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Old Jun 11, 2012, 01:51 AM
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Ornithopter Engine using a servo

I am thinking of building a flapping wing mechanism for a bird using a standard servo and a belt kind of mechanism. Idea is to increase the gear ratio. I have tried using a servo directly as a flap mechanism and the flap rate is too low. Now I am thinking if we use some mechanism to increase the speed by way of a gear mechanism (generally we use reduction gears in these), what kind of a success rate I will have?
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Old Jun 12, 2012, 09:58 PM
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I am thinking of building a flapping wing mechanism for a bird using a standard servo and a belt kind of mechanism. Idea is to increase the gear ratio. I have tried using a servo directly as a flap mechanism and the flap rate is too low. Now I am thinking if we use some mechanism to increase the speed by way of a gear mechanism (generally we use reduction gears in these), what kind of a success rate I will have?
Mrexel I like the first part of your idea ((using a servo) and does';t like second part
(using increasing RPMs stage after the output servo's shaft) because wasting of the efficiency and increasing the weight and complexity.
You can easily achieve higher RPMs on the output just by skipping one or two first reduction stages in servo reduction box.In this case you will need stronger motor and you can use the small pinion part of the last skipped stage compound gear for the motor pinion . Usually in metal gear servos compound gears are made from two parts pinion and spur gear and they are assembled by press fitting .So some more pressure in opposite direction and you will have the pinion that you need. Don't forget to rework your servo for continuous rotation along that.
When choosing the donor servo check is any machined aluminum servo arms available for that servo. This will almost resolve the crank design and manufacturing problems . Also be sure that servo output shaft is double ball bearings mounted.
IMO metal gears servo with more than 10kg/cm max. torque will work well for ornithopters with up to 1m wing span and up to 250 g weight .The maximal output shaft rotation speed that we are looking for is about 360 - 400 RPM.
Another simpler way is just to replace the servo motor with some with higher RPMs IMO in every one of the described by me cases, you will need new suitable motor's speed controller. The best choice is some brushless outrunner with appropriate ESC
Success
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Old Jun 12, 2012, 11:03 PM
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Thank you for the detail insight!
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Old Jan 15, 2013, 11:53 PM
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Because I like the idea,I just want to report my finding:http://www.hobbyking.com/hobbyking/s..._0_03_61g.html

This ultra fast servo is able to turn its arm on 60 degree angle only for 0.03 s.
This mean that if it be reworked to turns continuously it will turn its output shaft with 333 RPM or 5.55..Hz - without load! Most probably it will be able to power an ornithopter without need of heavy mechanical rework.
Its max torque is 8.4kg/cm. and it is high voltage servo, so you can power it directly from 7.4 V Li-pol battery.
Its gears are made from titanium alloy - strong yet light
Output shaft and last stage gear is supported by two ball bearings.
The output shaft splines are Futaba style 25 T and there is aluminum servo arms available which can be used like crank arm.
http://www.hobbyking.com/hobbyking/s...M2_Futaba.html
For position feedback it use not standard potentiometer but magnetic rotary encoder which probably isn't restricted to turn only on 270 degree and if it allow more than 360 degree rotation it can be used for position sensor for the GLDAB controller (after appropriate reworking its hardware and software)

The weight is 61 gr. and the price is 36$ but for this price and weight you receive gearbox,motor,speed controller and I hope installed output shaft position sensor .

Most appropriate scheme of converting rotary to reciprocating motion using servo is every one with crank shaft pointed along the ornithopter frame .

There are few examples of such type a mechanisms:



da vinci history the worlds smallest ornithopter (5 min 14 sec)


ornithopter Magic Bird 불사조V2-기어 (1 min 10 sec)


Ornithopter Drive (3 min 24 sec)
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Old Jan 16, 2013, 12:28 AM
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Thank you very much
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Old May 06, 2013, 09:04 AM
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power to weight ratio

The key to using servos to drive the wings is power to weight ratio. In my research, I found that the Futaba S9352HV is the highest power to weight ratio servo you can buy. For that calculation I just multiplied the servo speed (deg/sec, not sec/60deg) by the peak torque quoted by the manufacturer.

The second key is you must operate the servos at 50% of their top speed to get full power. So, the wings or any mechanism you design should be putting you at this flapping speed.
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Old May 07, 2013, 10:45 PM
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The key to using servos to drive the wings is power to weight ratio. In my research, I found that the Futaba S9352HV is the highest power to weight ratio servo you can buy. For that calculation I just multiplied the servo speed (deg/sec, not sec/60deg) by the peak torque quoted by the manufacturer.

The second key is you must operate the servos at 50% of their top speed to get full power. So, the wings or any mechanism you design should be putting you at this flapping speed.
I think, the main key has to be : reworking the servo for continues rotation! That's why I redirected you here.
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Old May 07, 2013, 11:08 PM
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thank you
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Old May 08, 2013, 01:31 AM
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Originally Posted by gerdes1723 View Post
The key to using servos to drive the wings is power to weight ratio. In my research, I found that the Futaba S9352HV is the highest power to weight ratio servo you can buy. For that calculation I just multiplied the servo speed (deg/sec, not sec/60deg) by the peak torque quoted by the manufacturer.

The second key is you must operate the servos at 50% of their top speed to get full power. So, the wings or any mechanism you design should be putting you at this flapping speed.
Have you noticed any wear or overheating problems using the servos in this way? Any gear train failures?

Steve
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Old May 13, 2013, 12:06 PM
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Just another way of thinking...

What if I use a pre-recorded ppm signal feed in to the Tx trainer port, which will continuously move the servo arms in an alternate action and then use that to flap the wings ?
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Old May 14, 2013, 02:09 AM
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Just another way of thinking...

What if I use a pre-recorded ppm signal feed in to the Tx trainer port, which will continuously move the servo arms in an alternate action and then use that to flap the wings ?
How you plan to control the flapping frequency?
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