Carbon Fibre Brushless Gimbal for NEX and smaller.

I now have an RCTimer OpenSource BGC board ("Martinez") and a couple of LD-Power Gimbal Motors which are large enough for an NEX or smaller.  I looked over a number of BGC frames for sale but they all seem to incorporate metal or glass fibre, both of which do not have the same strength and low weight of carbon fibre.  Based on the connection system I had used on the first CF gimbal I built from scratch (servo based), I have come up with this design with the size needed for a Sony NEX and the adjust-ability to balance for any camera of that size or smaller to maintain roll balance.  Also, the base plate the camera sits on is deep enough to move the camera back to balance the weight on the pitch axis due to the size of the NEX lenses.  

Once I have hand crafted this design I'll post some video.  From there, if there is enough interest I may get a batch of these laser cut and put them up for sale.  Roughly $30 of 2mm CF board for this and whatever the rate is for laser cutting.

This specific design is for the LD-Power GM4008-57 motors which are 45mm in diameter, 21mm in depth and 85g each.  Still need to work out how many poles these motors have to be able to set up the firmware correctly.  If anyone knows please let me know?  I was planning on using the smaller LD-Power 2208 gimbal motor which was 39g or so but the eBay seller had the wrong picture and weight in the listing. 

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Comment by Luiz Miranda on May 28, 2013 at 5:38am

good job, count me in for one.., I am also looking for one that is specific for the GoPro

Comment by Rob_Lefebvre on May 28, 2013 at 6:28am

IMO, the fact that most of these gimbals have gone to aluminum construction is a good thing.  Thin carbon fiber plate is not as stiff as aluminum in bending.

Comment by Rob_Lefebvre on May 28, 2013 at 8:09am

Monroe, I think that is exactly it.  It's all been about looks.

You know, I've tried using carbon fiber tubes for the booms on my Helis.  You know, because they look cool, lighter weight, and I like the fact that CF is either straight, or it's broken.  There's no way you can have it slightly bent and not notice, leading to trying to solve some weird handling problems.

But what I found is that the CF tubes are quite a bit less stiff than the standard aluminum ones.  And the weight savings is extremely minimal.  At first I thought that it was because I was using Chinese made CF tubes.  So I sprung for a genuine Align tube.  It's nice and stiff.  But then I looked, and realized it is actually an aluminum tube, with a very thin veneer of CF on the outside!

I guess, in high performance applications like that, you can't hide the truth.

I also noticed this when designing my Octocopter.  Thickness for thickness, the aluminum plate is stiffer.

Comment by Rob_Lefebvre on May 28, 2013 at 9:24am

Yep.  Here's my new ugly but effective H-8 frame:

Welded aluminum.  It's a bit heavy, just under 1 kg, but I'm pretty sure I could stand on it.  So in fact, the strength/weight is pretty good.  And this is for an industrial type application, so it suits.

Comment by Josh Potter on May 28, 2013 at 9:57am

But then I looked, and realized it is actually an aluminum tube, with a very thin veneer of CF on the outside!

Yeah I got a kick when I noticed my last trex kit shipped with two different tubes, one looked like plain aluminum and the other looked like carbon fiber.  Then I also realized the same thing as Robert, they were both aluminum and one of them just looked "cool".

Comment by Rob_Lefebvre on May 28, 2013 at 10:18am

Yeah, I felt a big ripped off.  I mean... why not tell us exactly what we're getting?  I wouldn't have paid extra.

On my 450, I tried a real CF boom tube, and it was a disaster.  Horrible, horrible vibrations.  I mean, the tail lit up like a paint shaker.  The heli was shaking itself apart.  I fiddled with it for a bit, not realizing the boom was the problem.  Then I stuck the aluminum tube back on, and boom, perfect.

Not saying carbon fiber is no good.  It's great in the right application.  But 1/16" CF plate is not strong in bending.  I think the problem is that the fibers are only strong in tension.  They are not strong in bending.  And a thin, woven CF plate, basically have the strands in an accordion pattern, if you cross section the plate.  None of the strands are in pure tension when you try to bend the plate. They are all being bent again, like an accordion. Or, consider the stiffness of a Slinky, compared to a solid steel tube of the same dimensions.  That's what you're getting.

I don't have a good answer for why the CF tubes are also flexible.  But I suspect it's because they also have not enough CF by volume.  Too much epoxy, and then a clear coat so they're pretty.  

Comment by Gary McCray on May 28, 2013 at 10:27am

Hi Robert,

Nice welded frame, the 4in 1 ESCs seem like a good idea too, although I's guess that isn't where you'll be mounting them.

That looks like 1" or larger square tube and the inner motors have 3 places where it interferes with the thrust, probably unavoidable.

It will be interesting to see how lift varies on your 4 inner motors versus your outer motors.

I'd actually really like to know that.

Nice welds on that thin tubing.

Comment by Cloud9Drones on May 28, 2013 at 11:23am

Count me in as well

Comment by John Grouse on May 28, 2013 at 2:02pm
Wow, how did my blog post diverge into CF on 450 heli's? Back to my design, I have found that the 2mm CF boards at the dimensions of this design to be very solid and most importantly light, regardless of what it looks like. If I'm going to slap a Sony NEX on a 1kg frame, trimming extra weight off is going to be high on my list.
Takes a good amount of force to bend them. I may end up with AL for the connection between the gimbal and the multirotor if the rectangular CF tube introduces vibrations, but I think it should be fine. Hopefully the CF board will arrive soon so I can get cracking on it.
Comment by John Grouse on May 28, 2013 at 2:09pm
I'll do the smaller GoPro design once I perfect this one. Should be a matter of scaling it down.
Requests for quotes to cut CF are out so I should get an idea what I could sell these for.


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