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Old Jan 26, 2011, 06:39 PM
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USA, NC, Matthews
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Jepe Fast Foam Mirage 8s/glassed/retracts

I am still waiting on the kit to arrive but have made a good bit of progress with the power system and retracts so I am going to go ahead and start a build thread.

Equipment used:
Arc 36-75-1 motor
Midifan Pro
Hobbywing Pentium 100amp HV Opto ESC
8s (4sx2) 4000mah lipos, will try GForce or the new Turnigy Nanotech
CC BEC
Electric retracts, Freewing for nose and Changesun for mains with gear doors.
Futaba FASST radio

Will be glassed with WBPU and 25g fiberglass.

This is my 4th Mirage. One was "glassed" with just WBPU, one with finishing resin and one just painted so glassing this with actual fiberglass will be a first for me.

Will have rudder and I am adding a CF spar. Even though the spar isn't supposed to be needed, I have seen 2 wing failures on these, both with retracts installed so I am not taking any chances.

I have an old airframe that I am using to mock up the retracts etc. The test gear doors are plexiglass but I will be making the final ones out of aluminum. This should make it easier to bend/form them to match the bottom of the find with no gap.

I really hated the way the front gear steering was designed. I didn't want to go with a pull/pull setup either so I designed this one. The nose gear stays centered by a rubber O ring applying turning resistance. Also, the gear door is servo driven and I mixed a delay in the radio for the gear door channel.

Here are a couple videos showing their operation.

Front retract test (0 min 12 sec)


FILE0007 (0 min 20 sec)
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Old Jan 26, 2011, 07:12 PM
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Robert Belluomini's Avatar
United States, KY, Crestview Hills
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Looks good. How heavy are the Tamjets struts.
How about some additional details on your steering actuator, great Idea.
Did you simply form the fork from aluminum and then thread a long ball end to the strut?
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Old Jan 26, 2011, 07:19 PM
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Looks good man!
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Old Jan 26, 2011, 08:14 PM
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USA, NC, Matthews
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Thanks. Struts and wheels weigh 120gr. Here are a couple more shots of the steering link. Should be self explanatory.
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Old Jan 26, 2011, 09:32 PM
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Charlotte, NC
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Metal gear servo? I would think it would need to be.

Do you think adding a pocket of some type on the aluminum piece to accept the ball would help to reduce slop and provide cushioning? Maybe just a blob of silicon on the arm part, put some oil on the ball and let the silicon set up with the ball in it. Then the ball would come out easily but it would have a little flexible pocket to sit in.

you know I have to add my .02 cents
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Old Jan 26, 2011, 09:44 PM
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Nope that servo is not metal gear. I will replace it with one if there is an issue. No slop to speak of with the way it is. The sides of the metal bracket are pinched in so it is just touching the ball on both sides. Can't use a pocket as the contact point of the ball and bracket moves up and down a bit as it moves back and forth. I suppose I could make the bracket out of a pliable plastic with maybe a rubber band around it to provide some shock resistance. Hopefully that isn't needed. This setup shouldn't transfer any more stress to the servo as a normal pull/pull or slip joint steering setup. Time will tell though.

Actually just tested putting some stress/twist on the strut with the servo unpowered, Seems it translates to a side to side flex on the servo horn as opposed to torque on the servo rotation axis. Should be fine.
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Old Jan 26, 2011, 09:47 PM
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Cool idea, looks like a nice easy install!
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Old Jan 27, 2011, 06:27 AM
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Did you sleeve the 4mm hole in the strut? I'll assume these are 3.5 mm wire legs in the retracts?
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Old Jan 27, 2011, 06:36 AM
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I sleeved the mains with brass tubing and its a perfect fit. The nose is already a 4mm pin stock.

I do have some reservations about these retracts. Both sets were purchased for a different project. The Changesuns were purchased first but seemed a little on the small side. They actually have a metal trunion and may work just fine. I have had one of the 3 fail on me however. It just stopped responding. I opened it up and couldn't find anything obvious. The Freewings seem a little more robust but have plastic trunions. I broke one trunion, totally my fault, so that left me 2 good Freewings. Then the one I initially had for the nose stopped working. So, if any of these stop working, I will probably go with a more expensive, RCLander or similar set. One thing I do like about the Changesuns is that they will not activate if your gear switch is in the wrong position when you power up. They stay in the last position until you cycle the switch once. The Freewings don't do that.
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Old Feb 02, 2011, 08:43 PM
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Can you measure your Tamjets struts mains? The Flyfly wheels are about 2 1/4" in diameter. What is the distance from the bottom of the wheel to the top of the strut? What is the diameter of the strut? Does the strut attach to the retract using a wire insert?

Thanks.

Kelvin
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Old Feb 02, 2011, 10:13 PM
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Here is a pict that shows the size. They use a 4mm pin to mount to the retract. The struts are approx 11mm in diameter.
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Old Feb 22, 2011, 01:01 PM
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I built a FlyFly Mirage Jepe stye with a 36-75-1. The ARC motor is 12.5 oz and with your heatsink it will be heavier. Your batteries are only 30oz. I was using Rhino 4900 7s ( 3s + 4s packs). The weight of those 2 packs was about 32oz. I had to stagger the heavier pack forward towards the novse over the the lower pack to get it to balance according to Jepe's CG. Try to keep the nose section clear all the way to the forward part of the canopy just in case you need more weight forward and you can move the batteries.

Is your ESC rated enough? You'll be drawing more than 100amps with 8s on the 36-75-1. I was about 90 with 7s.

Kelivn
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Last edited by kelvin; Feb 22, 2011 at 01:07 PM.
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Old Feb 22, 2011, 01:07 PM
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Thanks for the info Kelvin. I was wondering about the CG issues. I made sure I could mount the batteries all the forward without the nose gear interfering so hopefully that will allow enough adjustment. I just installed some carbon flat bar to beef up the nose/retract area so hopefully with that and the plywood retract mount, it will be strong enough to allow the battery way forward.

By the way, you used air retract correct? Where did you have most of that gear mounted?
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Old Feb 22, 2011, 01:41 PM
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http://www.youtube.com/watch?v=XxxvxHkECx0

http://www.rccanada.ca/rccforum/showthread.php?t=115880

The wing will likely need a carry through spar (or two) glued in to hold your wings together. The youtube is from a plane with similar power on its last flight. The thread is from the same aircraft showing it's construction.
Cheers
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