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Old Nov 23, 2012, 12:42 AM
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Anyway, I am really happy with the RJX 450/500 heads and am only replacing a 450 head after innumerable crashes. Initially with a 3S, then some more with a 6S. It is interesting that the 6S 450 heli crashes with such force. I mean something squared
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Last edited by eagle777; Nov 23, 2012 at 01:50 AM. Reason: Keep on topic
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Old Nov 23, 2012, 06:26 AM
Looptastic!
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Atomic Skull, how is that motor working for you?
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Old Nov 23, 2012, 09:11 AM
just gotta mess with it!
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Quote:
Originally Posted by Atomic Skull View Post
As far as I know they didn't, the angled links on the Trex 500 were designed that way intentionally. One of Finless Bob's videos explains the reasons why the link geometry is the way it is.

http://video.helifreak.com/?subpath=...ame=geo101.wmv



I was wrong about this, the manual specifies 16-16.5mm and I have the balls on the servo horns at 17.5mm (the closest hole to 16.5mm on the horns that come with the 28013's) I guess I misremembered.

Only thing I don't like about the RJX head is that the swashdriver arms use an oddball sized bearing that's very difficult to find. The only place I've been able to find the 3x7x2.5 flange bearings it uses are from China based sellers on ebay. Replacement arms cost $22 from Helidirect or $10 from Hobbyking. Interestingly the replacement pitch arms are actually cheaper from Helidirect than from Hobbyking.
Thanks again for taking the trouble to post the pics and do the measurements, and thanks also for the link to the Finless video, which I will take a good look at! I love his build videos, though it took me a while to get used to his manic hand movements!

So if you had used 19mm servo arms, the angle of the lower links would be quite severe. You must be running the servos pretty close to their mechanical limits at full combined collective and cyclic though, so that emphasises the importance of minimising the use of sub-trim either in the TX or the FBL controller. On my 450 with the RJX, I could only just get -12 +12 on collective and 7 cyclic using 13mm servo arms - so the grip arm/servo arm ratio was 22/13 = 1.69, which is fairly comparable to 29/17.5 = 1.66. In my CX controller, I had to set the collective range to 78, which is on the high side of optimal.

Regardless of the theory above, however, it's good to know that your 500 is flying well, and that things actually work in practice!

I'm looking to get a HK500TT FBL, but as is my normal MO, I obsess about the mechanical setup first! I'm also holding back since HK have been terrible with their shipping lately, and HiModel seem to be a very competitive source for quite a few components, including their 80A ESC's (which Turnigy re-brand as YEP) The HiModel ESC still has the additional programming lead, however, at least according to their product pics.
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Old Nov 23, 2012, 01:37 PM
just gotta mess with it!
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OK, I finally managed to download the Finless vids. My internet connection has been rubbish this morning!

I can see what Bob's on about, and sure, you will get less interaction at higher collective - but the adverse effect of that is that interactions will be increased at negative pitch. I don't really see the sense of that, since my aim at least is to fly as comfortably inverted as right side up, and to that end I think the heli response should be similar inverted and upright.

With the FB head, the swash to mixing arm links are more or less vertical. With an FBL head, however, the longer grip arms always result in the upper links splaying outwards. As I said previously, this causes pitch differential, but in the opposite sense to the differential introduced by the angled lower links, so I reckon things more or less cancel out.

It's easy enough to work out the collective pitch you get with any given collective servo movement, given the dimensions of the swash, servo and grip arms and link lengths, but much trickier to add in aileron and elevator at the same time. For collective only movements, I draw the linkage in 2D in AutoCAD. For combined collective and cyclic, I have to draw it in 3D, which is no big deal, but then use a method of successive approximations to find the resulting blade pitch - and that is very tedious indeed!

Wish I could CNC my own frames though!
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Old Nov 24, 2012, 12:07 AM
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Quote:
Originally Posted by 2Doggs View Post

I can see what Bob's on about, and sure, you will get less interaction at higher collective - but the adverse effect of that is that interactions will be increased at negative pitch
No it's exactly the same in negative pitch as it is in positive pitch.
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Old Nov 24, 2012, 09:24 AM
just gotta mess with it!
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Originally Posted by Atomic Skull View Post
No it's exactly the same in negative pitch as it is in positive pitch.
It can't be. The way Bob describes the effect is that it makes the links squarer to the servo arms at more than 50% collective. Therefore at less than 50% collective, the links will be at a more acute angle.

It's surprising that helis fly as well as they do, bearing in mind the amount of interaction you get with cyclic input at high or low collective.
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Old Nov 25, 2012, 06:03 PM
Just fly
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Australia, VIC, Glen Waverley
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I had my first real failure on the HK500 yesterday.

Took the heli out for a quick fly as I needed some R&R from all the house painting I have done all week.

Anyways, all was good for the first 2mins. Did some fast fig. 8's, loops and hover inverted. Once I got out of my inverted hover the motor just stopped and you could hear the blades slowing down. I quickly put my auto rotation plan to work and dumped it into full neg from 15mt high and just before hitting the ground positive pitch to soften the landing. It landed a little hard on the landing gear, but no damage to anything.

I sat there looking at the heli and thought what just happen..... Then I saw smoke coming out of the canopy!!! I run to the heli thinking my lipo is about to blow. Removed the canopy, disconnected the lipo and pushed it well aside from me. The lipo still had alot of charge so I wasnt taking any chances.

After a further inspection it ended up being the HK SS serise ESC that was gone. Must have been very hot as the solder on one motor wire was disconnected from the board & sections of the heatshrink were gone and the now black internals are showing.

I believe I had a very small fire that could have been alot worse.
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Old Nov 25, 2012, 06:13 PM
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Glad to hear it was not any worse, and good job bringing her down!
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Old Nov 25, 2012, 06:30 PM
Just fly
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Thanks mhills

I'm a little annoyed that it happen only 2min into my first pack of 4. Still I'm happy about the failure (finally a real one) and how I managed to control it. If I was inverted and any another position other then normal I may not have been so lucky.

Now the only heli I have going is the mcpX. 450 is down & I cant be stuffed working on it, 500FB down from dead speedy, 500FBL currently building & 550 currently building. All these helis and only one working.. hahaha.

I just got a package today... RJX FBL head for the 500.. very nice quality and the t600-1100kv motor for the 550.
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Old Nov 25, 2012, 06:39 PM
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I went into debt this weekend with all the blackfriday deals and all on helicopter parts lol! Don't know what I'm going to do about Christmas.
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Old Nov 25, 2012, 06:48 PM
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whats blackfriday?
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Old Nov 25, 2012, 07:18 PM
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http://en.wikipedia.org/wiki/Black_F...%28shopping%29

Nice save on your 500 also
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Old Nov 25, 2012, 07:20 PM
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Don't forget Cyber Monday. http://en.wikipedia.org/wiki/Cyber_monday

We love to spend (some (half) of USians).
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Old Nov 25, 2012, 07:22 PM
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And Small Business Saturday. Heh. Probably something for Sunday now, or soon. I haven't heard of it.

http://en.wikipedia.org/wiki/Small_Business_Saturday
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Old Nov 25, 2012, 07:36 PM
Just fly
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haha.. sound like any excuse to spend or have a party or public holiday
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