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Old Nov 05, 2014, 11:04 PM
Where is the lift?
cptsnoopy's Avatar
USA, AZ, Phoenix
Joined Nov 2005
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New E-Maxa fuse, servos in the pod or rudder?

Planning on using MKS 6100's for rudder/elevator. Hacker A20-10XL/4.4x1 gearbox. X-70 ESC. 18/10 prop. Both 3s-850 70C and 4s-850 70C motor battery and likely a 2s-1450 Life/regulated for radio. This boom came with pushrods but I'm wondering if servos in the rudder might help prevent having to use weight near the rudder to get it balanced?

Charlie
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Old Nov 06, 2014, 04:40 AM
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Romania, Dolj, Craiova
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The servo wires have the weight in the same ballpark as pushrods, about 7-11 grams per meter, depends on model/make.
So you must be aware that the difference is servo weight mainly, and small gain from replacing pushrods with servo wires, especially becuase their weight is distributed along the boom.
2*10 grams servos in the tail will require about 80 grams in the nose to balance.
If you have good balance ATM without servos, with your selected pack and motor/prop/ESC, everything fitted in place, then better use servos in pod, imo.
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Old Nov 06, 2014, 09:51 AM
agnotology
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On my recent e-conversion of a Maxa, I used four wires from a good quality USB cable (two 28ga signal wires, two 24ga power wires). The wires were about half the weight of the pushrods I removed (13.7g outers, 9.4g inner, 23.1 total). I also removed the bellcrank (3g), and drive the stab directly.

I saved about 14g, so the added weight from two 9g MKS 6100 servos at the tail was quite small. The moment arm of the added servo weight is a bit further back though. It was enough to balance my low cost 134g gear motor and TP 850mAh 70C battery. It also gave me more room up front.

Kevin

Edit: There was also an overall weight reduction by removing the pushrods and bellcrank, and the direct drive of the surfaces is a bit more precise than long pushrods.
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Old Nov 06, 2014, 11:29 AM
Where is the lift?
cptsnoopy's Avatar
USA, AZ, Phoenix
Joined Nov 2005
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Thank you for the info Guys!
Kevin, are your rudder/elevator servos in the vertical install similar to the Supra?

Charlie
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Old Nov 06, 2014, 11:40 AM
agnotology
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I'm not sure what the Supra set-up looks like.

I just cut a round hole (25mm dia?) in one side of the fin back near the hinge line and just above the boom, basically where the elevator servo ends up. I removed the bellcrank and it's mount. I mounted the rudder servo forward in the fin upside down, with a slot for the arm. The elevator servo drives a short pushrod vertically, with a ball-link on the end that fits the aft stab rod. I put a spacer on one side of the stab rod to keep the ball-link centred. Two spacers would be better, but I haven't figured out an easy way to do that, and this has worked fine so far.

Both servos are just mounted with a thin layer of Goop. The rudder servo is bonded to the inside skin of the fin. I removed inside skin and foam locally where the elevator servo goes, so I could get the max length servo arm inside the fin. The elevator servo is bonded to the top of the boom and the CF at the hinge line of the fin.

Hope that is somewhat clear. I should have taken photos. I'll try to when I replace the elevator servo. I put a used one in there, and it started misbehaving this week.

Kevin
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Old Nov 06, 2014, 01:00 PM
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Joined Jul 2007
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The fin installations are different. I use Hyperion DS09AMD servos for all the tail installations (9 g, 27 oz-in torque). Supra e-fin has a hatch cover allowing the servos to install then hook up externally. Maxa e-fin requires the internal ball link to the stab bell crank. The pictures show my solution to both. For Supra the 1/64" ply plate carrying the mounting posts is glued to the inside of the fin with black CA. The straps and screws hold all secure. For Maxa the 1/64" base plate and posts are assembled, servos attached, then the whole unit slides into the fin and is secured with screws through the fin side to the mounting posts. The picture shows three screws, but I added a fourth (now two to rudder) after the rudder got sloppy and I discovered the one post that wasn't secured with a screw had come loose. Takes a bit of jockeying to get the unit in the fuse and bell crank attached, but it can be done in the field. The pix should be self-explanatory.

JT
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Old Nov 07, 2014, 07:16 AM
Where is the lift?
cptsnoopy's Avatar
USA, AZ, Phoenix
Joined Nov 2005
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Ooops! I should have been more specific, this is the newer Maxa fuselage with the pylon mounted horizontal stab/elevator setup. There is no bell-crank for a full flying stab. Vladimir has it setup for pushrods to the pod. I thought I'd read a thread here on the groups that mentioned someone needing to add weight to the tail after installing one or both servos in the wing pylon area.

