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Old Jan 07, 2013, 03:06 AM
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Derby, UK
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Originally Posted by stevespana View Post
Hi to all Acromaster flyers.

So, motor would be Emax GT2812/10, 970kv, 105g, 12x6 prop, 320w
Esc:40A constant 50A burst, Servos as recommended by Mpx.

I am not looking for 3D flight, my aim is to develop smooth, precise, graceful acro's which I can then transfer to my bigger models.
Steve.
Hey Steve, the AM should suit you well - it is very robust and repairable, many have commented on its confidence-inspiring make-up. There are one or two faults which you can find in here - the u/c is cr*p, the nose can allow vibration and, personally, I find it flicky when trying to prop hang (probably my lack of skill).
If you keep the control movements low - 10-15 degrees each way, it will be smooth and steady. Your equipment looks fine to me - I wuold have said the motor was a bit soft but the other commenters use similar. I use a S1 Scorpion 3020 (sorry can't remember which wind) and a 12x6 prop. Throttle rarely goes above half - because it is flies slow enough to see what's happening and still carries through a manouevre. Your motor also looks a bit light for obtaining good CoG - your battery is likely to be far down the ramp. If there's a problem, get a 2650 or 3300mAh 3S, the AM will carry it's weight and I always have to land before I want to .
My AM is many years old and scruffy as hell. The fuse is bent and the nose is all bashed. The u/c went west a long time since (plastic finally cracked on a very cold day), but it only ever caught on our rough grass and bounced the plane over anyway, so no loss there. I've completely snapped it twice - full speed inverted or wing-tip landings do it for me . But it's still the plane I take to the field every weekend.

let us know how you get on
Nigel
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Old Jan 07, 2013, 10:43 AM
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Huesca, Spain
Joined Aug 2009
509 Posts
Thanks for the reply Nigel,

I think I've read through this entire thread twice and I'm pretty familiar with the pros and cons of the model. As I mentioned in my previous post I think the AM could be perfect for my needs. And the fact that it can be loaded into the car fully rigged for those "grab and go" flights is another plus factor.

If I do go ahead with the AM I will do a few mods to the notorious weak front end which will add a few of the missing grams of my proposed motor. I do also have some 2650mah lipos so all should be well.

I am aware that my motor may not be brimming with power but I think it will be sufficient for my needs. It hauls my FC around well enough and my observations are; that the weight, wing area and loading of the two models are very similar. As a point of reference, my Shark is flying on about 300W and weighs in at 1.7kg.

Cheers,

Steve.
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Old Jan 11, 2013, 05:34 AM
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Australia, NSW, Braidwood
Joined Nov 2008
790 Posts
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Originally Posted by stevespana View Post
Thanks for the reply Nigel,

If I do go ahead with the AM I will do a few mods to the notorious weak front end .............
Steve.
IMHO the front end is not weak, the motor mount is a poor design and this is what causes vibration problems.
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Old Jan 12, 2013, 08:44 AM
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Derby, UK
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Originally Posted by Watdazit View Post
IMHO the front end is not weak, the motor mount is a poor design and this is what causes vibration problems.
Well, being pedantic, a static part of a design can't cause vibration, the excitation must come from an alternating force, eg a rotating out of balance motor/prop/spinner, but incorrect adjustment of the mount might allow the force to produce a greater movement which, assuming the noise is the airframe resonating, will cause a louder niose, which is what we're all worried about, rather than the vibration per se, so I agree it can be part of the problem.

Equally, the nose is visibly a weak design - the relatively strong front is joined to the very strong wing area by an inadequate hoop or cylinder of EPP which is only two beads thick, reinforced by pillars of thicker EPP (just to the rear of the mount plastic reinforcements iirc). Usually a more than adequate design approach providing the hoop is strong enough to transmit loads. My view is the EPP is too flexible in this application. The modeller's reinforcement bridges the weakness to join the nose with the rest of the airframe, either via a wooden frame, or carbon rods fore and aft or thicker pieces of EPP glued into the thin areas.

Incidentally, reinforcing the nose moves the resonant frequency up in pitch, away from the exciting frequency range, but doesn't fix the cause, only the effect, (ie it doesn't stop your motor/prop/spinner being out of balance.) The thicker pieces of EPP probably work by damping the vibrations, without changing the pitch as much as the ply/carbon solutions. Choose your poison, as they say.

hope that helps
Nigel
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Old Jan 12, 2013, 12:39 PM
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Huesca, Spain
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Whoopee doo!

My FC is sold, and I now have the AM. I have to say that I'm very impressed with the precision and fit of the mouldings which, in my opinion, is better than the Minimag and Fun Cub.

Wow, the control surfaces are b----- big ! I've not started the build as yet, just browsed the manual and familiarised myself with the respective pieces.

The weather forecast for tomorrow isn't promising, so I guess I'ts a good excuse to begin the build.

Her indoors permitting of course.

