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Model Forum / Radio Controlled / Helicopters / April 2008Trex 450XL Pitch curve help
I have joined the wonderful world of RC. After much deliberation I chose to go the heli route as I have a big garden and a park cross the road where I can practice. I bought a TREX 450XL CCPM kit complete with Align 450L motor and BL25T ESC. The radio is a Spektrum DX7. Batteries are flight power EVO Lite V2 2500mA. Gyro is the Futaba GY401. Charger is the Swallow Advanced and I have the flight power V Balance. I built up the kit and had it set up by one of the experts from the shop. I have training gear attached. Pinion was a 15T but I replaced it with a 13T. I have been through about 10 battery's so far and I am managing to hover at about waist height for a few minutes at a time. The problem I am finding is I am not getting good battery life. After 6 or 7 minutes the Trex starts pulsing which I am told is the sign that the battery is going flat. If I let the Trex rest for a few minutes (I assume the battery is recovering during this period), I can then take off and hover for a few more minutes. After the batteries cool down, the 2 of the 4 leds on the V Balance fuel gauge light up for each of the 3 cells in the pack. It could be my beginner way of flying, it could be not enough pitch , new batteries, training gear weight, not enough pinion main gear slack etc. etc. What I would like to do first is change the pitch curve. It's in the normal position now with values of L=20.5 (is this too much negative pitch and should I change it to say 50%?) 1=55.5 2=77.0 3=92.5 H=100 Throttle curve L=0 1=20.5 2=43.0 3=69.5 H=100 Am I on the right track? What do you suggest as a first step? > I have joined the wonderful world of RC. > After much deliberation I chose to go the heli route as I have a big [quoted text clipped - 52 lines] > > What do you suggest as a first step? buy a pitch gauge ??  SignatureKevin R Reply address works >I have joined the wonderful world of RC. > After much deliberation I chose to go the heli route as I have a big [quoted text clipped - 52 lines] > > What do you suggest as a first step? When the Trex starts pulsing STOP flying and charge the battries or you will fook them up. For longer flight times use a 11T Pinion, it will do you for just hovering. Next get a pitch gauge Then........ pitch .... Norm. 40 45 50 75 100 Idle 1... 0 25 50 75 100 Idle 2... 0 25 50 75 100 Throttle you will have to play around with depending on what pinion you are using My t-rex 450 is set up like this on 13T Pinion Pitch norm 40 45 50 75 100 idle up 1 0 25 50 75 100 idle up 2 0 25 50 75 100 Throttle norm 0 50 70 70 80 Idle 1 90 85 80 85 90 Idle 2 100 95 90 95 100 I use the same Pitch curves on my T-rex 600e and two t-rex 600n's Have a look at a video called .....Pitch and throttle curves 101 http://www.helifreak.com/showthread.php?t=11373 >> I have joined the wonderful world of RC. >> After much deliberation I chose to go the heli route as I have a big [quoted text clipped - 102 lines] > > http://www.helifreak.com/showthread.php?t=11373 without a pitch gauge any curve numbers are meaningless as you have no idea what the pitch actually is SignatureKevin R Reply address works Thanks for your responses. I will get a pitch gauge. However I am looking for a rule of thumb. For the current battery problem I am facing should I leave the throttle curve as is and just increase the low value pitch to say 50 to give me more lift for the less throttle? >However I am looking for a rule of thumb. The rule of thumb is that the current load goes up as the head speed goes up. >For the current battery problem I am facing should I leave the >throttle curve as is and >just increase the low value pitch to say 50 to give me more lift for >the less throttle? Changing low pitch won't make any difference. You must look at the hovering pitch. To reduce head speed, you must increase hovering pitch and correspondingly reduce hovering throttle. Note that the T-rex 450 does not like a low head speed. It will start wobbling if the head speed gets too low. There was a thread here a few days ago about recommended head speeds. SignatureRoRo > Thanks for your responses. > I will get a pitch gauge. [quoted text clipped - 3 lines] > just increase the low value pitch to say 50 to give me more lift for > the less throttle? these are my setting mine for what its worth are throttle (not so much a curve as a dog leg) mine 0 75 86.5 96 100 yours 0 20.5 43.0 69.5 100 pitch mine 29.6 44 57.5 70.5 82 yours 20.5 55.5 77.0 92.5 100 I think you need to ramp the throttle up a lot quicker and get the head speed up to 2000rpm+, and reduce the pitch, your 1/2 throttle pitch is nearly what mine is at full ,but I only hover and do gentle circuits I seem to