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Old Oct 17, 2006, 05:59 PM
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Quote:
Originally Posted by Jeremy Z
You know, I think they just copped the landing gear bracket from the MiniMag
I bet you're right. An afterthought, as I surmised...
Quote:
Originally Posted by Jeremy Z
Another thing to watch for is friction in the pushrod tubes going to the tail.
On my TS-II, most of the friction comes from the sideways motion of the pushrod wire near the servo horn - the tubes don't let it move sideways, but as the horn moves through an arc, the wire has to move sideways a bit. Cutting the plastic tube (snake) back a bit further from the servo decreased the friction a fair bit.
Quote:
Originally Posted by Jeremy Z
I was happy to see that MPX included proper hinges on this plane, and that they did a good job of the tail wheel design.
Nice joiner for the two elevator halves, too. No flimsy, floppy wire here - that plastic tube should make for a really nice rigid coupling.
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Originally Posted by Jeremy Z
Keep an eye on the amount of current your BEC will need to supply.
Yeah, I'll probably use a switching BEC. On a model of this cost, it seems well worth it as extra safety insurance.
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Originally Posted by Jeremy Z
Since you were mentioning putting the servos close to the tail
That wasn't me...

I've moved the servos back on other models (Formosa, for one, and perhaps the Ultrafly Ultimate Bipe). But the AM has a long tail moment and I agree it might be hard to locate the CG correctly if the servos are moved back significantly.
Quote:
Originally Posted by Jeremy Z
...OR Use your 2 lb. inrunner with planetary gearbox.
You mean the one that was LIGHTER than your Power 10?
Quote:
Originally Posted by Jeremy Z
don't forget the 17" prop!!
Would you still snicker as hard if I told you a 17x13 prop would produce about 25 ounces more thrust than an 11x6" prop, while loosing only a couple of mph in pitch speed, using the same power from the motor as the 11x6 prop?

Of course a 17" prop isn't practical on this model, but this illustrates how much efficiency is thrown away by going to a smaller prop. 25 oz is about 3/4 of the weight of the Acromaster - and all that free thrust is thrown away by the 11" prop!

I think a 13" or 14" prop is entirely feasible on the Acromaster. Even a 13" prop gains you about 10 ounces of thrust over a 11" one, for the same power and pitch speed (that requires a 13x8 vs a 11x6 prop). A 14x10 would squeeze out another four or five ounces of thrust.

Notice that I'm increasing the prop pitch as the diameter goes up - this is the secret to keeping the pitch speed up, and not letting it decrease as the prop size goes up. (Edit: I want to make it clear that the motor and/or gear ratio would need to be changed for these bigger props. I am not suggesting slapping a 14x10 prop on the stock Himax motor, that would burn out the motor immediately.)

Obviously APC doesn't make 17x13 prop, but they do make a 13x8 and a 14x10. On the right geared motor, either would be a substantial improvement over a 11" prop (who doesn't like 10 - 15 oz more free thrust?).

Of course, getting that free thrust requires using a different motor, and that motor will cost more than the Himax, and so in a sense that extra thrust is not entirely free.

Is it worth it? That's up to the individual.

-Flieslikeabeagle
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Old Oct 17, 2006, 06:06 PM
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Mike, you're welcome!

Yup, gasoline still packs more energy per pound than any electric batteries I know of. Wonderful stuff, that's why it drove the last century of Industrial Revolution. But there are downsides...the foul grey stuff that passes for air in LA county reminds me of that daily. Not to mention all those folks dying in Iraq.

