollerons!

http://en.wikipedia.org/wiki/Rolleron
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Old Nov 26, 2012, 05:36 PM
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Quote:
Originally Posted by Brutus1967 View Post
Most likely that will work somewhat.... but it will not stabilize, only slow down roll tendency. And probably not enough.

As far as I know, there are no heading hold gyro's without a "remote gain imput", and with a rate gyro, you cannot stabilize an indifferent object, let alone an inherent instable one.... For that you definitely need an PI(D) controller that will keep correcting until the deviation is completely compensated.

Brgds, Bert
The GY240 is able to be set in rate or heading hold by a switch on the gyro. Most all rc helicopter gyro's are based on PID's. Some have been hacked to allow adjustment of the parameters. http://www.rcgroups.com/forums/showthread.php?t=1610075

I have built, and raced many human powered water/land vehicles, back in the early 80's. http://boulderkinetics.com
Speed usually resulted in the judges giving little points for style, etc. The fastest on the water where almost always, light weight rowing shells, powered by oars.
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Old Nov 27, 2012, 10:52 AM
Mariner BC Canada
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Joined Feb 2012
195 Posts
Thank you all for your stimulating input.

What would be the simplest solution?

A leveller, servo tester, servo and a battery?
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Old Nov 28, 2012, 06:03 PM
Mariner BC Canada
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Joined Feb 2012
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Turns out rchelicopterfun.com is a great source of information on this.

Cheers!
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