SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Aug 31, 2012, 11:34 AM
Registered User
United States, CA, Camarillo
Joined Jul 2012
387 Posts
Quote:
Originally Posted by Bugman Jeff View Post
I've been using MG90S servos everywhere but the rudder. I can't seem to find a stall current rating for them anywhere, but so far so good. Has anyone actually overloaded their BEC yet? If so, does it just shut down until it cools off?
Jeff,

Your analog MG90S servos are manufactured by Tower Pro in Taiwan.

http://www.towerpro.com.tw/index.asp

I looked for the stall current, but Tower Pro doesn't list it in thier specifications sheet...

http://www.towerpro.com.tw/driver/dr...rvo%20spec.pdf

You'd need to ask Tower Pro directly by e-mail or do your own stall testing. Otherwise, you would just to assume a conservative current value, like what TooSLow2Care does.

Barry
Barry2020 is offline Find More Posts by Barry2020
Reply With Quote
Sign up now
to remove ads between posts
Old Aug 31, 2012, 11:03 PM
Registered User
United States, CA, Camarillo
Joined Jul 2012
387 Posts
Horizontal Stabilizer Attachment Thumbscrews

I didn’t like the idea of needing a screwdriver every time the plane was assembled, so I replaced the two steel screws at the stabilizer with nylon thumbscrews.



I’m using nylon and brass standoffs to extend the female threads in the tail. The brass standoff is used as a solution for any nylon threads breaking off down inside the vertical stabilizer where they would be difficult to remove.

You can see that both of the nylon standoffs sit up above the flat mating surface of the tail. This allow for sufficient thread engagement of the thumbscrews.



I didn’t weigh the parts, but it doesn’t look like much weight savings.



The male threads of the nylon standoffs needed to be trimmed to allow full insertion into the brass standoff and provide the correct standoff height (30mm). I also used a hacksaw to cut a flat screwdriver slot in the top of the brass standoff; that allows for removing the brass standoff from deep inside the tail should it ever become detached from the nylon standoff.

The thumbscrews came with 16mm long threads, but to keep the thumbscrews from bottoming out in the standoff, I had to shave them down to 14mm long. All the nylon trimming was done with a box cutter.

All the parts were sourced from eBay to save time. I don’t think I would have been able to find the metric thumbscrews locally. Here’s the parts list and my costs in USD w/shipping.

- Nylon knurled head thumbscrews, M3-0.5 x 16mm, 100-pieces $10.00
- Nylon standoff spacer, M3 Male x M3 Female x 25mm high, 10-pieces $5.50
- Brass standoff spacer, M3 male x M3 female x 5mm high, 10-pieces $4.70
Barry2020 is offline Find More Posts by Barry2020
Reply With Quote
Old Sep 01, 2012, 11:14 AM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
I fly over corn fields, and more than once I've stalled it low and crashed into a field. After my last field rescue(do you have any idea how hard it is to carry a 8.5' sailplane through a 7' tall corn field? ), I decided I needed to add a lost model alarm. It's hooked into a spare Rx channel, and on a switch on my Tx. As long as I don't crash hard enough to eject the battery, it works pretty well, and doesn't disrupt airflow over the plane.
Bugman Jeff is offline Find More Posts by Bugman Jeff
Reply With Quote
Old Sep 01, 2012, 11:34 AM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
For curiosity's sake, I hooked up my amp meter inline with the battery, and stalled all my servos. I manually held all my control surfaces, and moved my Tx sticks(looked kinda like someone playing Twister ). I recorded about 0.8 amps with all me servos stalled. Even if my amp meter isn't the most accurate, it's still well within safe limits.
Bugman Jeff is offline Find More Posts by Bugman Jeff
Reply With Quote
Old Sep 01, 2012, 11:57 AM
Registered User
United States, CA, Camarillo
Joined Jul 2012
387 Posts
Quote:
Originally Posted by Bugman Jeff View Post
For curiosity's sake, I hooked up my amp meter inline with the battery, and stalled all my servos. I manually held all my control surfaces, and moved my Tx sticks(looked kinda like someone playing Twister ). I recorded about 0.8 amps with all me servos stalled. Even if my amp meter isn't the most accurate, it's still well within safe limits.
Jeff,

You'd need to measure the current in amps at the servo wires. What you measured was the current draw at the battery. The current would be much higher at the servos.

Assuming 100% effieciency of the BEC, 4S LiPo, and servo operating voltage of 5.25V, your servo current draw would be about 2.26 amps (0.800 amps x 14.8 volts / 5.25 volts ).

