Design & build of Pencam-class photo platform

[Karl B²]

I've been working on & off for the past 5 months on a design that will replace the Slowstick for me when operating out of all but the most cramped LZ's. Two months ago I reached CAD stage, and for the last two weeks the balsa scraps and glue have been flying.

WS: 48", just under 400 sq. in.
Airfoil: modified E-193
Power: geared 300-400 class
Control: R/E/T/Shutter
Payload: 3 oz max

CF tailboom, pull-pull controls inside boom, surfaces & fuse built-up balsa/ply, wing built-up balsa/ply w/CF tape spar doublers, quick-release wing (NO RUBBERBANDS! :) )

Ideas for larger next-gen: 6-8 oz payload for larger CCD/AF, pitch leveler for camera, left-down-right aim on aux. channel, flaperons.

Karl

[Karl B²]

Tail items:

[Karl B²]

last for now:

[RMihara]

Hi Karl,

Very nice design there. I am wondering if you will be incorporating any dihedral in the main wing? The self leveling properties of such a design would be a plus. Of course if you wanted maximum lift then keeping the wing flat would be a better design no?

I like the angled rudder surface, has this helped in reducing the turning radius of the plane? I'm still learning the basics of plane design so please bear with my questions.

BTW, 0.02 on your self-leveling thought. You could attach the camera with a simple two-axis gimbal, that would not only give you pitch correction but roll as well.

Regards,
Roger

[Karl B²]

Hi Roger,

Thanks for the comments. Wing will have a constant chord 24" center section, with two 12" double-taper polyhedral tips. The taper and tip design on the tail uses a modified TLAR method called ILILT (I like it like that). The fuse including the boom will be over 40", with a tail moment arm of about 26".

Angling the rudder hinge line effectively adds a bit of up pitch, so that when holding a slow turn, the pitch angle (hopefully) won't need much adjustment.

I built up a gravity leveler (pendulum) test rig with a small RC car damper (shock minus spring, 1/2" stroke), and found that the pencam needed to be suspended about 4" to swing free with the damper working at about an 8:1 reduction using 10w silicone oil. Shorter length requires less damping, and 8:1 is about the geometrical limit with a simple extension strut.

A viscous suspension would certainly be simpler than struts, especially for a two axis stabilizer. At any rate, that would be for a larger craft, and using a commercially available optical wing leveler/copilot (FMA?) might be the simpler solution once weight is less critical.

Back to work,
Karl

[RMihara]

The wing sounds like a winner and I like your 'modified TLAR' method :D

Here is a drawing of the gimbal mount I mentioned. Given that the camera would be exposed to the elements (namely open air velocity - buffeting), I really like your approach using a damper based system. The single spring in this design could be modified (single-dual rate, coil dia., wire thicknes) to account for this effect but would not allow for self leveling as the spring rate increases...
I suppose I could increase the distance of the cameras moment of inertia away from the pivot point to account for any change in spring stiffness.

Back to (work) the drawing board. :D

Roger

[RMihara]

Oops, your plane shows the camera mounted in 'portrait' orientation... :D

[Karl B²]

I've GOT to get into 3D cad. I have DesignCAD 3D, not sure of the version, for Win 95. Just haven't installed it yet.

Yes, I'm using the Pencam SD, which takes landscape shots with the body horizontal. I'll be mounting it as shown in the attached pic. An electronic switch or remote servo-actuated switches would reduce the dimensions to be rotated.

I'll always need easy access to the USB port, SD memory cam, or batteries, and I went with the passively faired "notch" for simplicity. I may go with a thin sheet of ABS held with magnets to fully fair the cam.

Karl

[Karl B²]

Fuse construction started with a crutch of 1/32 ply with balsa & ply boom mounts.

[Karl B²]

Fuselage frame 95% complete. I have the upper portions sheeted with 1/32 balsa, and once I install the motor mount and LG hardpoints the rest of the sheeting will go quick.

Karl

[Karl B²]

Sheeted..

[Karl B²]

View of the wing saddle showing the battery platform. Also visible is the right thrust built into the front former. Wing will have either a dowel or tab in front to engage a hole or slot, rear will be retained with either a latch or internal rubber bands.

Running out of excuses to put off making the wing...

Karl

[Karl B²]

First mockup:

[Karl B²]

Another view:

[dmoran]

Kinnic:
Looking great. Now can you design me a gyro-stabilized ball mount for my onboard video camera??? (just kidding)
If you get up to Madison, let me know and we'll go flying.

Dennis Moran
dmoran@itis.com

[Karl B²]

Hey Dennis, I'll keep the flying in mind, though Madison is a 4 hour hike for me. Are you planning on attending the MARCEE (http://www.marcee.org/) meet in St. Paul this weekend?

