SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Aug 01, 2004, 03:10 PM
Registered User
Joined Aug 2004
6 Posts
Hello, new to the forum. How do you make a coil actuator flap?

Hi,

I am new to ornithopters. I have been researching the subject for a couple of months and I have ordered a few kits.

I am also into robot fish. I saw on the forum about these actuators that are made of coils and magnets. How can you make them flapp constantly?

I understand how they work but what i do not understand is electronics and controls.

If I use one of these on a rudder (the flapping fin) of a robot fish, how would I get it to flap all the time? On a plane you turn the rc and it pushes constant on the rudder to turn the plane. I want the rudder to be the flapping fin so when I forward the speed stick to go, i want the rudder to flap, the more forward on the stick the faster the frequency of flapping.

How do I get or make a controller that can pulst the electricty to the coils to get that?

Hope you understand what I mean. Thanks for any help!
FlipperSail is offline Find More Posts by FlipperSail
Reply With Quote
Sign up now
to remove ads between posts
Old Aug 01, 2004, 05:35 PM
Sticky Shepherd
Graham Stabler's Avatar
Oxford/England
Joined May 2001
4,017 Posts
Read this

http://rcgroups.com/links/index.php?...at=232&id=4051

We don't make actuators that flap.

fish are off topic and magnetic actuators are not a good way to produce motive force.

Graham
Graham Stabler is offline Find More Posts by Graham Stabler
Reply With Quote
Old Aug 01, 2004, 06:23 PM
Registered User
Joined Aug 2004
6 Posts
Quote:
Originally Posted by Graham Stabler
Read this

http://rcgroups.com/links/index.php?...at=232&id=4051

We don't make actuators that flap.

fish are off topic and magnetic actuators are not a good way to produce motive force.

Graham
Sorry about being off topic but I meant for using this technique on flapping planes too.

Ok, I understand the force is not so strong but I would still like to try.

Would pulsating electricity to coils be similar as making a LED blink?

Thanks Graham for the link on magnetic actuators.
FlipperSail is offline Find More Posts by FlipperSail
Reply With Quote
Old Aug 02, 2004, 05:44 AM
Registered User
Seale, AL
Joined Oct 2003
644 Posts
,,,
wmueller10 is offline Find More Posts by wmueller10
Last edited by wmueller10; Nov 04, 2007 at 09:51 AM.
Reply With Quote
Old Aug 02, 2004, 10:38 AM
Registered User
chicago
Joined Jul 2003
100 Posts
I have also considered wiether a actuator-powered ornithopter would be practical. In my opinion it's not.... unless you want to build rediculously light. So lets say it's a free flight model, A coil-magnet wieght of .2g is resonable, and due to the low amperage needed, it could be solar powered! I have no idea what the solar panel would wiegh.... but hopefuly the entire ornithopter could be built below .5g. Even then I wouldn't really expect the actuator to carry that wieght..... maybe a helium body would help
indoor flyer is offline Find More Posts by indoor flyer
Reply With Quote
Old Aug 02, 2004, 11:12 AM
Registered User
Joined Sep 2003
334 Posts
Flippersail,
It would not cost much to experiment. Bit-charger RC cars can be bought for $5-$10 dollars and could be used to drive a small fish tail with the left-right actuator. That would give you an idea of the flap rate and tail size needed. Later, a pulser on the transmitter could be worked out for you if the basic idea works. One good thing about water is that its a great heat remover so the actuator could handle a lot of current and give more torque. Once you start testing, you will be the expert!
George
Plantoflap is offline Find More Posts by Plantoflap
Reply With Quote
Old Aug 02, 2004, 03:01 PM
Registered User
Joined Aug 2004
6 Posts
WMueller, Indoor flyer and Plantoflap.

I have thought alot about why magnet actuators with coils is less powerfull than an coil-magnet motor (PM electric motor).

Electric motors are made of coils and magnets just the same as a coil magnet actuator.

But I think I know why. One reason is that on a motor the coils and magnets are always very, very close to each other and so the attraction or repulsion force is the absolute strongest.

on a actuator the distance between magnet and coils are far before activation. Thus force is low initially.

I have figured out a way to get around it though.
One solution is a spherical motor but that means alot of coils and magnets.

Another solution is multiple coils, as many as in a motor, in a shrinkable string series so it acts like a muscle. Both are difficult praticaly so maybe I go for the ordinary motor.

