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Post by Vanders on Sept 14, 2008 21:25:09 GMT 10
Working on my Stinger today, following instructions that stated to run the control rods from the servo to the horn on the elevon perpendicular to the LE which is at 90deg to the fuse, but the hinge line isn't parallel to the LE so basically the the control rods aren't at 90deg to the hinge line.
Now I find that when I've tested the servos they want to jump/twist their way out of the servo bay.
To overcome a messy fix I'm thinking I might just get the smallest ball joint rod end to replace the standard clevisis to take up any tortional/twisting movement, which means added weight behind the cg?
Shouldn't all control rods be at 90 deg to the hinge line when using std clevisis?
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Post by thevon on Sept 15, 2008 7:10:55 GMT 10
Mark are the servos glued in? If not, they'll always jump/ twist when actuated.
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Post by Pij on Sept 15, 2008 7:11:24 GMT 10
My thought is that, if there's a z-bend on one end or the other (probably at the servo in this case) then that acts rather like a ball-joint, and should be able to handle a fair bit of off-hinge angle. Even so, I've noticed on some of my models, a tendency to bend the control horn a little sideways, when the hinge-rod angle wasn't perpendicular. I haven't noticed the servos twisting around, except in very cheap models with incredibly flimsy servo trays. How are your servos mounted?
Oops, cross-posted, sorry Andrew. But yeah, are the servos secure enough?
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Post by Vanders on Sept 15, 2008 11:43:05 GMT 10
Ok I've gooped the servos in & will see this arvo how they go.
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Post by thevon on Sept 15, 2008 12:34:56 GMT 10
Yeah Mark when I was changing flap servos in the Fazer, I sat them in there to check the length of rods etc, and got a big fright when I moved the sticks slightly and they popped straight out of the mounts! Had to press them fairly firmly to get them to move the flap rather than pop out! There's a lot of rotational force at the spine, and something has to twist!
Mark maybe it's the instructions but I wouldn't use Goop - takes too long and hard to remove them if needed. I reckon hot melt glue is the way to go (I keep saying this, and no-one seems to agree with me but I'm holding out as the lone voice in the wilderness). Quick and easy and if you need to remove one you can heat up a blade and slide it round the servo and pull it out like a tooth. (I assume this is a foam filled wing???).
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Post by Vanders on Sept 15, 2008 13:56:47 GMT 10
Wing is yellow foam core ply sheeted, I've used hot melt before & had 1 servo come loose........maybe I didn't use enough hot melt?
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Post by thevon on Sept 15, 2008 15:21:36 GMT 10
It's a good idea to rub the servo case with fine sandpaper. I've only used hot glue with EPP and white foam. Not sure about yellow foam.
Probably the best way is to smear the servo hole with 5 min epoxy, then wrap the servo in plastic shopping bag plastic, push the servo in and let the epoxy set. Pull the servo and plastic out. Then do the hot melt glue thing.
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Post by skyboyken on Sept 15, 2008 19:36:21 GMT 10
FWIW I think that 'potting the servos as Thevon suggests, using 5 min epoxy and microballoons, is a great way to go. That's what a lot of fast foamy manufacturers recommend as an example.
Once the glue has dried you can just 'pop' the servo out and take off the glad wrap. It works really well. Don't however use hot glue or anything else when putting the servo back. If you do it won't fit properly. Don't ask me how I know (blush!).
All you need to do is tape or cover over the servo and it won't come out.
Go Great!
Ken.
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Post by Pij on Sept 20, 2008 19:46:05 GMT 10
I have read in some EPP glider instructions, a warning to make sure you use a LOW TEMP glue gun. Because of that warning, I haven't used hot-melt at all.
Do you guys have a low or dual temp gun, or have you used the high temp ones without problems?
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Post by thevon on Sept 21, 2008 9:51:46 GMT 10
Pij hot gluing is really easy and basic. No, both my guns have been single temp, and you control it by unplugging it when the glue's just right. My old one would get too hot and melt foam if I left it on but the new one doesn't seem to. You can test it on a bit of scrap EPP - get it nice and runny but not melting the scrap, then turn it off and use it. The gun/ glue retains the heat for quite a while. If you need to, switch it back on for a bit.
The biggest problem with my old cheap one was that the tip got really hot, so you could do a lot of damage if you touched the tip on the foam. But the new one (Bosch) has a tube tip which works excellently and it doesn't get hotter than the glue, so you can push the tip into slits and squirt glue in.
For EPP I just cut the servo holes accurately and only ever use hot glue. It's just so simple to do and easy to remove them I can't see the point in anything else.
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