-Flieslikeabeagle
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Old Oct 17, 2006, 06:50 PM
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oww, a political zinger...

no, but you're right. LA, huh? see you at Apollo field on the weekend?
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Old Oct 17, 2006, 08:10 PM
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Apollo field huh? I go their almost daily. I have been avoiding the weekends, but will soon be there on the weekends due to time change with my new AM! I also fly EZ star with lights / gas planes / and slow stick.
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Old Oct 17, 2006, 09:08 PM
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Vantasstic's Avatar
Las Vegas, NV
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Wow, I just had a great idea for the landing gear on the AM...okay, it really wasn't right now, but while spending some quality time in the bathroom. Beagle, I'm surprised you didn't mention this since we just PM'd about it for the TS II. If the stock landing gear is to flimsy, why not replace it with some plug in, more robust (I hope) landing gear. There would be some additional weight penalty maybe, but it's a thought. Instead of trying to explain it in a word picture; take a look at this link: http://plawner.net/4/twinstar/bill_g...star_bill.html And a little more detailed pictures of the arrangement here: http://www.rcgroups.com/forums/showp...postcount=2297

I just picked up the hardware to do this to my TSII. I'll have plenty left over material to do the same with the AM (when it arrives). Comments on doability?
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Old Oct 17, 2006, 10:02 PM
Flyin' Ryan
USA, MO, Lee's Summit
Joined Sep 2001
980 Posts
I can't imagine putting a Power 25 on the AM. It is way overpowered with the power 10 (very similar to the himaxx 3516-1130). I have to agree with Jurgen that you are adding weight and undue stress to the airframe. I can understand using existing equipment, but I think the plane flies great with the recommended equipment. I have nothing but good things to say about the AM now that I've gotten used to it, and strengthend the LG. It has been a blast.
Ryan
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Old Oct 17, 2006, 10:37 PM
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Skiermike, resedaguy, I don't make it to the Apollo field very often - I usually fly at Brookhurst Park, right outside the Rose Bowl in Pasadena. The AM is big enough that I'd have to be very confident the field was deserted before I'd fly it there, though. Mebby I could come down to the Apollo XI field some weekend just to say hi to you folks in person, and if I have my AM done by then, it would be fun to all three AM's in one place.

Vantasstic, Fantasstic idea.

It never occurred to me to re-use the TSII LG method on the AM, but I think you have a very good point: the TS-II is about the same weight as the Acromaster, made of the same foam, and lands at about the same speed. So any LG design that works on the TS-II should work just fine on the AM as well.

Of course, there's no particular point to having the AM main gear removable (the tail wheel is permanent, unless someone comes up with a new mod). Also the brass tube and sheet do have one disadvantage - they're surprisingly heavy, brass being a pretty dense material.

I had been thinking along the lines of using a traditional torsion-bar type landing gear, which has served the glow RC pilots well for decades - and most glow planes are considerably heavier than the AM and need a well designed landing gear setup. Perhaps something built out of ply and sandwiched into a slot in the AM fuse.

I can't find a good link to show a torsion bar landing gear setup, but this review has some photos and a brief description of one: http://www.masportaviator.com/ah.asp?ID=79&Index=1

-Flieslikeabeagle
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Old Oct 17, 2006, 11:01 PM
'FPV'er...not a "LOS'er
Vantasstic's Avatar
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I haven't built the gear for the TSII yet so I don't know what kind of additional weight it would add. I was thinking the AM fuse isn't all that wide so maybe the total weight wouldn't be all that bad. Not having an AM in hand yet I'm only guessing at this stuff. The torsion gear you mentioned ought to also work, but with maybe the same weight gain?
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Old Oct 17, 2006, 11:26 PM
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Vantasstic, my TS-II originally weighed 33 oz, ready to fly without landing gear. I made three changes - I went to heavier Graupner (glow-engine) counter-rotating props, I switched from a 2000 mAh 3S 10C lipo to a newer 2100 mAh 3S 15C lipo, and I added the landing gear. After that, the plane weighed about 39 oz, IIRC. So I gained six ounces between the three mods. My guess is 3 or 4 of those ounces came from the brass/music wire LG.

You're right, the AM isn't very wide (though probably twice as high as the TS-II!). I don't have a good idea what the torsion gear LG would weigh - certainly I wouldn't save any weight in the actual wheels or music wire, so any weight savings would come down to the brass tube vs the wooden structure for the torsion bar LG. Perhaps you're right, and there would be no significant weight savings at all.