Your measured 0.800 amps seems low for "all" servos locked. Could be your BEC is not providing sufficient voltage to fully load the servos; which may explain why you only saw the 0.800 amps at the battery.

I like the field finder circuit. Thanks for showing.

Barry
Barry2020 is offline Find More Posts by Barry2020
Last edited by Barry2020; Sep 01, 2012 at 12:16 PM.
Reply With Quote
Old Sep 01, 2012, 12:16 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
Ah, gotcha. I see where my mistake is. To get an accurate reading, I should have the amp meter between the BEC and the Rx so I'm measuring the load directly at the Rx power input, right?
Bugman Jeff is offline Find More Posts by Bugman Jeff
Reply With Quote
Old Sep 01, 2012, 01:53 PM
Registered User
United States, CA, Camarillo
Joined Jul 2012
387 Posts
Quote:
Originally Posted by Bugman Jeff View Post
Ah, gotcha. I see where my mistake is. To get an accurate reading, I should have the amp meter between the BEC and the Rx so I'm measuring the load directly at the Rx power input, right?
Right. That would give you the total load of the BEC at the voltage the servos see.

It would also be useful to measure the voltage and current simultaneously. That way, you could see if your BEC can maintain the load requirements of all servos, Rx, etc. The servo stall currents for each manufacturer are given at a specified voltage( usually at 4.8V and 6.0V). You'd also want to test this with the battery near depleted or near the low voltage cutoff point, where a brownout situation would be more likely on a borderline system design.

After the high wattage resistors I ordered from China arrive, I'll be able to post the details on how I plan to test my ESC under a fixed current load. The Art-Tech 60A ESC that came with my D2500 has no stated specifications for the BEC. After I do the load testing, I'll know if it can handle the loads of the new digital servos I planning to purchase.

This whole exercise is just to avoid a Rx brownout, crash landing, and brush fire started from a crushed LiPo.
Barry2020 is offline Find More Posts by Barry2020
Reply With Quote
Old Sep 03, 2012, 10:41 AM
Registered User
United States, NC, Hendersonville
Joined May 2010
76 Posts
Hi BG,

I found this thread about a month ago, and have followed it with interest (I'm only up to #414). I had recently bought a D2500A and the recommendations you and others have suggested are most welcome. I did have a lot of difficulty getting the wings to fit in the Fuse as they were badly mismatched, but persevered and it had it's maiden flight last Friday. It flew like champ virtually flying out of my friend's hand at launch. It was stable even in some windy conditions. Had to add a few clicks of up elevator to trim. Also, I had mixed the flaps (which I added) with down elevator but, it was too much as the plane nose dived. I have decreased the down elevator and it should work much better the next time I fly it.

I set the CG as others and you recommended at 83.5mm and it is just a touch nose heavy with the 3S battery at the back of the cockpit. I want to get the 4S and 60 amp ESC later, but it will be too nose heavy. Removing the lead weights from the nose should take care of that issue. Can you tell me the weight of the lead in the nose?

I also cut the aluminum tube as you recommended to make the assembly easier and it worked very well.