Maybe if I take apart a small electric motor then use all the coils and magnets form the motor as actutors. Then I get the same weigth but many actuators.

The problem I still have is controling them. I still dont understand controllers and how to get a controller to make actuators flapp wings.

I like the link to thread with the manta ray , http://www.rcgroups.com/forums/show...74&page=1&pp=15, Ill get on that thread with my fin flapping. Thanks!
FlipperSail is offline Find More Posts by FlipperSail
Reply With Quote
Old Aug 02, 2004, 06:00 PM
Sticky Shepherd
Graham Stabler's Avatar
Oxford/England
Joined May 2001
4,017 Posts
There is more to actuator/motor power than the closeness of the magnet and coil. Even motors don't really like oscillating back and forth (as servo motors have to).

All you need is a variable oscillator that will periodically reverse the direction of the current through the coil. You would have to build this yourself. Search google for 555 timer and h-bridge, the 555 is a super simple oscillator, a h-bridge is 4 mosfets/transisitors that can control the current to an actuator/motor, they allow reversal. If you want full RC control then that is another step. Learning to program pics would be one way.

Why not just use a motor and a crank?

Also a small motor can be used as an actuator if it's movement is limited over a certain angle.

Graham
Graham Stabler is offline Find More Posts by Graham Stabler
Reply With Quote
Old Aug 02, 2004, 11:02 PM
Registered User
Dallas, TX
Joined Jun 2003
465 Posts
Quote:
Originally Posted by FlipperSail
I have thought alot about why magnet actuators with coils is less powerfull than an coil-magnet motor (PM electric motor).....

But I think I know why. One reason is that on a motor the coils and magnets are always very, very close to each other and so the attraction or repulsion force is the absolute strongest.
The more important reason a coil is less efficient than a motor can be summed up by Newton's First Law of Motion - "An object in motion tends to stay in motion unless acted upon by an outside force."

In a motor the opposing charge of the coils and magnets start the armature in motion. Once in motion the centrifugal force created by the spinning armature helps to keep it spinning until friction or some other force acts to slow it down.

To use a coil actuator in the manner you are proposing the magnet will have to be stopped and reversed an infinite number of times. Therefore the coil will constantly have to fight centrifugal force instead of using it to store additional power.
Hooters Driver is offline Find More Posts by Hooters Driver
Last edited by Hooters Driver; Aug 02, 2004 at 11:23 PM.
Reply With Quote
Old Aug 03, 2004, 04:40 AM
Registered User
Joined Aug 2004
6 Posts
Quote:
Originally Posted by Hooters Driver
The more important reason a coil is less efficient than a motor can be summed up by Newton's First Law of Motion - "An object in motion tends to stay in motion unless acted upon by an outside force."

In a motor the opposing charge of the coils and magnets start the armature in motion. Once in motion the centrifugal force created by the spinning armature helps to keep it spinning until friction or some other force acts to slow it down.
You are right,

But eletric motors have extreme torque at stand still. The most torque of an electric motor is from start, when there is no motion, no centrifugal force or momentum or anything. Electric cars driven by gearless and brushless direct drive with a PM are usually very fast accelerators but have limited top speed. The torque of an electric motor is highest at stand still.

An electric actuator seems to have very bad torque from "start", This I think is because of the distance of magnets and coils. But you ar right, the constant accelerating and stopping with an actuator is less efficient than the continuous circulation of an electric motor.

I will start with crank motor but I realy like the idea of getting actuators to work. The advantage i see with actuators is to "easily" vary the amplitude of flapping and to vary the oval movement of the flapping. With a crank you are kind of stuck with a fixed amplitude.


What about this:

You have a very short actuator. The coil is coiled around a short cylinder. The cylinder is closed on both ends. The cylinder is only 2 1/2 as long as the width of the coil.

What you have now is a can. The coils are coiled around the can and the coils stretch almost half way acorss the length of the can. Inside the can is a cylindrical magnet which has slightly smaller diameter as the can. The magnet is almost half as high as the can is. The magnet is connected to a wire which goes through a hole in the cylinder cap which is on the opposite side of the coils. The wire has a loop on the outside. On the coil-side cap, the cap has a hook on the outside.