I just pried apart the two fuse halves on my Acromaster kit, and there is a lot of foam around that LG mount area - one could recess a plywood LG mount two or three inches deep into solid foam, if desired.

It would be nice to have a way to make LG from carbon fibre tube, that would be quite a weight savings. I've seen one guy do it, maybe I should ask him for tips. (Sure, you can buy CF landing gear, but they don't have much fore-and-aft give to them, and so I'm not a huge fan.)

-Flieslikeabeagle
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Old Oct 17, 2006, 11:50 PM
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Quote:
Originally Posted by skiermike123
...
I was looking at my batteries and they report a 55A continues and 80 burst.
...
btw, I get almost 10 minutes per battery and they're only 2200 mAh. Go figure.
Well, first you told us you had a 3s 2300mAh pack with 57A bursts, now we have a 2200mAh with 80A bursts. This makes a huge difference!

If you get 10 minutes on 2200mAh, your average current is only 13.2A. Your weakest link is now the heavy motor.

Jürgen
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Old Oct 17, 2006, 11:55 PM
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Are the struts or the mount the weak point?? I know the struts are flimsy, is the mounting method weak also??

I was thinking of designing a nice light carbon gear for it....

Brian
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Old Oct 18, 2006, 12:02 AM
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Quote:
Originally Posted by flieslikeabeagl
...
Would you still snicker as hard if I told you a 17x13 prop would produce about 25 ounces more thrust than an 11x6" prop, while loosing only a couple of mph in pitch speed, using the same power from the motor as the 11x6 prop?
...
On the right geared motor, either would be a substantial improvement over a 11" prop (who doesn't like 10 - 15 oz more free thrust?).
...
Is it worth it? That's up to the individual.

-Flieslikeabeagle
These kind of ideas are the result of using theoretical calc programs wihout knowing their limitations. What do you think a prop of that size would weigh, the gyroscopic forces doing aerobatics and how sluggish the motor would respond when you want rapid rpm changes doing 3D? Think about it.
...
The reasons why the geared motor is usually not better was already posted here:

http://www.rcgroups.com/forums/showp...&postcount=730

http://www.rcgroups.com/forums/showp...&postcount=731


Jürgen
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Old Oct 18, 2006, 12:41 AM
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Brian, I haven't built my Acromaster yet (not even started), but the little plastic trapezoid that carries the LG is quite small - the widest side is maybe 2 1/4", the other dimension about 1.5".

In my opinion, that is simply too small for a robust attachment to something as flimsy as Elapor foam. Foam is weak, and the only way it will survive is the force per unit area is kept down - in short, the force from the landing gear should be spread out over a much larger area.

The wire might well be too weak too, many others say it is. But even if the wire were strong enough, I think that plastic trapezoid is too small.

I no longer see Helig's posts, but I bet I can guess whats in his latest. Maybe it's "The stock landing gear designed by Multiplex is perfect".

Or perhaps it's "the motor and prop recommend by Multiplex is perfect".

Did I get anywhere near close?

-Flieslikeabeagle
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Old Oct 18, 2006, 06:36 AM
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Jeremy Z's Avatar
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[quote=Would you still snicker as hard if I told you a 17x13 prop would produce about 25 ounces more thrust than an 11x6" prop, while loosing only a couple of mph in pitch speed, using the same power from the motor as the 11x6 prop?[/quote]Yes, I would, because you're going to need to add more weight (in the form of a gearbox) to get that. Also, you lose efficiency in the gearbox. If it were as simple as you make it sound, the designers would've thought of it. You're not the ONLY smart person around, you know.

Jürgen made a good point earlier about planetary gearboxes making heat and not necessarily being designed for continuous duty.

I guess you could find an unusually efficient open gearbox to work with that mount somehow. Or are you going to redo the motor mount too?

