Twitchity quad with power board - test build

[jhitesma]

Don't get me wrong, Kapton is a great insulating tape that's very strong. I'm just wary of using it specifically to prevent abrasion given the FAA's findings about it's poor performance in that one regard. For things like insulating terminals on a lipo it's a great solution. I just don't think it's a good call for the purpose of providing mechanical abrasion protection.

 

[jhitesma]

So I haven't updated this lately. I've been flying the snot out of this little guy despite the damage from the meltdown. Twitchity sent me some replacements arms but for reasons I can't really go into just yet I'm still flying on the original damaged arm. The silicone tape I used to insulate the arms has been working well. It was a major pain to get installed cleanly, and I had to snug the frame bolts a couple of times as it compressed down - but so far so good.

I've even tossed some gemfan 5" props I had laying around on it and have let a few friends with minimal or no experience take it for a few flights. Unfortunately right after new years an arsonist torched or city's amazing "castle park" next to the field I fly at - but making lemons out of that lemonade it means I've been able to fly over the field a lot more since no one is up there. (And the city plans on rebuilding - but they're still investigating the arson, talking to their insurance company and deciding the best way to move forward with rebuilding which likely won't happen until next year.) So we lost one of our prize community assets for a year or so...but I get to fly at the field over grass a lot more since there's no one there now.

Everyone who's tried the Twitchity acro loves it. My friend with a warp had a blast with it, and even the complete noobs had fun once I loaded a profile with tamed down rates and put it in horizon for them. Of course that also means it's taken some really hard hits lately. Just yesterday it had it's hardest hit yet. My co-worker I gave the G10 frame to got to try it but lost orientation and then panicked throttling up instead of down. I eventually convinced him I was serious when I told him before we started that if he got into trouble to just disarm and let it fall which he finally did from about 200m away and oh...70-80 feet up....over pavement.



Ouch. That wasn't just due to him...mostly it was due to an issue I can't really go into just yet combined with a few weeks of hard crashes. He felt horrible but I reassured him I had two replacement arms at home and more on the way. Besides, the fall didn't even break a prop (it did bend one) since we were on the cheap flexible gemfans - so I immediately put it back in the air to show him he didn't really do any serious damage Worst part of it was I got a CF splinter from the damage

But...today I got a care package from Twitchity:



(Don't mind that balsa in the background...I kind of started another project I've been meaning to get to for some time...I've been a bit too focused on multi-rotor flight lately and felt a need to take on a project I've been wanting to tackle for about 30 years.)

I've been looking forward to this for a few weeks The new v3 PDB is exciting to have along with a replacement bolt/nut for one I stripped.

Enlarged gaps between the copper and the holes so the heads/nuts won't short out to the ground plane anymore:


And positive copper removed from under the arms - so both sides of the circuit are now protected from shorting out.


As exciting as the new improved PDB is what I'm really excited about is the new arms he cut for me. This is 100% experimental and something I've been wanting to try since I heard about picnic quads and the hybrid carbon birch material from DragonPlate they use in their micro frames. Twitch and I have talked a few times about trying this but neither of us were ready to put the money into trying it. I finally decided to put my money where my mouth is and return the favors people have been doing me by financing a sheet to experiment with. So save money I opted for a discontinued size sheet in the matte finish which is a bit cheaper than the gloss and supposedly more scratch resistant.

Here's dragonplates page about this material: http://dragonplate.com/ecart/categories.asp?cID=3

They claim that it's both stiffer and lighter than solid carbon. Sounds perfect...but let's see how it works in practice! We went with the 5/32" thickness which is about the same as the 4mm all carbon used so far (My calipers put it about .01mm thinner).

Twitch and I are still debating the best way to make some actual strength measurements on this stuff...but initial impression is that it's not actually stiffer as claimed as it seems to flex a bit easier than the pure CF. However it is considerably lighter.

The two biggest issues I have with it are:

1) The bottom is a textured rough finish - not very attractive. The exposed birch around the ends may be unattractive to some people as well. So it's not the prettiest material - but I'll take performance over looks any day.

2) The CF laminations are very thin and I worry about how well the exposed birch on the ends will hold up in crashes. I'm thinking about mixing up some slow curing epoxy and letting it seep into the wood on the ends to help seal it.

