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HomeAircraftHelicopterHIROBOHirobo SDX › SDX flaw?
08-03-2009 01:47 PM  8 years agoPost 21
gouki

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philippines

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i have the impression that the bending of the blade bolts were from the pull of the cf blades together with sudden and quick change of angle from doing 3d. and that the blade bolts aren't that hard since hirobo has the same blade bolts but hardened versions. with the blades bolts bent, my tracking was off and there was vibrations on the pod which is never good for helis

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08-03-2009 06:48 PM  8 years agoPost 22
John Benario

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Las Vegas

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Blade bolt bending is caused by the centrifugal pull of the blades exceeding the allowable stress in the steel. I don't have an SDX to look at, but 4 mm bolts are definitely strong enough for a 50 size model. If the bolts are bending the steel is too soft.

Again, I don't know what the SDX comes with, but make sure to use shoulder bolts with the shoulder extending fully between the blade grip tongues. If Hirobo does not include bolts like that then it may be that they were simply trying to save money and using substandard hardware.

Kind of like including washers in the Turbulence that won't fit over the bolts that they are supposed to fit over!

John Benario

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08-05-2009 12:03 AM  8 years agoPost 23
Leif

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USA

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Look at the design of the SDX blade grips for the FZ-V head.

To accomodate the larger diameter bearings, by design the SDX blade grips have a wider grip distance then the Sceadu.

The grips use extra blade spacers to accomodate standard 12mm root thickness blades. Due to the wider grip distance and use of spacers, the blade bolts are spanning a significantly larger distance than they would with grips that have a natural 12mm opening. I haven't measured the spacers, but they appear to be in the 2-3mm thickness range. Looking at the bearings that need to slide into the grips, they are 16mm OD, which means that the bolt is probably spanning 16mm compared to the 13mm span on the Sceadu (keep in mind that the Sceadu grip also has a groove in it to provide clearance for the bearing OD).

I believe that the extra distance is probably too much, and that the standard grade M4x35 bolts simply can't take the lateral forces over the increased distance. The hardened drag bolts would be a highly recommended upgrade for hard flying. I've used these for years on my Evos.

2532-044 Drag Bolt M4x35(Hardened)

Leif

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08-05-2009 05:12 AM  8 years agoPost 24
gouki

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philippines

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the hardened drag bolts 2532-044 just arrived today and i quickly noticed it has a different shape a little bit and that it seems to use the 2.5mm hex drivers as opposed to the 3mm that the stock blade bolts require. i hope the weather improves soon so i can try putting my sdx through its paces using the hardened drag bolt. from the looks of the drag bolt, i am confident it will hold up. still, no harm in keeping my fingers crossed

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08-05-2009 06:19 AM  8 years agoPost 25
gouki

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philippines

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i was wrong about needing the 2.5mm hex driver instead of the 3mm. it still uses the 3mm hex driver. the head of the drag bolt is a tad thicker than the stock blade bolt that's why i had the impression the socket was smaller in size. even the body of the drag bolt was a little thicker than the stock bolt. it still fits the blade bolts and fits snuggly on the spacers. that's good i think as there will be less play available using the hardened drag bolts

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08-05-2009 10:58 PM  8 years agoPost 26
davidevo50

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Montreal, PQ, Canada

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I just replaced the drag bolts on mine as well... The factory ones were in pretty bad shape(20 flights)! But hey, I still love my SDX and Hirobo!

LIVE IN THE NOW!

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08-06-2009 03:56 PM  8 years agoPost 27
kej

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Denmark

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my bolts are also bent after maybe 30-40 flights.

Kim Jensen

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08-06-2009 05:50 PM  8 years agoPost 28
John Benario

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Las Vegas

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This is interesting reading. Hirobo went to a 10 mm spindle as an "upgrade" to a 50 class helicopter. But now there is an issue in that the wider blade tongue spacing combined with the comparatively thin blade root of the 50 class blades is causing an issue.

The centrifugal force of the blade now seems to be concentrated too far away from the blade tongues so the bolts are failing in bending. I said 4 mm bolts are strong enough for 50 class blades, and they are in shear, which is what the applied load is when the blades fit in the blade grip with no spacers.

Unintended consequences.... helicopter design is rife with unintended consequences.

So which is better, the 10 mm spindle in the Hirobo or the 8 mm spindle in the Align????? I would guess the folks would bent blade bolts have an opinion on that.

The solution is going to be a new blade grip which has integral stepped down portions at the blade tongue ends so the blades fit in with no spacers. Unfortunately that is going to be one hell of a part to make, even on CNC machines. Maybe Terry Moore can offer an opinion on whether is possible.

If it is it will be a very expensive part, no doubt. Can somebody post a close up picture of a blade grip with no bolt in it so I can see if it possible to modify the grip for a 5 mm bolt. That will be the quickie fix.

John Benario

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08-06-2009 10:19 PM  8 years agoPost 29
davidevo50

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Montreal, PQ, Canada

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I don't see why there should be a new design if the hardened drag bolts are strong enough to take the stress... We'll see soon enough the weekend is almost here.

