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Old Feb 11, 2011, 09:30 PM
The New Guy
fatalsync's Avatar
USA, TX, College Station
Joined Oct 2010
134 Posts
Quote:
Originally Posted by skyeblu View Post
Is your motor running right direction
Yes, head is clockwise and tail is counter-clockwise. At low headspeed, the tail works properly, but at higher headspeed the tail doesn't seem to be able to keep up with the motor torque.

I have the Turnigy 2836 motor with 11t pinion, 25C battery, and a 30A ESC. The bird lifted off fine before the crash, so I don't think it's electronics and I think I either screwed something up mechanically when I put it back together, or I jacked something up in the TX settings.
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Last edited by fatalsync; Feb 11, 2011 at 09:35 PM.
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Old Feb 11, 2011, 09:33 PM
The New Guy
fatalsync's Avatar
USA, TX, College Station
Joined Oct 2010
134 Posts
Quote:
Originally Posted by Harrow View Post
fatal sync,

Sounds like you might not have adjusted your links correctly after your rebuild. Have you checked the blade pitch with throttle stick movement? Are you getting 0 degrees pitch at mid throttle stick and 9 or 10 degrees pitch at full throttle stick?

Then again, if your tail is also spinning, then you may have too little head speed.

Check your main blade pitch first. If that is correct, then head speed is the only thing that would stop if lifting off. If you then need to increase head speed, that may fix your tail problem.
I lowered the max pitch based on some beginner settings I found on Helifreak to around 6 degrees. I just set everything back to full range with a linear pitch curve from -10-0-10 so I'll try it out tomorrow and see if that makes a difference.

I need to fix the tail though before I let it off the ground... if my headspeed is too low, why would it work fine up to about 3/4 throttle?
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Old Feb 12, 2011, 01:12 AM
Yes, I know it's upside down.
Sydney, Australia
Joined Dec 2008
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Quote:
Originally Posted by fatalsync View Post
I need to fix the tail though before I let it off the ground... if my headspeed is too low, why would it work fine up to about 3/4 throttle?
With low head speed, below 3/4 throttle you still have the weight of the heli holding it firm on the ground. Then, because your head speed is low, you need a lot of pitch to begin getting any left. For sake of argument, let's say you need 8 degrees of pitch to start getting lift with your lower head speed. At this point, you start to get some lift, but with all that pitch, you are getting more and drag on the blades. So, above your 3/4 throttle point, less weight on the skids, heaps of drag on the blades, but a tail that is spinning way too slow to counter act the main blade torque. It's a classic scenario.

Do you have a way of measuring your head speed?
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Old Feb 12, 2011, 07:21 AM
The New Guy
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USA, TX, College Station
Joined Oct 2010
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Quote:
Originally Posted by Harrow View Post
With low head speed, below 3/4 throttle you still have the weight of the heli holding it firm on the ground. Then, because your head speed is low, you need a lot of pitch to begin getting any left. For sake of argument, let's say you need 8 degrees of pitch to start getting lift with your lower head speed. At this point, you start to get some lift, but with all that pitch, you are getting more and drag on the blades. So, above your 3/4 throttle point, less weight on the skids, heaps of drag on the blades, but a tail that is spinning way too slow to counter act the main blade torque. It's a classic scenario.

Do you have a way of measuring your head speed?
OK thanks.

I actually just got an optical tach, but I need to rig up a clamp stand before I try to use it.
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Old Feb 12, 2011, 01:55 PM
The New Guy
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USA, TX, College Station
Joined Oct 2010
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So... I'm stupid.

One of the blade grip links had apparently come off. Clipped it back and on no problems.

According to my tach the headspeed is insane over, 4000 before even approaching full throttle. That can't be right.
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Old Feb 12, 2011, 01:58 PM
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Toronto (Don Mills), Canada
Joined Dec 2002
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You might be reading both the blades and the paddles, which will double it.
Make sure to read it far enough out, and under natural light. AC light will give wrong numbers.

Pat MacKenzie
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Old Feb 12, 2011, 02:06 PM
The New Guy
fatalsync's Avatar
USA, TX, College Station
Joined Oct 2010
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Quote:
Originally Posted by pmackenzie View Post
You might be reading both the blades and the paddles, which will double it.
Make sure to read it far enough out, and under natural light. AC light will give wrong numbers.

Pat MacKenzie

Good point, I didn't think about the blades doubling it since I put the reflective tape on just one blade. Definitely past the paddles though. So it's probably about right when 1/2ing it. I'll take another reading with that consideration.

The tach I have projects a laser dot that it reads so I don't think the lighting would affect it. Doesn't say anything about it in the manual.
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Old Feb 12, 2011, 02:42 PM
just gotta mess with it!
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North West Louisiana
Joined Nov 2009
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Hover at mid stick?