Here's some comparisons showing the difference in finish and weight.

DP Hybrid arms on the left - matte side up. Spare DPH arm "textured" side up in the middle. Original matte pure CF arms on the right.


DP Matte finish:


DP "Textured" finish:


Original non DP matte CF:


DP Matte side up at top, DP textured side up in the middle, original matte on the bottom:


I only have 2 unused arms from the original CF so I'm only comparing 2 arms instead of a full set of four...but the original arms came in at 18g for two (so we'll assume, 36g for all 4)


The hybrid CF/Birch arms however came in at just 10g. (so we'll assume 20g for all four) So overall switching from four CF arms to 4 hybrid arms should save 16g overall - nearly half the weight. Not a huge difference but every bit of weight shed is a bit more flight time, a bit more performance and a bit less damage in a crash....


One last look at the DP finishes:



So I'm excited to try these. I'm going to epoxy the ends to protect them a bit and I'll have to sand the sharp edges (the edges are sharper than on the pure CF Twitchity has been using.) so it will be a few days until these are ready to go on the quad. But I can't wait to try them! They do seem a bit less stiff which may or may not be a bad thing...maybe the birch will help absorb vibration from the motors, maybe the loss of stiffness will make vibrations worse. Maybe the wood will get damaged in crashes, maybe the ability to flex will help it hold up better.

Stay tuned. Twitch and I are talking about various tests we can put this material through to see how well it holds up and whether it's a good option or not. It is more expensive than the CF he's been using so the benefits would have to be pretty good to justify switching to it. But it might be something he'll offer if it works out well. Or I may have just tossed away some money on some material that is weaker and more expensive. Either way this is how we learn and I'm always up for learning something new

 

[cranialrectosis]

Something tells me you will manage to toughness test it pretty well whether or not you really want to...


If you hate the color of the underside of that, you can always paint it. Barbie pink seems to be popular with your biggest fan.

 

[jhitesma]

Well, I struck out on 30 minute or 1 hour epoxy at 3 different stores. 5 minute epoxy just won't cut it for this since I need it to soak in. So I'll have to hit the LHS tomorrow (they were closed for inventory today). But I couldn't wait...had to get this back together:

No props, we came in at 173g. Nice.


With props ready to fly except for battery - 190g. Before it was at 208g so I shed 18g with these arms. About a 8% weight reduction...not to bad!


With pack I'm at 296g ready to fly.


My temporary silicone insulation worked...but didn't work great. It got pretty tore up from me putting the screws through. This was the worst one. Not sure how much of that was from installing the screws vs. removing them.


Thankfully I don't need the extra insulation anymore. The PDB has been redesigned so that's not an issue...and even if it was with the birch in the middle these arms are only conductive on a side not across the entire arm. Of course the bolts are still conductive but they shouldn't make contact without the arms being conductive. But with the fixed PDB there shouldn't be any chance of shorting out now.

Can't wait to test fly it but I've got a pretty full schedule tomorrow so not sure if I'll get to do it then or not. And I'd kind of like to soak the ends/edges of the arms in epoxy first...then again might be fun to get in a few crashes without doing that to see how these arms hold up....

 

[JBarousse]

This definitely looks like something I'd be interested in...

 

[Twitchity]

jhitesma, how do you think a thin/medium CA glue would work instead of the epoxy? I know it would seep into the wood nicely but I'm not sure about how much strength it would add. I must say that hybrid stuff is ugly (especially the textured side), but it does save a good amount of weight! When I was weighing the arms I was seeing about a 40% reduction in weight as well.

Now that you have the quad back together I know it will only be a matter of time for a durability report to pop up on the forums for this hybrid material. And I think Cranial has a great idea. Pink does seem to be a favorite around your house, so you should paint the edges of those arms pink to keep everyone happy.

 

[jhitesma]

I thought about CA...but the problem is CA tends to be brittle itself. So I don't think it would give the same kind of strength as a nice slow epoxy. The slower the epoxy the more it can soak in and the more it will probably help...but...the more that soaks in the more weight it will add.

So I think I'm going to toss caution to the wind and fly a few packs with no glue just to see how they hold up.