LIVE IN THE NOW!

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08-07-2009 02:47 AM  8 years agoPost 30
Leif

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USA

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The blade grip holes are similar in design to those of the Sceadu. They have the hex countersink to accomodate the M4 nuts on either side of the grip. It would be fairly easy to enlarge the bolt holes to accomodate M5 bolts, but then you would also need to drill out the blades themselves since very few 600mm class blades are drilled for M5 bolts.

The hardened M4 bolts should do the trick. The unsupported span appears to be only 3mm longer than the grips on the Evo 50.

Maybe a better design idea would be to provide some kind of keying system between the grips and the spacers to allow the spacers to take some of the lateral force off that part of the bolts. The current design lets the spacers float, so they provide no support against lateral stress on the main axis.

Leif

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08-10-2009 06:09 PM  8 years agoPost 31
John Benario

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Las Vegas

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I noticed this past weekend, the Align blades have a 5 mm hole. I will be building an SDX in the coming months, and if the blade bolts bend I will try the 5 mm bolts.

John Benario

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08-10-2009 10:14 PM  8 years agoPost 32
payne1967

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uk

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the trex 600 runs 4mm bolts
the 700 runs 5mm bolts

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08-10-2009 10:27 PM  8 years agoPost 33
hootowl

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Garnet Valley, Pa.

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There are a few helis out there where bending of blade bolts was reported. I have never heard of broken blade bolts. Sometimes a softer bolt that spans a large distance will bend. Personally it would not deter me from purchasing the heli. 4mm bolts can more than handle the load. The bending can be reduced by tightening a little more than you normally do. In the end you can beat the crap out of it but you will never see a blade fly because of a slight bend in the blade bolt.

Engineering...

Bending is almost always better than breaking. Airplane wings are constantly bending and never breaking. Sure they (wings) don't stay bent but trust the engineering. 4mm is plenty!

Wolves don't lose sleep over the opinions of sheep

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08-12-2009 03:32 AM  8 years agoPost 34
gouki

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philippines

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i finally got to try out my sdx yesterday using the new hardened drag bolts. i flew three tanks and did my usual flying to see how the hardened bolts will hold up. after flying, the drag bolts were bent not as bad as the stock blade bolts and not that noticeable but it is still bent turning the drag bolts, you can see a slight wobbling and looking at it from the bottom-up of the bolt, the bending of the bolt can be seen since it isn't that bad, i will try to check later if the blade tracking is off.
what did you guys use and how did it hold up? i forgot to mention i am using 610mm rotortechs, maybe using radix 600mm sb which is a tad shorter and lighter will prevent the bolts from bending?

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08-12-2009 04:46 AM  8 years agoPost 35
Henrik Engert

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Cedar Park, TX

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How in the world do you bend them? I have never experienced this, but then again, I do not fly so hard.

Hirobo XSpec EVO
Hirobo SDX
Futaba 12Z FASST

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08-12-2009 04:56 AM  8 years agoPost 36
gouki

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philippines

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i try my best to fly the heck out of it i like to do fast forward flights and do quick and abrupt change in directions. i basically bang the sticks

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08-12-2009 08:10 PM  8 years agoPost 37
Lewd Skywalker

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Manila, Philippines

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What's your headspeed?

I managed to bend those hardened drag bolts in my old Sceadu Evolution, but that I was running more than 2,000rpms and using really heavy glass blades.

SDX FBL | Eagle3 SWM | Trex 600EFL Pro

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08-12-2009 08:43 PM  8 years agoPost 38
watersteps

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Manchester Pa. USA

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Drag Bolts
You may want to install the bolts and then remove them and see if you are bending them when you tighten them down. It takes a lot of pull to bend a hardened bolt, are they realy hardened? Take a bolt about 4 mm x 28 mm, lay it on a hard surface, not your dining room table, lay a 6 inch screw driver shaft across the bolt and press down with both hands. Did it bend? Unless you weight over 400lbs it should remain straight.

watersteps,

If you're gona be dumb, ya gotta be tough! They call me HULK!

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08-13-2009 03:52 AM  8 years agoPost 39
gouki

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philippines

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i can only really guess what my headspeed is until i get my hands on a tach. i set my gov to 1950 on idle2 but since the gov doesn't have 8.7gearing, i can only guesstimate
i can't see how i can bend the drag bolts during installation and removal since i don't really tighten it hard and it goes thru plastic mostly. i installed and removed it a couple of times before flying with it to see how it fits because it was a bit thicker than the stock bolts. i trust hirobo and if they say it's hardened, i believe it is so the hardened bolts doesn't even look identical to the stock blade bolts and although it still bent, it didn't bend as bad as the stock bolts. i will try to bend it with my weight, but only after i get a new set

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08-13-2009 04:29 AM  8 years agoPost 40
gouki

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philippines

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i was recently told how to compute for my headspeed. my headspeed is almost at 2000, it was at 1972-1995rpm

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