Brainstorming Ideas for 90 degree movement for arms on a drone

[bddp9]

Hello,
I've been working on a drone project and need some help with a mechanism for closing and expanding the drone's arms. Please see image below. What are some alternatives? Right now in my model i have a small servo motor and gears that can open the arms. Any alternatives? The OD is 45mm. The top half will be for batteries and the bottom will be for anything electrical or mechanical.

 

[3DDave]

Typically a servo is used when control at every point in the range is required. This only needs two end points, similar to a windshield wiper typically has (not the fancy ones with the separate park position) and so a motor with a crank or a linear actuator could work.

How much force is expected for the device to overcome and how fast does the change in position have to be?

For example, the deployment could use a pre-loaded spring for fast extension and then a little geared motor to pull it back to stow it. This is how insects handle jumping motions and why, for example, a dead cricket's hind legs tend to extend (depending on the manner of death.)They preload the extension tendons and then have an over-center mechanism that uses a tiny muscle to release it.

If there is a microprocessor involved, and they really are cheap enough for it, they can monitor the current drawn to see if a dumb motor (not a servo) has reached the end of travel because the current will shoot up. This saves having switches or encoders or other continuously measured position sensors.

If very clever the motors that drive the propellers could have a one-way clutch so that, if run slowly backwards, the flight motors themselves could be used to operate the extension/retraction system.

I do wonder about the case for autonomous deployment.

 

[rb1957]

how simple can you go ?

why are you moving the arms ? deploying the rotors (pre- and post- flight) ? a simple link would lock them in place, adjusted manually.

if deploying in-flight for some stability concern, then you need the high tech solutions ...

"Wir hoffen, dass dieses Mal alles gut gehen wird!"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[bddp9]

I don't know the force required yet. I would like to keep it as light as possible with brushless motors and propellers. RB1957, As soon as the drone is in place on the ground I'd like to press a button and the arms expand out then when it is time to retrieve they will close. can open and close the arms at the touch of a button. I like the idea of using some springs and then having a motor to close the arms. Maybe a linear worm gear running in between the gears. One at the front and the other in the rear.

 

[LittleInch]

How are you going to fold the rotor blades in?

More motors?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[drawoh]

bddp9,

Why can't you just design the arm to snap into open and closed positions? Is manual actuation too much trouble? You get rid of the servo motors. I don't think brushless is any lighter than regular DC[ ]motors. You will need to design plastic snap catches.

--
JHG

 

[bddp9]

The blades I haven't thought about could be worth looking into once I figure out the 90-degree open/close mechanism for the arms. I dont think that will need additional motors. Maybe i can get by on my first test run.

 

[rb1957]

Sure "pressing a button" is a solution and having some mechanism accomplish a simple operation (countless cartoons come to mind).
Sure doing it manually maybe be too "uncouth" (or "agricultural" as I express that type of thing at work).

If you (or w) are clever enough, you should be able to do this with a single actuator.

"Wir hoffen, dass dieses Mal alles gut gehen wird!"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[zeusfaber]

Why do you need the arms to retract? Is it for compatibility with some sort of launch/retrieval system? Could you build the fold/unfold actuators into the ground system instead (so you don't need to fly their weight around)?

Or just cgi the fold/unfold in afterwards?

A

 

[Scuka]

Steal some ideas from gripper mechanisms. A lot of times they're doing this exact kind of motion.

 

[LittleInch]

Have you thought about folding them upwards instead?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MintJulep]

It doesn't seem like the arms could move 90 degrees in either direction from where they're drawn now.

 

[Orange_kun]

If there's a human nearby when this thing is launched or recovered, I have no idea why you'd eschew manual deployment. Talk about over-complicating it.

Spring loaded locking mechanism and two detent locations. It'll take all of 20s to deploy. Save the weight that would be frittered away on servos etc and give yourself better flight duration and reliability. You've seen the things DJI does, right?

 

[ctopher]

Looks like a school project.
From the side view, not sure why the blades are below the body.
I agree with the other about the manual part.

Chris, CSWP
SolidWorks
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