Again, I appreciate the info from you and all the others, Thanks!
Jack McC is offline Find More Posts by Jack McC
Reply With Quote
Old Sep 03, 2012, 11:46 AM
Registered User
BG Bengtsson's Avatar
Sweden
Joined Jul 2010
186 Posts
Hi Jack
tanks for kind response to mine and others thoughts and writings. My D is now an old lady. I just a couple a weeks ago refurbished the wing mount. I added 1mm balsa cut outs on the fuse inside the body at wing fixing. Now it is tight again. I also think of glueing a thin plywood on the bottom side of the wing fixing pins. Especially the front pin has almost no foam for the pin to hold against.
The iron weight in the nose is 130g. Wing tip weight 2x25g.
Original al-pipe 837mm 128g Cut to 240mm 35gram. (But naturally even better to buy the Carbon pipe. I have unfortunately not done that yet.)
Taking away the nose weight and you shall have the 3S as far front as possible. And 4s as aft as possible. She is very unsensitive on CG. Just click some clicks when changing to 4s. If you feel it like pulling out of hand with 3S, just wait for 4S...!!! That is pulling out of hand.
I have two 3s 1350mAh 122g to go as low as possible for thermal. That makes CG maybe 85-90mm. Large 4S maybe CG 65-70mm.
Last saturday was the best day of this summer. No wind and blue sky and I had to just watch the day pass... Not funny at all.
/BG
BG Bengtsson is offline Find More Posts by BG Bengtsson
Reply With Quote
Old Sep 03, 2012, 07:04 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
I caught my first ever thermal today Right after I launched, I spotted a hawk in the area, so I flew over towards him. I flew around unpowered for about 20 minutes, and got higher up that I've ever had it. Of course, my camera cut out in the first 40 seconds of the flight so I don't know what the world looks like from that high up, but it's a start I seem to get the longest glides by powering up to altitude, then deploying full flaps.
Bugman Jeff is offline Find More Posts by Bugman Jeff
Reply With Quote
Old Sep 04, 2012, 05:58 AM
Registered User
BG Bengtsson's Avatar
Sweden
Joined Jul 2010
186 Posts
Hi Jeff
congratulation to nice soaring! I can feel your feeling! Its nice! Murphys law about the camera...
But what do you mean with ... then deploying full flaps. Did you really have full flaps while soaring?! Then it must have been real thermals, if you just could take the hang on the elevator! (maybe bad english... hope you anderstand)
/BG
BG Bengtsson is offline Find More Posts by BG Bengtsson
Reply With Quote
Old Sep 04, 2012, 10:58 AM
Registered User
United States, NC, Hendersonville
Joined May 2010
76 Posts
Quote:
Originally Posted by BG Bengtsson View Post
Hi Jack
tanks for kind response to mine and others thoughts and writings. My D is now an old lady. I just a couple a weeks ago refurbished the wing mount. I added 1mm balsa cut outs on the fuse inside the body at wing fixing. Now it is tight again. I also think of glueing a thin plywood on the bottom side of the wing fixing pins. Especially the front pin has almost no foam for the pin to hold against.
The iron weight in the nose is 130g. Wing tip weight 2x25g.
Original al-pipe 837mm 128g Cut to 240mm 35gram. (But naturally even better to buy the Carbon pipe. I have unfortunately not done that yet.)
Taking away the nose weight and you shall have the 3S as far front as possible. And 4s as aft as possible. She is very unsensitive on CG. Just click some clicks when changing to 4s. If you feel it like pulling out of hand with 3S, just wait for 4S...!!! That is pulling out of hand.
I have two 3s 1350mAh 122g to go as low as possible for thermal. That makes CG maybe 85-90mm. Large 4S maybe CG 65-70mm.
Last saturday was the best day of this summer. No wind and blue sky and I had to just watch the day pass... Not funny at all.
/BG
Hi BG,
That is the info I was looking for regarding the 3S and 4S without the lead weights in the nose. I had considered going with a separate nicd pack for the servos, but am reconsidering being concerned about the weight. If I remove the weights from the nose and find I need to add more I would then add the nicd rather than add lead weights. Less is better!

What I found most gratifying is that this is my first aileron/flaps plane and it flew better than I would have imagined. Stable and responsive, needing little rudder input.

Anytime you miss a good thermal day is never a good thing. Especially at the end of your summers. I am in the western part of North Carolina in the mountains, but we fly all year round. Used to live up north in the US and after Thanksgiving we would put the planes away until March of the next year. You learn to cherish those good days!

Thanks again for the info, it is much appreciated! Hope you get some good days before Winter.


Jack
Jack McC is offline Find More Posts by Jack McC
Reply With Quote
Old Sep 04, 2012, 01:51 PM
Registered User
United Kingdom, England, Taunton
Joined Sep 2011
31 Posts
Just crashed mine badly....

I gassed it coming out of a loop with full up elevator (due to approaching terra-firma) and hit a big tree at full throttle. It's a big old bird so it was moving at a fair rate. I think due to the size of the Diamond it was further away than i realized as i thought i had plenty of clearance between me and the tree.

Found the glider on the floor with the following damage:-

Fuselage snapped in half just behind canopy. Now gorilla glued back together.

Battery/rx tray snapped. Now fibre-glassed and gorilla glued back together.

Motor mount loose and cowling damaged. Had to hack the cowling off to fix the motor mount with, yes, more gorilla glue (and some ply..) Cowling glued back on. Motor tested and still runs straight.

Prop snapped both sides. Replaced with el cheapo version until it test flies properly

Right wing cosmetically damaged.

Left wing in shreds, the wing was separate from the glider when i found it with the following damage -
Wing joining tube at 30 degree angle instead of straight.
Wing snapped completely at root where the ply wing-mount terminates.
Wing snapped completely at wing-tip at end of aileron.
Both ailerons semi-detached.
Two big chunks missing and numerous dings in leading edge.

