SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Sep 18, 2012, 04:44 PM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
2,877 Posts
This is looking good. I'd think that this layout could be durable enough for a 3m wing, although I bet that the motor ends up in front of the mechanism to make the CG happy.....we'll see.

Keep going Stuart !

Kent
Knoll53 is offline Find More Posts by Knoll53
RCG Plus Member
Latest blog entry: Sw-11
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 18, 2012, 05:15 PM
Just call me crash for short
Quick61's Avatar
United States, OH, The Plains
Joined Jan 2011
1,697 Posts
Good thinking Stuart, having the drive pull the wings out instead of pushing. Your drawings are looking good too. One of these days were going to have to get you into a CAD program of some kind.

I sat down for a few moments this afternoon and pecked out a piece of code for the receiver interface. I'm hoping that I am at least close on this as at the moment I do not have any simulator software or a circuit to test it out on. For now, all I can do is put up the code and maybe someone that has experience with the Ardunio IDE and programming the Atmel ATtiny chips can tell how correct or wrong it might be. On the bright side, at least it compiles with no errors.

Mark

Code:
/* 
Program to sense PWM from R/C receiver and drive a transistor
H-Bridge for reversing a DC motor.
*/

int duration;

//Set pwm read and output pins

int pwmpin = 3;
int outA = 5;
int outB = 6;

void setup()
{
  //Set input and output pins
  
  pinMode(pwmpin, INPUT);
  pinMode(outA, OUTPUT);
  pinMode(outB, OUTPUT);
}

//begin reading pwm and seting pinstates

void loop()
{
  duration = pulseIn(pwmpin, HIGH); //Pin 3 reads receiver pulse freq
  digitalWrite(outA, LOW); //Normal state pin 5 = off
  digitalWrite(outB, LOW); //Normal state pin 6 = off
  {
  if (duration > 1201) //Motor fwd if rec pwm lower than 20%
  {
    digitalWrite(outA, HIGH);
    digitalWrite(outB, LOW);
  }
  if (duration < 1799) //Motor rev if rec pwm higher than 80%
  {
    digitalWrite(outA, LOW);
    digitalWrite(outB,HIGH);
  }
  }
}
Quick61 is offline Find More Posts by Quick61
Reply With Quote
Old Sep 19, 2012, 01:59 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,380 Posts
Quote:
Originally Posted by Knoll53 View Post
This is looking good. I'd think that this layout could be durable enough for a 3m wing, although I bet that the motor ends up in front of the mechanism to make the CG happy.....we'll see.

Keep going Stuart !

Kent
Thanks Kent.3mThis thing keeps growing.
Re the motor thing,I hope it's going to be ok where it is.The weight is about 40g.What prompted me to place it here were Herks comments in #311,and the push/pull advantage.
Still a lot to do before anything leaves the drawing board!
Regards Stuart
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old Sep 19, 2012, 02:27 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,380 Posts
Mark,I can in no way make any comment on the code thing.Maybe the DIY electronics guys could give some useful feedback?Though from what I've seen I doubt you need it!
I'm afraid I'm stuck with paper and pencil for now(I could do with borrowing Kents drawing board)
On the motor,the motionco. GMP16D4 4:1; 350rpm@3v mentioned in #233 looks as though it will be fast enough.If you think it will be mechanically/electrically ok I'll put it on the shopping list.

regards Stuart.
Stupot46 is offline Find More Posts by Stupot46
Last edited by Stupot46; Sep 19, 2012 at 02:46 AM. Reason: Addition
Reply With Quote
Old Sep 19, 2012, 03:55 AM
Just call me crash for short
Quick61's Avatar
United States, OH, The Plains
Joined Jan 2011
1,697 Posts
Quote:
Originally Posted by Stupot46 View Post
Mark,I can in no way make any comment on the code thing.Maybe the DIY electronics guys could give some useful feedback?Though from what I've seen I doubt you need it!
I'm afraid I'm stuck with paper and pencil for now(I could do with borrowing Kents drawing board)
On the motor,the motionco. GMP16D4 4:1; 350rpm@3v mentioned in #233 looks as though it will be fast enough.If you think it will be mechanically/electrically ok I'll put it on the shopping list.

regards Stuart.
That's shiny, i really wasn't expecting you to go over every line, just maybe someone sees it that might know something more than I. I think I have already found a way to do it better (and what I have might not work at all the way it is) so I'll keep trying to refine it and have it ready for when the parts show up. At least I'll be able to make a good running start.