The textured side is ugly. The photos don't do justice to just how ugly it is. The matte side isn't the prettiest either, not as nice as the matte on your other material - it still has a it of shine to it and it's not very smooth. The glossy is only a few bucks more and probably looks a lot better...but even that has the ugly side.

Still. Up in the air the ugly side won't matter, and in fact being that textured vs. glossy may possibly have a slight chance of helping in some situations with orientation (to squeeze in as many non-committal terms as I can!)

I don't thin paint would help much either, it's the texture more than the color that's an issue. A coat of finishing epoxy would help...but again...that just adds more weight. I'm thinking this material is getting into the "racecar" class - toss looks out the window and let durability take a backseat to performance while draining your wallet. I don't think it will be a very popular option for most people...but for those who want the ultimate in performance...I think it has great potential.

Pretty windy out today...just got back from a 5k "Volksmarch" put on by our favorite local german restaurant (any 5k that ends with a free 1/2 liter stein and a bratwurst is worth $5 in my book...even if the brat and the beer in the stein cost extra!) going to to hit the LHS for a few things and then if I have time I'm hoping to do a test flight. But I've got a friend coming over who wants me to look into fixing an antique commercial espresso machine for him so I may not get to test fly until tomorrow. We'll see. I'll stick to acro only to assure the highest chance of durability testing

 

[x0054]

From the looks of it it's mostly birch plywood with a thin single layer of epoxy on both sides. You know how you were going to do some stress tests, I think it would be interesting to do some stress tests with just normal birch plywood, because something tells me that it could be almost, if not exactly, as strong.

I don't know why they leave that inner edge so ugly though. I purchased some CF for twitchy to cut Foldy 2 for me. The first batch we purchased was this red CF, which looked really nice on one side, but the other side was also very rough and ugly looking. I was told by the company that it has to do with the kind of CF press they use to manufacture the sheets. We returned that CF and I ended up ordering some sheets from China, just couldn't find anything here in US.

- Bogdan

 

[jhitesma]

Yeah, I expected the CF laminates to be a bit thicker.

However I'm back with my first durability report and it's not as good as I had hoped for:




Video will upload shortly. This was a couple of good but not overly hard crashes into a "grassy" field. First few went as I expected...bit of damage to the props but the frame held tough. But that luck didn't hold out

So yeah, I'm definitely classifying this as "race car" material. It's definitely stiffer and stronger than plain birch. I have some similar thickness birch here and I can bend it much easier than I can bend this even though the birch is almost twice as wide. But it's also definitely not stiffer than pure CF and considerably weaker.

So for ultimate high performance I'd give it good marks, it's light and stiff and felt great in the air. But like most high performance things it has it's drawback - ugly backside, less tough and more expensive.

Laminates do make a lot of sense. You gain a lot of strength without a lot of weight by hybridizing materials like that. But it's not strong enough to "fly it like you stole it" like you can an all CF or even G10 acro quad.

As for toughness, I actually think the laminations may be working against it somewhat by preventing the wood from flexing and absorbing some of the hit. I had hoped that the CF would be strong enough to compensate for that but it seems it just makes the whole thing easier to snap. For a micro brushed frame...I'd go with it no problem. But for something with a multi cell battery pack and the associated weight...I think I'll probably stick with pure CF

I'll probably still fly the hex with arms from this just to try it though

 

[Twitchity]

Wow, that didn't even last one day. I believe someone told me they wouldn't be needing replacement arms I still have some more of the hybrid material so I can get you around 2 sets of spares if you'd like, or I can save it for another project you might have in mind.

From the picture it also looks like it broke in the middle of the arm, and not where the motor bolts on or at the the frame. Well on the bright side, it looks like I won't need to do any strength tests on that material.

 

[jhitesma]

One day...not even one pack...heck not even half a pack Yeah, it broke right in the middle. I think I'll take my replacements out of normal CF when you get more in I have some ideas for this stuff but not as arms. I really didn't expect it to snap in the middle like that after just 4 crashes...it wasn't even that hard of a crash:

If I was using it for competitive racing...I'd be ok with these arms and would just consider replacing them part of the cost of racing. But I'm flying for fun so it doesn't make a lot of sense for me. I still have the spare you sent so I can toss that back on. But for my kind of flying ruggedness is more important than ultimate light weight. If Mustang wants to try them for his racing though he can call dibs on some of it. If not I'll try and think up something else to use it for.

