Started by isoaritfirst, March 16, 2009, 10:09:18 am
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Quote from: mr ed on March 16, 2009, 11:25:40 amExcellent, thanks again. This needs a sticky.
Quote from: isoaritfirst on March 16, 2009, 10:09:18 amVisit;Picasa Web Albums - mike - RCRCM SigmaThe text and pictures within this Sigma build detail the installation technique. With a few detail changes as I was building two sets of wings each to have identical installs - It has worked so well that neither wing requires any sub trim over the other. This Text and pictures are based around my FS3 flap servo install. (x- over installation using flap offset mix)The servo will be fitted onto the top skin of the wing with the arm facing downwards, and servo shaft closer to the wing spar than the TE. The pushrod will cross bottom to top exiting through the top skin to meet the top mounted flap horn. The transmitter will be programmed to give a flap offset mix. (IMPORTANT - don't use this technique if you are unable to offset the servo centre position. approx 25deg/95deg.)Calculate the lgth of push rod needed. It can be a best guess a few mm either way won't matter, and make up the rods so that a clevis is soldered to the servo end and short threads are left at the opposite end for the flap surface clevis.On the bench; Plug the two servos into a receiver and move them both to maximum deflection in opposite directions. (Use a clean aileron input into each).Switch off the receiver to freeze the servo at that position. Useing the shortest servo arm available (usually around 7 to 8mm ctrs). Fit the servo arms so that each of them is positioned at the maximum rearward position. This will be when the servo arm is pointing directly at the hole in the flap horn. Experiment with different arms until you find two that give very similar locations on their splines. With Futaba 2,4 or 6 splined arms each have a slightly different angle from the centre so its important to get a matched pair. Switch on the servo power again and check their alignment.Fit the two push rods onto the servo arms, and using the transmitter move both servo to their maximum opposite direction and switch off. With the servos sitting head to head on the bench the clevises will now be fouling the servo centre shaft and forcing the rods to be pointing 45deg up away from the bench. Grind the clevis keeper and also clean up the servo arm to allow the rods to almost touch the bench at the point where they start to foul. Make them both identical. Remember that when the flap clevis is attached they will be longer. You may not be able to achieve full forward deflection of the servo, you will need to make a judgement call as to how much you are prepared to remove from the clevis, to how much loss of rotation you can afford. You should be able to get somewhere around 110 deg total without too much trouble. With the servo arm as far forward as possible,(transmitter driven) trial fit the servo into the wing. Screw on the second clevis and attach to the flap. With the servo arm at its furthest forward rotation and everything connected up hold the flap surface deflected by the maximum amount of up (aileron) you require. Now adjust the rod length to position the servo appropriately in the wing pocket. Don't be greedy with the amount of up flap 5mm up at the root is about right. When happy manually force the servo arm around slightly until the flap surface is level. Remove everything and solder the flap clevis onto the rod at that position. Make the second rod EXACTLYthe same length and solder together.Position the second servo's rotation point by using the transmitter, to approx match the one just removed. Take a reading off the transmitter as to its position. Set the first one, using the transmitter to the same position. This will be the rotation point where the surface is level. Aim for them both to be identical.Now connect everything up, with the servo powered at the position that gives a straight flap surface. Make a transmitter output channel that has the appropriate offset so that the servo will stay put, it will be around 75% deflection (Keep the servo powered up while you do this. ) add some glue to the servo pocket and then tape the flap surface straight and check that the pushrod runs perpendicullar to the surface hinge and runs through any exit holes cleanly. Now simply allow the servo to find its natural position in the wing and squeeze it into the glue bed. I hold the servos in position while they dry by placing my lead melting pot onto the servo. The addition of a small piece of blue foam sitting on the servo creates a raised area for the pot to sit on.Don't use much weight - just enough to keep everything still, you don't want to deform your skins. Use 30minute epoxy and microballoons. When everything is dry and the servo is switched on to a clean channel it will centre with the flap surface probably deflected down by around 30deg . You now need to apply a flap offset into the program to bring the surface back to level.Standard servo rotation is 120 deg (+- 60deg) Usable rotation with a crossover installation is probably closer to 110 deg. But by using flap offset this can be set in the region of +20 -90deg.NOTES;With most modern mouldies the surface horns are predetermined and fixed so no adjustment is available here. (another subject)The amount of down going flap will be the maximum achievable with a short servo arm (mounted inside the wing skin) More flap can be added at the expense of up flap(aileron). So when deciding how much up flap you need - do not be greedy - take a realistic approach.If you do want more of everything then you will need longer servo arms, which bring their own problems. (yet another subject)The install is not geometrically perfect for minimum slop at level, the servo position is not perfect for that but gives advantages at other points of deflection. (and another )At maximum deflection the servo arm will be directly in line with the push rod - which will save the servo gears if you are prone to landing flap down. It also gives the servo maximum torque at the point where it is needed most.
Quote from: isoaritfirst on August 05, 2009, 22:48:25 pmAny channel will do - just make sure its a fresh- clean signal. you dont want any mixes or sub trims etc, just a full 120degrees of clean input and a centre that is true.
Quote from: Lee Morgan on November 22, 2010, 18:43:19 pmRight last attempt at putting across what I meanWhen the flaps are down . putting in left or right ail would also bring the up going flap all the way up . so one would be all the way down and the other all the way up , this means steering whilst the flaps are down would be extreme to say the least .
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