Steve.
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Old Jan 12, 2013, 01:41 PM
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Australia, NSW, Braidwood
Joined Nov 2008
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Quote:
Originally Posted by Daddymonkey View Post
Well, being pedantic, a static part of a design can't cause vibration................
Nigel
The point of the motor mount being poorly designed in that it has on two points of fixing and under load it can rotate about the line of those two points and therefore the motor mount is not static. The only things which prevent this rotation are the bolts which adjust the thrust angle. If they are not jammed up hard against the side plates the motor mount will vibrate. I have an AM and a Funcub and they both suffer with the same design fault. My AM now has six fixings. I drilled and tapped the side mount so the thrust adjusting bolts are now part of the fixing and I use washers to obtain the thrust angle.

About the test of your discussion I do not know.
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Old Jan 12, 2013, 02:15 PM
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Hacienda Heights, Ca., USA
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The mount is more than ok. I enforced the nose of my AM very little and used a motor close to the specs that Multiplex recommends. If you over power your AM and plan on flying it like a racer, you'll likely have nose problems. It cuts through the sky very well with a stock set up. The first AM I built had heavy reenforcement to the nose and a large powerful motor. The motor finally pulled the nose off during a snap. Keep it lite and simple. It's a plane that will last a long time. Nick.
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Old Jan 12, 2013, 09:55 PM
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Australia, NSW, Braidwood
Joined Nov 2008
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I use a stock setup. The fact that Multiplex put an "addendum" in the box covering the fitting of the motor mount I think supports what I say. We will just have to beg to differ.
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Old Jan 13, 2013, 11:04 AM
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Derby, UK
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I confess I haven't seen the addendum but it's perhaps a good sign that MPX are responding to concerns expressed here as well (presumably) as elsewhere.

Personally, I consider the mount to be an elegant design but I agree it is perhaps more elaborate than robust. Happy to agree there's more than one way to skin a cat (allegedly).

I think that at the time the AM was launched, I remember there was something of a craze for installing as much power in a model as humanly possible - 250-300W/lb and up! Nick's caution is sound; certainly mine is unpleasant to fly at constant full throttle.

I'm interested to know if anyone has experimented with the aerodynamics? The harrier has bad wing rock - has anyone fitted toblerone's to the inboard l.e. to try to improve it, or anything else?
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Old Jan 14, 2013, 04:37 AM
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Huesca, Spain
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Started the build yesterday.

I normally build very slowly and this will be no exception. I have everything prepped for glue, did a dry fit, checked and double checked everything.

I've pre threaded the motor mounts and they will be glued in this afternoon and left to dry while I consider how best to reinforce the nose a little without going over the top.

Considering drilling and tapping the mounts as per Watdazit also.

Steve.
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Old Jan 14, 2013, 03:17 PM
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Australia, NSW, Braidwood
Joined Nov 2008
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Enjoy the build Steve. As I have said the only mod I did on this my second AM (I destroyed the first) was to drill and tap (using the bolts into the plastic) the motor mount supports. I used washers to the thickness given in the manual to get the thrust angle right. One other thing you might consider is to mount a satellite Rx inside the fuse at the rear during the build. You will only need a 5mm hole in the fuse opposite to it to see the light to ensure it has initiallized.
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Old Jan 15, 2013, 01:31 AM
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Knoxville, TN
Joined Apr 2008
920 Posts
Quote:
Originally Posted by stevespana View Post
So, motor would be Emax GT2812/10, 970kv, 105g, 12x6 prop, 320w
Esc:40A constant 50A burst, Servos as recommended by Mpx.

I am not looking for 3D flight, my aim is to develop smooth, precise, graceful acro's which I can then transfer to my bigger models.

Your thoughts warmly appreciated.

Steve.
I think that power setup sounds good to go. Also, I have a IMAC friend who flies his AcroMaster only as a pattern ship and loves it. I think he's disgusted when I fly mine 3D.
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Old Jan 15, 2013, 12:49 PM
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Huesca, Spain
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Build progressing slowly.

I have beefed up the walls of the nose cavity slightly using 50mm wide open weave fibreglass tape and well rubbed in Uhu Por. Bridged over and around the motor mount and all is firm and secure.

Tail feathers dry hinged and ready for gluing.

Kerbob; I will be flying my AM only as a pattern/general aerobatic ship too. 3D flying is way beyond my skill level. Occasionally however, I do enjoy flying my smaller EPP models at high alpha into a breeze for a bit of fun.

Steve.
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Old Jan 18, 2013, 04:13 PM
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Huesca, Spain
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A little more progress today

The fuselage is now fully glued up. Tail feather hinges all glued up too and tomorrow should see them attached to the fuselage. I'm also hoping to get the wings completed also.

Really taking my time with this one and enjoying it.

Steve.
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Old Jan 24, 2013, 02:45 PM
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Huesca, Spain
Joined Aug 2009
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Update

Almost completed the build.

Just need to set-up the servos and finish off some of the decoration. Then, all that remains will be to sort the CG.

With luck, if the bloomin awful weather over here breaks for the weekend, might even get to fly the maiden.

Here's hoping.

Steve.
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