One of the two Rx antennas snapped.


Bizarrely, after all this, i still think it is fixable.
The fuselage (after fixing), right-wing and tail look good.

I've glued the missing chunks back into the left wing (will need some cosmetic surgery here to make it look good) and also glued the root back on. Plan is to run a couple of lengths of carbon tube about 6 inches into the wing from the root to give some extra strength here. Along with the gorilla glue I think it should be a reasonable repair as the main wing-joining tube is also giving this area some strength.

Also need to glue the wingtip back-on. This however is still stuck in the tree!


I don't really want to buy a new wing-set as the glider was used when i bought it. The wing-set will be approx 75% of what i paid for the glider to start with.

Will post some piccies soon.
eddie currents is offline Find More Posts by eddie currents
Last edited by eddie currents; Sep 04, 2012 at 05:44 PM.
Reply With Quote
Old Sep 04, 2012, 03:41 PM
.: Looking for Thermals :.
Ricardo RW's Avatar
Chile, Quinta Región de Valparaíso, Los Andes
Joined Jun 2002
864 Posts
Eddie, Sorry to hear that.
Ricardo RW is offline Find More Posts by Ricardo RW
Reply With Quote
Old Sep 04, 2012, 10:22 PM
I'm a Registered User
Evansville, WI
Joined Dec 2006
3,689 Posts
Quote:
Originally Posted by eddie currents View Post
Just crashed mine badly....

I gassed it coming out of a loop with full up elevator (due to approaching terra-firma) and hit a big tree at full throttle. It's a big old bird so it was moving at a fair rate. I think due to the size of the Diamond it was further away than i realized as i thought i had plenty of clearance between me and the tree.

Found the glider on the floor with the following damage:-

Fuselage snapped in half just behind canopy. Now gorilla glued back together.

Battery/rx tray snapped. Now fibre-glassed and gorilla glued back together.

Motor mount loose and cowling damaged. Had to hack the cowling off to fix the motor mount with, yes, more gorilla glue (and some ply..) Cowling glued back on. Motor tested and still runs straight.

Prop snapped both sides. Replaced with el cheapo version until it test flies properly

Right wing cosmetically damaged.

Left wing in shreds, the wing was separate from the glider when i found it with the following damage -
Wing joining tube at 30 degree angle instead of straight.
Wing snapped completely at root where the ply wing-mount terminates.
Wing snapped completely at wing-tip at end of aileron.
Both ailerons semi-detached.
Two big chunks missing and numerous dings in leading edge.

One of the two Rx antennas snapped.


Bizarrely, after all this, i still think it is fixable.
The fuselage (after fixing), right-wing and tail look good.

I've glued the missing chunks back into the left wing (will need some cosmetic surgery here to make it look good) and also glued the root back on. Plan is to run a couple of lengths of carbon tube about 6 inches into the wing from the root to give some extra strength here. Along with the gorilla glue I think it should be a reasonable repair as the main wing-joining tube is also giving this area some strength.

Also need to glue the wingtip back-on. This however is still stuck in the tree!


I don't really want to buy a new wing-set as the glider was used when i bought it. The wing-set will be approx 75% of what i paid for the glider to start with.

Will post some piccies soon.

Your damage sounds just like my first (and second ) crashes. Did your tail stay attached? Both times I really slammed the plane, the tail snapped off just behind the internal tube. I actually managed to bend my motor shaft the first time too. Since my ailerons partially detached like yours, I went ahead and put actual hinges on all the control surfaces. IIRC, I used 5 hinges per surface. I also used Gorilla Glue, and some boiling water to re-expand some of the crunched foam. I straightened the wing joiner time as best as I could, it's pretty straight again, but not perfect. The plane doesn't seem to mind. Keep at it, even if you don't get it back together perfectly, it will still fly like a champ
Bugman Jeff is offline Find More Posts by Bugman Jeff
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Art-Tech EF2000 any one have it j3tman Foamy EDFs 2 Oct 24, 2009 10:42 AM
Discussion art tech spitfire bomb! (: kieran3008 Electric Warbirds 2 Oct 15, 2009 06:57 PM
Help! Art-tech Yak 54 Center of Gravity Midknight69 Electric Plane Talk 3 Oct 14, 2009 10:21 PM
Discussion art tech spitfire ***** kieran3008 Electric Warbirds 0 Oct 12, 2009 03:21 PM