Lets imagine we shrink
the can to a small size but keep all proportions. Then the magnet is very close to the coils. When the coils are activated then the magnet is attracted with high force to the direction of the coil. The distance that the mangnet moves is very short but it moves with high torque because they are so close. Now make 10 of these and hook them together and activate all coils. The series of magnets and coils move 10 times the distance of one of these, but the force is very strong.

Lets say the distance between the magnet and coil in one of these is 1mm. The force will be strong but movement only 1 mm. If you connect 10 of these then you get movement of 10 mm on the whole string. You do not need to brake/ slow down the movement inorder to go the other way. The magnet slow down by them selves when the reach end station. If you want 5 mm movement without the need to slow down the movement then you just activate 5 of them. To make the string effiecient, do not reverse the movement until the magnets have reached a stand still by themselves.

This has probably been though of before, but to me this is the best way of copying a muscle cell. Lets say you have 5 of these strings. 2 below the wing, 1 above the wing and then on fron and behind the wing. The strings in front and behind are 5 individual strings. this way you get a very strong downward actuator which is same as a bird having very strong pectorial muscles. This way you are optimising the energy. The circular motor and crank is using too much energy for upward stroke and too little energy for the downward stroke so the motor size is not optimised. The muscles of a bird that pull up the wing are alot smaller than the muscles that pull down the wings, in most cases I think.

Any thoughs?

Thanks Graham Stabler for guiding me to finding a way to control the actuator.
FlipperSail is offline Find More Posts by FlipperSail
Reply With Quote
Old Aug 03, 2004, 05:39 AM
Registered User
Seale, AL
Joined Oct 2003
644 Posts
,,,
wmueller10 is offline Find More Posts by wmueller10
Last edited by wmueller10; Nov 04, 2007 at 09:51 AM.
Reply With Quote
Old Aug 05, 2004, 02:43 AM
Registered User
Johannesburg , South Africa
Joined Jul 2004
151 Posts
This might interest you
http://www.rcgroups.com/links/index.php?id=4317
markmi is offline Find More Posts by markmi
Reply With Quote
Old Aug 05, 2004, 10:48 AM
Registered User
Joined Aug 2004
6 Posts
MarkMi and Wmueller10,

Thanks I have check out the links.

What about I use a hard drive? If you scroll down almost half way down on this long page http://www.dansdata.com/magnets.htm you see a harddrive taken apart. As I see it a the hard drive arm moves back and forth. Problem is that the magnet is big to give the coil full motion so its probably too heavy for flapping flight but might do for flapping a fish.

How does a hard drive flapp? How is it controlled? What I am wondering is if I could, from a computer and RC control the flapping speed and amplitude of a hard drive arm.

Does a hard drive arm always move all the way over the hard drive surface and back, or does i move in many varied amplitudes? Since I dont know how to build electric boards I would like to find something that already exists and it seems that a hard drive already has this flapping movement. Problem is how could I control the hard drive arm?

Anyone know this?

I have an old laptop that works but the screen is broken. I could use it.
FlipperSail is offline Find More Posts by FlipperSail
Reply With Quote
Old Aug 06, 2004, 07:31 AM
Registered User
Birmingham, UK
Joined Oct 2003
100 Posts
Instead of using lots of short-stroke actuators in a line, could the magnet be made to move round and round the same coil to save weight?
That might give another advantage, too: could we then let the thing rotate at high speed by using gears. That way, the heavy "actuator" (both magnet and conductor materials are dense) could operate at at high frequency - which is why motors have such a high power density.
That could be harnessed by Graham's crank. Wonder if it's ever been done?
To get a greater down force than up, could we let the crankpin slide in a swinging yoke connected to the wing?
John Mack is offline Find More Posts by John Mack
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Suggestion How do you make a "Sticky" post in Vendors Forum? marjamar Site Suggestions / Complaints 1 Jun 21, 2007 02:10 AM
How do you make decals with a computer? Andy W Scale Kit/Scratch Built 50 May 24, 2003 09:12 PM
How do you make your E-Tek packs with the new PCB? Parkflyer Batteries and Chargers 8 May 13, 2003 06:54 PM
how do you make Krylon glossy p471701 Electric Plane Talk 6 Oct 06, 2001 06:22 PM
How do you make channels in foam? Jim McPherson Foamies (Kits) 8 Sep 21, 2001 08:00 PM