Charlie
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Old Nov 07, 2014, 07:44 AM
Flying = Falling (Slowly)
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Tulsa, OK
Joined May 2004
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I've got two Maxa's, both older style. One has the servos mounted up front in the pod (pushrods) and one has the servos mounted in the fin.

With your motor and battery setup (850 3S) you should be able to get the plane to balance without any tail weight (the receiver pack may be a little problematic, though). You will want to arrange things so the battery can be installed as far back in the pod as possible. The problem I had with the front mounted servos was making room for ballast.

I would recommend that before you glue things up that you put everything together and see where your balance comes out. Then make up some mockups of your batteries, receiver and ballast to make sure that you will be able to take them in and out before you build the boat in the basement.

All in all, I like my Maxa with the front mounted servos much better than the tail mounted one. It is a little lighter unloaded -- which may or may not make a difference -- but keeping weight out of the tail allows it to handle substantially better.

Happy Landings,

Don
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Old Nov 07, 2014, 12:02 PM
agnotology
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Joined Jan 2007
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Sorry, I'd forgotten what the new fuse looks like.

I would definitely mount the servos forward as intended in that fuse. You might need a 100g motor to get the CG right. The Redfox motor is now available for a semi-reasonable price.

The inertia in the pitch and yaw axis has the r^2 term, so avoiding excess weight in the tail is important for handling as Don noted. A 10% difference in the pitch inertia wasn't worth the extra $300C to me at the time, and the old fuse is very crowded up front with the e-power equipment.

I've attached my Maxa (short tail) version of Dan's excellent weight and balance, and static margin spreadsheet. It is pretty easy to change the locations and masses of all the parts to see where the CG and static margin are going to come out. A 6 or 7% static margin should be about least trim drag at best L/D (a slight download on the tail).

http://www.rcgroups.com/forums/showthread.php?t=1106300

Kevin
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Old Nov 12, 2014, 11:47 AM
Where is the lift?
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USA, AZ, Phoenix
Joined Nov 2005
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I got the motor/ESC/propeller mounted yesterday. After playing around with different combinations I decided to mount both the rudder and elevator servos in the keel as far aft as I can. In my opinion it was the easiest option but not necessarily the best for avoiding having to add some weight to the tail. if it gets windy out, I'll just grab the supra.
Thank you all for your helpful input.

Charlie
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Old Nov 16, 2014, 02:03 PM
Where is the lift?
cptsnoopy's Avatar
USA, AZ, Phoenix
Joined Nov 2005
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As expected, I cannot get a CG aft of approximately 96mm when I try to use a 4S-850 along with a 2S- 950 receiver pack. Using a 3S-850 I was able stack the two batteries and push them both back to the servo tray. That got me to a more acceptable 102mm CG. I flew it that way in our monthly ALES contest yesterday and was very happy with how the e-Maxa performed.
While I was playing around with different component placement options, I found that there is room to fit two 2S-550 batteries behind the servo tray and I once I buy 2 new ones, I'll give that a try. That should open up the pod for a much broader range of motor batteries without moving the CG out of my desired range. Just food for thought.

Charlie
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Old Nov 19, 2014, 02:27 AM
Where is the lift?
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USA, AZ, Phoenix
Joined Nov 2005
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Here is the 2S-1100 mah battery that actually slides in behind the servo tray. The foam is a backstop to keep the battery from hanging on the wires during launch and the voltage regulator sits just in front of the battery preventing it from moving forward during landing. I am hoping that this will make a significant difference in motor battery options while maintaining the desired CG.

Charlie

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Old Nov 24, 2014, 01:52 PM
AZ Outback
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What is the weight of a Hacker A20-10XL/4.4x1 gearbox? Long boom or short? Large stab or small?
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Old Nov 24, 2014, 02:02 PM
Where is the lift?
cptsnoopy's Avatar
USA, AZ, Phoenix
Joined Nov 2005
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Hi Bobby,

I have to apologize, it's in the fuse and I did not weigh it.
Long boom, large stab
Rudder and stab covers both say "Light"
Just now playing with the CG after mounting the radio battery in the aft pod behind the servo tray. It's much better now. The 4S-850 is approx 4" further forward with a CG at 102mm. Now there is room for higher a mah battery if I think I need it.

Charlie
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Old Nov 24, 2014, 05:45 PM
AZ Outback
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Joined Dec 2000
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You will want cg around 109, I have two mks6100 in the pylon, and Vladamir has a new fuse that uses inverted ones in a wider pylon, so you can add ballast, which my mount does not allow for. I use a TP1300 pushed all the way to the pylon for balance. I would just tape everything in position inside or out and see what works. Good Luck with the build.
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