That motors the one i was basing the parts for the H bridge on. The common switching transistors can handle ~500ma+ each and with the motor is only ratted at pulling 70ma at max efficiency which leaves us with over 400% margin for error. They should work well flowing the "juice to the moose". That RPM goes up to 1800 @ 12v so it will all depend on how much battery you drop in the ship. Anything more than a 2S LiPo and you will need a BEC for sure, (for receiver and motor control logic), but a 3S would make that motor move and give you some weight to shift around at the same time - 2 birds, one stone kind of deal...

Mark
Quick61 is offline Find More Posts by Quick61
Reply With Quote
Old Sep 19, 2012, 04:59 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,380 Posts
Thanks Mark,that's on the list.
To avoid any end force on the motor drive shaft I've ordered a small thrust race to fit between the coupling and the rear pillow block.This will take the pressure as the wings are opening(I think I've got that the right way round-the shaft will try to move forward as it drives the nut back- sounds ok) To the same end I think the coupling I mooted earlier would also be a good idea to isolate the motor from end forces.
Regards Stuart
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old Sep 19, 2012, 08:41 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,380 Posts
An idea for the mechanically minded.Bought some A1paper this morning,and while starting to redraw,noticed a way to possibly simplify the linkage.
If the ball connecter on the drive nut was fitted with a piece of 3mm music wire,and this in turn slid into a suitable tube in the wing root,would this be strong enough?The maximum length of wire from nut to disc edge would be 20mm,maximum total length approx 80mm.Seems a decent idea,opinions and critisms on a post card to the usual address please
Stuart
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old Sep 19, 2012, 05:53 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,380 Posts
A sketch to illustrate.I've sourced some all metal ball links,so the question is would music wire or a suitable alternative be up to the job.
Advantages are-fewer parts and links,and the drive could be more compact;without the length of the arms the motor can move forward at least 70mm.
Stuart
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old Sep 19, 2012, 07:31 PM
Herk
HerkS's Avatar
Virginia USA
Joined Jun 2007
1,652 Posts
Hi Stuart - that looks workable.

You have three different loads to deal with.

1. flight loads - suspect that these will be relatively negligible.

2 Friction loads - depend upon the design of your rotational support system.

3. Landing loads - I think these will be the big ones. You will probably want to land with the wings fairly forward, so mechanical advantage should probably be biased toward that configuration.
HerkS is offline Find More Posts by HerkS
Reply With Quote
Old Sep 20, 2012, 04:24 AM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,380 Posts
Thanks Herks,succinct analysis.
The first two points can be covered by a bench test rig.
The third-(inserting"bad" before landing)needs a bit of thought.Could the springiness of the wire work to advantage?Maybe a shear pin arrangement on the drive fixing.
Regards Stuart.
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old Sep 20, 2012, 11:35 AM
less is more
Knoll53's Avatar
United States, CA, Marina
Joined Sep 2006
2,877 Posts
Quote:
Originally Posted by Stupot46 View Post
If the ball connecter on the drive nut was fitted with a piece of 3mm music wire,and this in turn slid into a suitable tube in the wing root,would this be strong enough?
Stuart
I gotta hand it to you Stuart. You are more willing than most to explore new ideas in the forum. Not every body "gets" how well this works.

Here are a few observations to ponder....

