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HomeAircraftHelicopterFlybarless Rotor Head SystemsBeastX › Trex 250 woes-cyclic oscillations of death
12-30-2010 04:41 AM  7 years agoPost 1
cudaboy_71

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sacramento, ca, u.s.

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i'm not at my wit's end yet. But, I'm running out of ideas.

I just set up the beastx on my 250 with a microheli head and spektrum satellite. went through the setup routine with little cause for concern.

Here's a rundown of how setup and first flights went:

with the current geometry (stock Align 410 servo horns on the 2nd hole from the end=11mm; grip ball at the outer hole of the grips=17mm) i'm unable to dial in more than 7° of cyclic pitch with 12° of collective. it's not a software issue, i'm just physically at the ends of the throws for the servos. the manual suggests i should be able to achieve 12° cyclic. however, moving either sets of horns to increase throw results in out of spec (purple light) when setting the cyclic range (the step where you set 6° of cyclic).

aside from that single inconsistency, the rest of the setup went according to the manual, achieving blue-led (within spec) setups across the board.even with only 7° cyclic i'd only expect slower than desirable roll/flip rates. as you'll see below, this is not the case.

Also, per the manual i lowered the dial 1 'gain' pot from 100%/mid-dial "a bit" as recommended. this was maybe 1 hour on the clock dial counter-clockwise.

so, i go out for the initial spoolup and pull to a hover. hover was ok, but the tail had significant wag. landed and dialed the gain down from the recommended 'F' setting (which equals ~70 on my 9303) down to 24 before i could hover without a wag. so far so good.

this time after pulling to a stable hover i began rocking the aileron cyclic. first two rocks were good, then i went into a violent control-loop oscillation that would have resulted in either a crash or in-air self-destruction if i were any higher than the 18" where i could safely (and did) hit auto and drop to the ground.

over the course of 8-10 test hops, dialing down pots 1 and 2 to just less than 25% offered no signs of improvement. after achieving hover, a pitch pump combined with any cyclic movement rapidly degenerates to self-destructive oscillations.

in old v-bar parlance this meant the AOF was out of whack. however, i'm not sure where or what to adjust this in the beastx.

the one simple thing i have yet to try is different mounting pads. currently i'm running a thin layer of dense gel directly to the bottom frame of the heli, strapped down tightly with velcro. this method has worked well for every heli i own from 450 up through 700. but, i suppose a little heli like this might need the thick, supplied foam.

i just thought i'd post to see if this rings of any other issue anyone may have run across.

thanks.

if it ain't broke, break it.

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12-30-2010 05:08 AM  7 years agoPost 2
Tail_BoomStrike

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Will you clarify this statment.
Also, per the manual i lowered the dial 1 'gain' pot from 100%/mid-dial "a bit" as recommended. this was maybe 1 hour on the clock dial counter-clockwise
The convention I am familiar with is that looking at the top where the LED's are at, and the servo connection to the left. The factory default position of the pots are at 9 o-clock position, pointing towards the servo connection.

The manual recomends to lower the the swash gain(turn counterclockwise) for helis 450 and smaller.

My first test hop on 450 resulted in violent wobble also, except I forgot to lower the swash gain, it was at 10 o'clock. When I dialed it down to between 7-8 o'clock, that took care of it and never have the slightest issue since.

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12-30-2010 05:19 AM  7 years agoPost 3
cudaboy_71

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sacramento, ca, u.s.

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sure. you summarized the passage in the manual i read pretty well. to quote exactly from page 57:
7.1 Swashplate: cyclic gain (Dial 1)…
…The factory setting for the dial is horizontal which corresponds to 100% swashplate gain. For your first flights we suggest not changing this setting. However, when using very small helicopters (such as 250 or 450 size), reduce the swashplate gain slightly.
the word 'slightly' was the vague word i was referring to. since the pot was horizontal, pointing toward the servo connectors as you said, i turned the pot what i thought 'slightly' should be (about 1 hour on the clock) counterclockwise.

as stated, in repeated test hops reducing this pot to even 6;30 o'clock (just less than 1/2 way between horizontal and vertical) did nothing to prevent the violent feedback loop.

i also tinkered with dial 2 to about the same 6:30 position. but, i could not tell any difference in what flight i could attempt.

if it ain't broke, break it.

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12-30-2010 05:31 AM  7 years agoPost 4
Tail_BoomStrike

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Sorry, I'm not familiar with 250. Seem a lot more people are running MB on 250 at the other forum, with great result. You might get better feedback from them.

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12-30-2010 05:35 AM  7 years agoPost 5
cudaboy_71

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sacramento, ca, u.s.

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thanks. i'm already posted there as well

if it ain't broke, break it.

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01-01-2011 04:59 PM  7 years agoPost 6
jmiles3830

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orlando fl. orange

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BeastX Trex 250 woes-cyclic oscillations of death
what fbl head are you because i have a microheli head on my 250 hitec hs65 cyclic servos. i back off the cyclic gains about a 1/4 turn form center. and my trex250 flies great.

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01-01-2011 08:40 PM  7 years agoPost 7
cudaboy_71

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sacramento, ca, u.s.

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i had to change the geometry of the head to the inner hold on the mH head. it now flies great...thanks though.

if it ain't broke, break it.

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