I have to admit, I'm curious to see if you're going to put your money where your mouth is with regards to the power system, or leave it as a theory.
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Old Oct 18, 2006, 12:32 PM
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Originally Posted by Jeremy Z
Yes, I would, because you're going to need to add more weight (in the form of a gearbox) to get that.
Usually an inrunner of equal power is considerably lighter than an outrunner. That usually means you can add the weight of a gearbox, and still come out ahead.

For instance, the weight of the Multiplex BL-480 4G (including 4.4:1 planetary gearbox) is listed as 117 grams. The weight of the Himax 3516-1130 is listed as 134 grams, i.e. the outrunner is 17 grams heavier.
Take a look at these two links:
http://www.hobbyhorse.com/himax.shtml
http://www.multiplexusa.com/motors/B...rive/4Gear.htm

Then again, the Hacker is listed at 3.7 oz (105 grams), so it is lighter yet. If the lower maximum current rating isn't an issue, it may turn out to be a very good alternative motor option. Too bad the Kv isn't a couple hundred rpm/volt lower, that would have made it even better.
Quote:
Originally Posted by Jeremy Z
Also, you lose efficiency in the gearbox.
True, but how much? I've been told that 3% is a representative number. That's not very significant.
Quote:
Originally Posted by Jeremy Z
If it were as simple as you make it sound, the designers would've thought of it.
They have - why else have we been using geared electric motors to fly our model airplanes for years?

Now that we have lots of (relatively) inexpensive outrunners, there is a viable alternative to gearing. Each one has pros and cons - the outrunners have simplicity, cost, and quiet on their side, the inrunners generally have higher efficiency, but cost more and have some gearbox noise. In the case of the AM, there's also the fact that several outrunners will bolt in, and chances are some slight mods will be necessary for any geared inrunner option.
Quote:
Originally Posted by Jeremy Z
I have to admit, I'm curious to see if you're going to put your money where your mouth is with regards to the power system, or leave it as a theory.
You make it sound as if I'm suggesting that only geared motors are a worthwhile option. Not at all. As I've said several times, there are pros and cons to both outrunners and geared motors. Quite obviously, everyone is free to buy and use whatever they think is best. And I haven't decided which way I'm going, myself. Do I want to shell out some extra bucks and have perhaps have to modify the motor mount to gain the benefit of increased efficiency and thrust? Or do I go for convenience and just bolt in an outrunner?

I can tell you that I've more or less narrowed it down to one of three choices: the Hacker A30-16M, the factory recommended Himax 3516-1130, or the Multiplex BL-480-4G. The Medusa option looks very promising, but I'm not willing to pay the extra cost ($50 for the gearbox alone), so it's out of the running. Similarly, the Power 10 is less efficient than any of the others, so it too is out of the running. (Nothing personal, Jeremy, so please don't think this is any kind of dig at you. My decision is purely based on the similar price and reduced efficiency of the E-flite versus the other outrunner motors).

There's absolutely no reason for the "only one opinion can be right, and everyone else is wrong" mindset. The whole point of a public forum like this is the sharing of ideas and opinions - the value is in the differences of opinion as much as it is in any shared agreements!

It's weird, on most build threads on RC Groups, many people enjoy discussing alternatives. After all, the factory cannot optimise everything to suit everyone's taste, and everyone's wallet, so there's plenty of room for alterations to suit personal taste. But for some reason, on Multiplex threads, there is very little of this. Rather, some react with shock and horror at any suggestion other than following the factory manual. It's a bit like the folks who build PC's (the more mods the merrier) and the folks who love Mac's (Apple is sacred, and any mod would be sacrilege).

I feel a bit like a PC guy who wandered into a Mac forum. And none of the attitudinal differences makes any sense to me, because in the end PC's and Mac's are not very different at all - most of the hardware has been shared for years, from video cards to hard drives to memory, and nowadays with the Intel Mac's, there are virtually no significant hardware differences at all.

-Flieslikeabeagle
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