With your 2836, which is 3700Kv, and an 11t pinion, you should be getting up to HS 3000 with a full battery pack, dropping to 2600 at the end of the battery (assuming it's a 3s pack, which I'm sure it is!)

So for learning, that's plenty - I would even go so far as to suggest you could use a 10t pinion, but with 11t you could limit the throttle to less than 100% to keep the HS around 2600 or so. I trust you are not using woodies - I believe they're only rated for 2200.

For learning, you might want to set up the normal curves so that hover is at mid stick - otherwise, with zero pitch at mid-stick all the action happens in a very small range of stick movement around the 3/4 position. If you do choose to set the normal curve for hover at mid stick, you can make the heli very gentle to hover by having full collective give only +3 pitch from hover, and full low -3 from hover - so the total pitch range in the normal curve would be about +3 to +9. If you set your swash mix to give you -10 to +10, then the normal pitch curve would be a straight line with your low point 65% and your high point 90%. If you then find that the hover is above the mid stick position, you can add the same percentage to all the points and if it's below mid stick, subtract the same percentage from each point. Using that kind of pitch curve with such an expanded stick movement around the hover will make the heli less likely to shoot up from a hover which can lead to over-correction and the dreaded pilot-induced-oscillation! Your throttle curve to go with that normal curve would start at 0% but then be fairly flat, maybe 70% to 80%. You need to get used to setting the heli down with the HS staying fairly constant, rather than by the headspeed dropping right off.

Edit update: just tried this out on my driveway, and with my 450 using governor mode for HS about 2700, hover was at 70% - so a normal pitch curve of 50% low, 70% mid stick, 90% high felt very soft. 60 - 70 - 80 was super soft! You wouldn't want to fly around on a windy day with that kind of normal curve, though - you'd have trouble getting the heli down! It's for hovering practice only!
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Last edited by 2Doggs; Feb 12, 2011 at 03:13 PM. Reason: Edit: oops, corrected pitch percentages!
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Old Feb 12, 2011, 03:16 PM
The New Guy
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USA, TX, College Station
Joined Oct 2010
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I have the Align 325 Pro woods on, supposed to be good to 2800.

Thanks for the tips I'll try out your curves. How much expo should I use? I've read -30%...

Looks like I'm getting about 2700RPM at 80% throttle.
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Last edited by fatalsync; Feb 12, 2011 at 03:24 PM.
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Old Feb 12, 2011, 03:25 PM
just gotta mess with it!
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North West Louisiana
Joined Nov 2009
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Expo

There's no expo on collective pitch, so you need to rely on soft curves to make it gentle. If you start with 30% expo on rudder, aileron and elevator, make sure the expo is going the right way! On my JR 9XII, (9303), you can see a graphical representation of what the expo is doing, and on the JR at least, it's +ve expo to soften things up. I generally use +0% to +15%, but 30% might be good for learning.
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Old Feb 12, 2011, 04:56 PM
I don't want to "Switch Now"
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Toronto (Don Mills), Canada
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Futaba negative expo is the same as JR positive expo.
I like about 20-30% in the direction that softens throws near neutral. Depends on how much cyclic swash travel you have.

Pat MacKenzie
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Old Feb 12, 2011, 05:49 PM
The New Guy
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USA, TX, College Station
Joined Oct 2010
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Success! Thanks everyone. Got a few 30+ sec hovers out of it.

Seems to want to drift back and to the left naturally on lift off. According to Radd's the drift to the left is natural, so I was expecting that, but I feel like I'm having to give it a little too much forward cyclic to keep it level.
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Old Feb 12, 2011, 05:54 PM
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Canada, ON
Joined Mar 2010
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I use a laser tach as well, and find it a lot easier to put the reflective tape on the motor instead of the blades. With an 11T pinion on a 450, just divide your reading by 13.64.
Not only is it safer, since you don't have to reach over or under the blades, it's also easier to aim the laser.
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Old Feb 12, 2011, 06:13 PM
The New Guy
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USA, TX, College Station
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I rigged up a "tank" for the heli, with plywood shielding on all the sides so I could spin it up and hold the tach over the blades.
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Old Feb 12, 2011, 07:20 PM
just gotta mess with it!
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North West Louisiana
Joined Nov 2009
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Quote:
Originally Posted by fatalsync View Post
Success! Thanks everyone. Got a few 30+ sec hovers out of it.

Seems to want to drift back and to the left naturally on lift off. According to Radd's the drift to the left is natural, so I was expecting that, but I feel like I'm having to give it a little too much forward cyclic to keep it level.
In a hover, to balance the tail rotor thrust, the heli (with a clockwise main rotor) has to lean slightly to the right - so lifting off dead level will always result in a drift to the left, even with a heli that's set up perfectly.

And congratulations on the hovers!
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