Arms from it may may work better if they were a little wider...but then you'd gain back some of the weight and I'm not convinced the birch core gave much in the way of vibration isolation or any other benefit. My 1/2" wood boomed 250 class mini held up just as well if not better and weighed about the same but cost a LOT less. So if I wanted the benefits of wood I'd stick with that.

Oh well, figured it was worth a try. Still wouldn't mind cutting a micro brushed unibody frame out of this material or using it as parts in a plane or something. But for brushed multi arms I think it would have to have a higher CF to Birch ratio to work well.

 

[Balu]

Is it birch plywood sandwiched between two CF layers?

I wonder how that would look if they'd mix a CF layer into the plywood instead of just putting it inbetween. The aircraft beech plywood I'm using has 5 layers...

 

[cranialrectosis]

I think it might make nice ribs on a balsa build or maybe knuckles for an H or I quad.

Sorry man. But thank you for the lesson and for posting it here win or lose.

 

[jhitesma]

@balu - yes it's birch between two thin CF layers. It appears to be 1/8" birch. The CF definitely adds a lot of stiffness and strength...just not enough I think thicker CF and thinner ply would work better than adding CF into the ply. I suspect they buy the ply and laminate it so since they aren't making their own ply they can't put CF internal anyway.

I know when I laminated 1/8" ply with plastic gift cards it got stiff enough I couldn't bend it. The only time it failed was when the bond between the epoxy I used and the plastic let go. That was a big part of why I had high hopes for this. I just think the CF is too thin of a layer for our needs. If I had the money I'd try one thickness up - it may give more strength with minimal extra weight. But I don't have the funds to keep experimenting If someone could find a manufacturer who would make something similar with twice the thickness of CF as this I bet it would be perfect.

@cranial - Would probably make great knuckles...maybe I'll ask Twitch to cut some for me with the rest of it Though my lexan knuckles are working great so far so I'm not in a rush to replace them

Might be heavy for ribs on anything small enough to fit on my build table But for bulkheads in high stress parts of a fuselage I could be great.

I knew it was a risk trying it...but after seeing how laminating plastic cards on ply worked I just had to try this stuff. It's really amazing material...just not quite up to snuff for arms like these.

It may do better on the hex where the arms are thicker. I'm really itching to get the hex together now. Might make progress on that tomorrow as the quad is now grounded for a bit anyway while I wait on Twitch to make me new CF arms (and he's still waiting on more CF himself) so I don't mind stealing those KISS's now. Just have to finish gluing up this wing on my bench before I can dig in on the hex:


(Going to go do that after I catch up on the forum! Spent the day helping a friend refurbish an 1950's manual espresso machine then testing it out with some of my home roasted beans....so I'm not quite ready for bed just yet )

 

[nilsen]

Hey Jhitesma,

Sorry about your arm, I guess if you never try you'll never know...

Have you considered using Sugru as an arm "bumper" like a phone case?

It's really strong, I use it on my tripod legs and you can make it pretty thin.

Cheers

 

[jhitesma]

I've thought about it...but I don't think a bumper would have helped here. It would help on the G10 since the big problem there was the ends getting torn up. This was from the center flexing in a crash and a bumper wouldn't really help. I thought maybe the flexibility of the birch would help absorb crashes like the G10 does...but the CF laminates would give the birch the strength it needs to keep from snapping like this. It lasted for three crashes at least

 

[Twitchity]

Another experiment may be getting two think birch/CF laminated sheets and then laminating them together yourself. This probably wouldn't save you much weight over pure CF though, but it would be interesting to see how stiff it made the piece.

 

[Tritium]

Just for the record, here is about the best "nearly water thin" epoxy on the planet. Price shows it too.

http://www.conservationresources.com/Main/section_34/section34_21.htm

It would be interesting to vacuum it into the birch but then you are out way more money than pure quasi-isotropic CF.

