Whoa that was a sick video man from the flying to the music to the color correction. Whatever that process is you did, that video is legit!!

Guys, if you can please post pics of the broken arms. I just want to see how I can make them stronger somehow.

Plus one on the video, nice colour grading there. 


Here's two pics of the broken arm. 

Thanks so much jasper, that is so helpful. And this a crash into a tree?

Mine is same to jasper's.  Right on the mount point it bent.




Without changing the design of the mount point of the arm to chassis I would just make the arms thicker.  thicker to the point that still keeps it sub250.

My questions to Jasper and Ph2t:

1) Did the damage happen with an easy crash or a hard crash??
3) Did you use the bottom brace that is supplied with the frame or did you leave this piece off ???
    {I can't really tell from the pictures}

If the bottom brace was not used, then perhaps using the brace might prevent this type of damage.
If the bottom brace WAS used, then perhaps a solution might be to modify the bottom brace and extend it out  under the arms a bit so as to provide more support where the assembly hole is located. 

Although I did NOT use the brace, I think now that I will. 

Just me, but I think that I would work on brace modifications first, before adding more weight to the arms. Just my thoughts 

good points ifly, extend the mount past the bolt hole instead of thicker arms..

1) Dropped out of the sky, approx 50 meters, onto grass.
2) Yes, used the bottom brace (1st page of this thread )

how hard a crash is is pretty subjektiv, it can look gently but is hard. only longterm use show the true durability. 50m sounds like alot force to that arm.

i beleive the bottom brace isnt the important thing.
the question is just where the breakpoint will be xD and where the breakpoint would be which providing the best rigidity over all. my experience is the best rigidity is if the breakpoint is between 1/4 and 1/3 of the arm.


the best rigidity breakpoint would be where the yellow arrow is.
it can be improved to that direction by add some carbon around the hole, get the same overall arm wideness diameter where the hole is.
anyway it might not be a new world in rigidity, probably a tiny bit and a changed breakpoint.

I broke it at decent speed against a gum tree doing proximity flying. I had hit harder at other times and it may just be the angle of impact and cumulative stress. And I do use the bottom reinforcement plate.

Thanks guys this is really good feedback. The bottom brace was meant more for addressing motor vibes from larger motors from when prototype 1 couldn't even handle 200X motors. While I still recommend 15XX max, at least I know it can now handle 200X leaving a lot of headroom The brace was not really meant to prevent arm breakage - if anything, I suspected it would focus impact on that very area where we are seeing the break or bend.

jasper, I know you fly like a sbang sbang madman so - and please don't take this the wrong way - I'm not as concerned with your breakage. At least it makes some sort of sense.

But ph ... a 150 foot drop ... onto *grass*?? That threw me for a loop for a bit. But then I realized you are carrying basically a GoPro and a 6S lipo. That's a lot of momentum for this frame design even on grass.

Still, I think hugs nailed it and the fact the area of breakage is pretty much in the same spot confirms that is a weak area. I had considered thickening the arms but that is actually standard thickness for other 4 inch frames. What I may do is widen the arms. I think I followed too much of a toothpick style hoping to shave as much weight as possible. Now that I see there's some room on the weight, I will focus that on reinforcing the arms.

However, I don't plan to do a Ronin Mk1.75 but rather taking all of this into consideration for the entire line of Mk2 chassis. With that said, ph has already requested thicker arms which I plan to put in as a one-off special order when I do the Sohei production run soon. If others think thicker arms are worth it, I can put in a run for a batch and sell that as upgrade arms.

Hi Ronin,

If you order some extra "just arms" that are wider, put me down for a couple of sets.