remember reading that brushless motors are lot more efficient at higher RPM's SignatureKevin R Reply address works Thanks. I re-adjusted belt and pinion tensions, this along with the change from a 15T to 13T pinion has made a huge difference. I have also increased the throttle pitch but not sure it has done much though. I had a bit of a hard landing yesterday and since then the tail seems to wander quite a lot, almost as if the gyro is not working properly. Not sure if it's due to the hard landing or due to any of the adjustments I have made above requiring re-adjustment to the gyro? > Thanks. > I re-adjusted belt and pinion tensions, this along with the change [quoted text clipped - 8 lines] > hard landing or due to any of the adjustments I have made above > requiring re-adjustment to the gyro? your tail does it gyrate back and forward or keep drifting? SignatureKevin R Reply address works It keeps drifting. I think I may need to reset the Gyro neutral point? >Thanks. >I re-adjusted belt and pinion tensions, this along with the change [quoted text clipped - 8 lines] >hard landing or due to any of the adjustments I have made above >requiring re-adjustment to the gyro? Low head speed = low TR speed. Low TR speed = low TR thrust. I'll say it again. The Trex 450 likes a high headspeed. IMO 2500 is MINIMUM for solid flight and a good holding tail. I run all 3 of mine at 3000 RPM. Dropping from a 15T pinion to a 13T with no throttle curve adjustment will most certainly drop headspeed and TR speed. Thanks very much for the input. Will give all the suggestions a try. >The problem I am finding is I am not getting good battery life. >After 6 or 7 minutes the Trex starts pulsing which I am told is the [quoted text clipped - 7 lines] >fuel >gauge light up for each of the 3 cells in the pack. You're going to kill the packs like that. Once the speed control starts pulsing, you've discharged too far. It's past time to land and change packs. 6 to 7 mins is about the limit for a 450 with 2200 mah cells. Hovering takes a LOT more power than forward flight so you'll probably want to reduce that flight time to 5 or 6 minutes. >It could be my beginner way of flying, it could be not enough pitch , >new >batteries, training gear weight, >not enough pinion main gear slack etc. etc. It's an operational error on your part. Regardless of how the heli is set up, you need to do some tiral and error "homework" to find out how long you can fly and then set a timer on your transmitter to beep when it's time to land. For LiPo packs, you don't want to discharge more than about 80% of the pack's capacity. For example, if you're flying a 2000 mah pack, the most you want to "take out" is 1600mah (1600mah = 80% of 2000 mah) Taking more out risks damage to the pack and reduces the longevity of the pack. If you really discharge the pack, it could swell, overheat and burst into flames. Starting with a freshly charged pack, fly for 4 minutes, then land and let the pack cool. Now recharge it, taking note of how many MAH are put back in. Divide that number by 4 and that'll give you an idea of how many MAH/minute you're taking out. Let's say it's "burning" 250mah/min. 1600/250 = 6.4mins so set your DX7's timer to 6 mins and when it starts beeping, land and change packs. That should keep your packs healthy and long lived. >What I would like to do first is change the pitch curve. >It's in the normal position now with values of [quoted text clipped - 5 lines] >3=92.5 >H=100 Those numbers mean almost nothing without a pitch guage and swash mix percentages. In normal mode on my 450s, I set up for about -3 to +12 on collective pitch, with 0 pitch at mid stick. IDLE 1 and 2 both get -12 + 12. My NOR pitch curve when I was running a DX7 was 0, 42, 50, 75, 100. IDLE were all 0, 25, 50, 75, 100 >Throttle curve > [quoted text clipped - 5 lines] > >Am I on the right track? This was set up by the local "expert"? So at mid stick, he's got it running at less than half throttle and probably 4 or 5 degrees of pitch?? That's a nice way to overload both battery and motor.. The 450 likes a fast headspeed. I run my throttle curve in NOR at 0, 40, 80, 90, 100. IDL1 is 100, 95, 90, 95, 100 and IDL2 is 100 straight across. >What do you suggest as a first step? Find a new expert. :) Head over to www.helifreak.com and register. Once you're there, visit Finless Bob's HeliFreak Tech Room and look for the "450SE and General Build Videos Here" thread. Download the CCPM1 and CCPM2 videos and watch them repeatedly until you understand what's being shown. It will be of immeasurable help to you when you crash and have to set the head up again. In the same forum is Jermo's DX7 video. Download that one too. Those will get you started down the right path. |
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