Thurmond

 

[jhitesma]

Ok, this build isn't done...yet...but I have been a little silent on the latest updates. Partly because I've been busy but also partly due to a request by Twitchity to hold off on sharing some of this

Twitchity gave me the go ahead to finally share this all a few weeks ago but I've been trying to get some more flight video before I wrote it up. Unfortunately it seems like my mobius is cursed and causes quads to crash every time I bring it along - so no video...but if I don't update soon I'll forget the updates I've been meaning to make.

Ok, the full story on why I tried the hybrid arms. As you may remember just before Christmas Balu sponsored a new carbon frame for me on this build. I put that together fairly quickly and loved how it flew. But after the first flights noticed an issue. The arms were falling apart! At first it looked like the ends were just chipping worse than I had expected. But upon closer inspection I saw things were actually far worse, the CF was delaminating big time.

I contacted Twitchity and he ran out to his garage and inspected the sheet of CF the arms were cut from. Sure enough he found that while it looked the same as the past sheets he had used - there was something wrong with it. Tossing a small piece at the floor it instantly delaminated. Twitch was pretty livid about this He contacted the CF supplier and alerted them and they eventually admitted to sending him a piece of "experimental" CF by mistake that wasn't meant to leave the factory. Twitch suspects they were experimenting to find a cheaper way to produce their CF, I'm not as kind and suspect they were experimenting to see if he'd care if they sent him lower quality sheets. The supplier eventually agreed to replace the material for him - but that raised questions about their reliability and got Twitchity questioning if he could trust them and interested in trying other material.

Which was why I pitched in for a sheet of the hybrid material.

While waiting on the hybrid material I kept flying on the delaminating arms. They still worked...but they were getting less and less stiff with every crash. When I finally took them off to install the hybrid arms they fell apart into pieces:



The hybrid arms as I already covered were wonderfully light - but unfortunately after just a few mild crashes the gave in. Postmortem on them looks like the issue was delaminating again - though this time it was the layers of the ply that appear to have delaminated which led to more forces in the outer CF layer which eventually gave in:





I'm kind of impressed with how much they did bend before breaking. I still think they'd be great for a full on racer where every gram counts if you can afford a box of spares...but for my kind of flying - just too easily broken. I still have a full set of them though so maybe I'll do something with them in the future.

The CF manufacturer did finally make good with new material for Twitchity which passed his tests. He was able to replace my CF arms and send out replacements to everyone else who got arms cut from the same bad sheet. Which is why this post has been on hold - he wanted to make sure everyone got their replacements before I shared this with the public.

The new arms are holding up well. They've had a number of good hard crashes in a cinder block wall, my house, my driveway, my street and the field. I'll try to get a video up showing a few of them from the other day including a bounce off rocky terrain that popped it back 3' or so in the air before skidding across pavement, and a dead prop fall from about 100ft up when my PPM wire broke. Maybe I can talk my co-worker into doing a "best hits" compilation from all the crashes I've recorded with it at some point

I got the PPM wire fixed...and given the way I abuse this little quad I finally gave in and accepted that "with age you get a cage" and installed the protective cap Twitchity originally gave me with the first set of G10 parts:






This little guy has far surpassed my expectations overall. The 1806 motors are still the biggest weak spot - though the KISS ESC's have really helped get them to behave at least. I hope to get some 2204's on here once I've got my hex built and a few other projects off the table. For now it's fun and gets attention when people see me flying it - but it does't drop my jaw the way 2204's do

The big concern Twitch and I had were whether the PCB for the PDB would be strong enough in this kind of minimal frame. Given the success of the motowii boards I figured it would be ok - and so far it does seem to be holding up great on this latest v3 revision. The only damage I've managed to do after the upgrade to good CF arms are a few minor chips and scuffs on the ends of the arms from my run ins with pavement and cinder blocks.

I'm still dialing in the tune, I'm currently running a nanowii with MW 2.3 and oneshot it flies great...but I think it still has a bit more in it. Either way it has more in it than my skills can really take advantage of and it's my most reliable go-to fun flier. I can pop 5" props on it and use my "tame" profile then pass it to just about anyone and they can fly it. Or I can put 6x4.5's on it and my acro profile and really have some fun.

 

[cranialrectosis]

I am glad they finally owned up for the CF. I also noted Twitchity updated his signature and no longer has the holidays message up.