Being a pilot who flies at the beach, I see some problems with the music wire sliding in the sleeve design. In a word. Sand. The binding and drag that debris in the slide would create could be unnoticeable, but still cause extra load on the servo and high battery use. Also, there will be "some" slop in the wire / sleeve interface. As the wire gets withdrawn, the slop increases.

Also the load on the music wire will be in bending rather than an axial load, which is not good. A hard landing may bend the music wire.

The previous direct linkage with ball links has none of these issues.

Kent
Knoll53 is offline Find More Posts by Knoll53
RCG Plus Member
Latest blog entry: Sw-11
Reply With Quote
Old Sep 20, 2012, 12:07 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,380 Posts
Thanks for the kind remarks Kent.As you say,the inevitable dust and dirt could be a problem,but I still have it in mind to make the wings detachable at the pivot;the wire would then just slide out of the tube.Thanks for pointing out the slop issue,hopefully that and the flex will show itself on bench.
The first two wing roots I make will be purely for testing.If I leave a 200mm stub "wing" on each one that will enable me to stand the whole thing on blocks and see how it
performs under load.I'll also build in fittings for both systems.
Regards Stuart
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old Sep 20, 2012, 12:22 PM
Closed Account
Joined Jul 2009
745 Posts
Stuart (our intrepid little inventor )

First off these ideas of yours are very inspiring. I have been sitting here just reading along as somehow i just cannot find any free time to actually work on anything other than the the wife's list of stuff I "need" to do. But nonetheless yardwork is giving me time to mull over your ideas and the input from everyone else. Although I do have a concept for something like this in my head, lacking time I still have not brought it anything near all the effort you have already done.

But let me just say great work Stuart and keep it up. Really fascinating stuff.

Jens
kleinaberfein is offline Find More Posts by kleinaberfein
Last edited by kleinaberfein; Sep 20, 2012 at 12:26 PM. Reason: Help I cannot type!!
Reply With Quote
Old Sep 20, 2012, 12:23 PM
I don't like your altitude
Stupot46's Avatar
Joined Sep 2011
3,380 Posts
First few bits arrived.The small thrust race for the drive shaft,the bushes and alu channel above and below the drive nut.The bushes were considerably cheaper than a length of equivalent brass tube.
Stuart
Stupot46 is offline Find More Posts by Stupot46
Reply With Quote
Old Sep 20, 2012, 12:37 PM
Just call me crash for short
Quick61's Avatar
United States, OH, The Plains
Joined Jan 2011
1,697 Posts
re - post #356 above

I'd be real inclined to go with Kent on this one. Not much speaks louder than experience. Sense were worried most about "shock load" and the ability for the rods to withstand and remain true, I'd suggest using carbon fiber rod. It will pull as much if not more than wire will and any bending that would happen during a 'sudden stop' would spring right back. Sense their pulling open anyway, any extreme push load would occur in something like a ground loop or the like. If you were to go with a sliding rod, something like the way these spoilers are set up would be better than a full length tube as they would be more apt to be self cleaning. Still, I think a rod between 2 fixed points is the simplest and best way to go.

Just thinking out loud...

Mark
Quick61 is offline Find More Posts by Quick61
Last edited by Quick61; Sep 20, 2012 at 12:40 PM. Reason: re - post #356 above
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Best electric plane in 16 mph wind? Sailor03 Electric Plane Talk 42 Nov 23, 2012 03:40 PM
Discussion Why do airplanes take off in to the wind? - news article jduvall Electric Plane Talk 65 Jun 15, 2012 08:29 AM
Discussion Make Sure Your Wind Turbine Is In The Wind Big Foot 48 Life, The Universe, and Politics 0 Apr 04, 2012 10:22 AM
Help! DJI Naza wind issue!!!! (help needed with throttle up issue in wind) Arxangel Multirotor Talk 11 Mar 07, 2012 02:47 AM
Sold ~closed~ WINDSHEAR II Aircraft - Fuel - Engines and Accessories (FS/W) 2 Oct 14, 2011 12:15 AM