Cnc Milling Quadcopters arms

[Drazen Bencevic]

Hi guys.
I am from Croatia, and this is my first post. I am a mechanical and structural engineer.
Recently, I designed some arms for quadcopters. ( For my friend )
After several weeks of prototyping, on the 5 axis cnc machine, I finally managed to get a fantastic mechanical and static results.
The structure is designed to absorb all kinds of vibration.
Bending arms at a load of:
1 Kg - 1.7%
1.5 Kg - 2.6%
3.0 kg - 5.4%
5.0 kg - 8%
After each bend arms go back to their original positions.
10:00 Kg 14.5% ( Arm was not completely returned to its original position )

specifications:
Material: Alluminium 7075
Dimensions: 20 x 20 x 315 mm
Weight: 30 grams.

I also invented some different ways of mounting the motor on the arms.
So, let me ask you for your opinion??
What do you think?
Would you purchase this arms for 20 euro??

 

[Mike]

20 euro per arm or for four? How much would you be charging for international shipping? Also, would you only be making them in the 315 mm length? That would be for like a 650 quad, right? Are you making anything shorter?

 

[Drazen Bencevic]

$20 euro per arm or for four? How much would you be charging for international shipping? Also, would you only be making them in the 315 mm length? That would be for like a 650 quad, right? Are you making anything shorter?

The price is 20 Euro per arm. Shipping price is not known at this time, but I'll try not to be too expensive.
It is possible to create different lengths, for which length you interested? Can you tell me, what's your opinion on this arm?

 

[Mike]

20 euro is a fair price if the arms perform well - but I don't know how many people would buy just arms at 20 euro each unless they were replacements. For instance, the arms on the QAV500 are USD $22.99 each for replacements. when you have a $200 frame and you break an arm, most people will gladly pay that much for a replacement arm rather than replacing the whole frame. When it comes to building a custom frame, I would personally buy cheaper arms since I could get rid of a lot of vibration with bobbins and other methods.

With that said, if you design/build/sell an entire frame that utilizes those arms, I think you could sell that for quite a bit - and each arm would probably earn you more than 20 euro.

That's just my opinion though. Maybe some others would buy them for 20 euro each + shipping.

I'd be interested in 215mm length arms if I was buying - but how do they attach to the frame? Are there pre-threaded bolt holes or anything on the arms on the frame side?

 

[Drazen Bencevic]

Thank you for your response. Really useful advice. How did you think that you can solve the vibration, which method do you think.
For the arm attachments to the frame there are holes for screws.

 

[Mike]

A lot of frames dampen vibration by separating the plates that connect to the arms from the plates where cameras will be mounted with vibration dampening "bobbins":

http://www.fpvmanuals.com/wp-content/uploads/2013/02/qav400-15.jpg

That's a QAV frame. Another plate goes on top of those orange bobbins and you'd mount the camera there. This eliminates just about all vibration if you have a good setup.

Or they'll put them where the camera gimbal or mount attaches to the frame:

http://i00.i.aliimg.com/wsphoto/v0/...ion-Plate-GoPro-Mount-Adapter-Black-Light.jpg

You can also buy all sorts of anti-vibration blocks or vibration damping balls:

http://www.hobbyking.com/hobbyking/store/RC_PRODUCT_SEARCH.asp?strSearch=vibration+damping

http://www.hobbyking.com/hobbyking/...Rubber_Mounting_Blocks_M6D17_5H16mm_5pc_.html

http://www.hobbyking.com/hobbyking/store/__13214__Aniti_Vibration_Rubber_5pcs_bag_.html

I still think your arms are very nice and the vibration reduction is still very useful (you can never have too much). The design is cool too. Plus if your motor mounts are very unique, you might have something there. If I were you, I'd design an entire frame and sell the frame kit as a whole.

 

[Drazen Bencevic]

Thanks for the compliments , just working on the design of the entire frame , I think it will be something special . At this point the weight of the entire frame is less than 200 grams . Dimensions are 550 x 550 mm . As for the engine mount to arms , it's something unique for now . The whole setup of arms is mounted in less than two minutes . The total weight of arms and motor mounts , is a total of 32 grams , one arm . At the same time I started the branding of the product and the entire frame . When it's done , if you're interested in testing and review , I will gladly send you a kit , since you showed a good man , for you, is totally free .Maybe if you're interested for distribution and sale in the country where you live? ? By the way, my country and the area where I live at the moment faces a flood of biblical proportions , where many towns and villages were completely flooded and where tens of thousands of people left homeless .That's why I'm currently short on answers and because now all go a little slower. Basically, I am well and beyond any danger . Check Croatia flooding ...http://www.bbc.com/news/world-europe-27459184

 

[Drazen Bencevic]

P. S. I looked at the attached links, my approach is that it is important that the entire structure of arms and frames must be as light as possible. Course and must be strong enough. It is better that arm vibration-free, because supplements only increase the weight.

 

[Mike]

No worries about the short answers. I'm sorry about the flooding - that looks terrible.

Oh, wow - I didn't realize you were going to be able to get the weight of the entire frame that low! In that case, yeah - the weight of antivibration balls really would make a difference. With your design, is there still a good amount of room to mount components on the frame? 200 grams is amazing. I think if you can pull it off and it really does eliminate a lot of vibration, it would be pretty special. Even the most basic 550 frame like an X550 from HobbyKing weighs 315 grams (frame only). A QAV500 is 500 grams - which is pretty good considering all of the materials used. The Turnigy Talon is extremely simple and made from carbon fiber and it even weighs 280g (frame only)

I'd definitely be interested in a frame to review once you get some produced. I'd be willing to pay though.

As far as distribution goes, I'm in the US and I actually run quadcopterframe.com. I launched it recently with just some basic frames to get started, but I'm getting ready to start adding variety to give my customers more options. So I'd definitely be interested in talking about distribution.

 

[Drazen Bencevic]

You said you were interested in the arms 215 mm long. Is it the total length of the arm or part of arms coming out of the frame. Can you make a sketch and send it to me in the mail ... I want to create a model of the arm for 215 mm, to compare the weight ...
at the same time, if we can continue to correspond via e-mail

 

[Mike]

I was thinking that 215 would be nice to replace arms on a 450 frame, but since you're making an entire frame and it's going to be so light anyway, I'm thinking 550 is the way to go. If you do want to look at the weight difference, most popular 450 frames have 215mm arms. I will PM you my email address.