I was going to use simple pull-pull bellcranks, but ended up going with a pulley/drum system. Only destroyed 2 meters of kevlar thread trying to find the best methods to route it through the boom and guide tubes :rolleyes:, but I got over that learning curve with plenty of thread to spare.

The pulleys on the surfaces are made of 1/32" ply. I chucked it in my Dremel and used a 150 grit block to turn it down. For the servos I'll make more of a drum than a pulley. The rudder drum will match the pulley for a 1:1 angular action. The elevator drum will be smaller by about a third for reduced throw.

Karl

Bottom view:

[Karl B²]

Side shot shows the pulley offset required by the reclining hinge line:

[Karl B²]

Look ma, no servo! Well, at least not attached to the camera anymore. Wired RadioShack # 275-016A switches parallel to the shutter & mode switches. Left stick triggers the shutter, right triggers the mode switch. Also wired a USB --> BEC plug, coming out of the battery cover, not visible in this shot.

Without the servo piggy-backing on the camera case, there will be room for it to rotate within the fuselage. I mounted the ball links more centrally on the ends of the camera.

Karl

[KeithLuneau]

Wouldn't a smaller pulley on the elevator give it more throw?

[Karl B²]

Yes, the smaller the driven (surface) pulley, the greater the surface throw. If the driven pulley is the same size as the drive (servo) pulley, the surface angular deflection will equal the output shaft angular deflection.

My Hitec HS-55's give about +/- 45 degrees. I'm targeting +/- 30 degrees rudder throw, and about +/- 15 degrees for elevator. The elevator drive will actually have to be about 1/3 the diameter of the driven, and the rudder drive will be about 75% the diameter of the driven.

The pulley system, as opposed to a standard pushrod/bellcrank, has no built in limits. The only mechanical limits on surface throw are the angles I sanded into the LE for hinging. The elevator will move +/- 30, and the rudder will move about +/- 45 degrees max. I'm setting the pulley sizes for just under these limits, and can always back off the ATV if this proves too sensitive.

Pros of this control setup: extremely light (good for long runs), virtually no slop, less possibility of binding than pull-pull bellcranks, true linear output with a non-computer radio, can follow more torturous path than pushrods by using idler pulleys and/or guide tubes.

Cons: more work to rig, can't be easily retrofitted due to interference issues between the pulley and the fixed surface, mechanical adjustment of throw requires a pulley change.

I've always been meaning to try it and the time was now. Like changing brake pads on a car, the first time takes the longest. :)

[Karl B²]

Got the camera mounted this weekend. Ball studs on the camera ends snap into nylon ball sockets. The sockets are attached to 1/2" threaded shafts, in turn attached to lengths of Sullivan nyrod buried in balsa stand-offs.

This shot shows the fuse bottom. The landing gear hardpoint will extend forward a few inches from the crossbrace over the camera. The bottom from there forward will be a removeable hatch.

Karl

[Karl B²]

View looking up at the bottom, facing the rear. Front cam mount and USB --> BEC cable exiting through the battery hatch are visible. The USB port will be accessible through the forward bottom hatch.

[Karl B²]

Looking up at the rear camera mount. Test photos of several angles assure that none of the fuse is visible. Camera has clearance to rotate 360 degrees on the ball mounts. The lower rear corner of the fuse behind the camera will be enclosed with either a built-up balsa or balsa-framed sheet ABS removeable cowl.

[Karl B²]

Landing gear is a one-piece 3/32" wire. To clear the camera, it follows the fuse sides then crosses above the camera.

The built-up balsa front hatch was fabricated once the gear was in place.

[Karl B²]

My wing-taster buddy is visible in the background of the previous shot. ;)

The motor is back in my Slowstick for an early July 4th getaway. Hope to find some golf courses and try out my polarizer-equipped Aiptek. Be back Friday!

Karl

[KeithLuneau]

Lookin' good. How much right thrust is in the fuse? It should work out ok, after you get to altitude and shot the motor off, hopefully very little trim changed will be needed. It's hard to trim a plane that's 1000+ feet in the air. LOL

[Karl B²]

I have 3* down and 4* right. The prop shaft is centered where it comes through the front former, so there's a lot of gearbox & motor angled left of center.

I'm already working on my 'magazine' type flight review: "climbs with authority, no trim needed!" :D

Karl

[eBird]

Originally posted by Kinnic^2
I have 3* down and 4* right. The prop shaft is centered where it comes through the front former, so there's a lot of gearbox & motor angled left of center.

I'm already working on my 'magazine' type flight review: "climbs with authority, no trim needed!" :D

Karl

Karl, here's a semi useless tip of the day:
For the "degree" sign, hold down ALT and press 2 4 8 on the numeric keypad. 3° 4°

[KeithLuneau]

Cool, where can I find some more codes like that? I'm assuming they are ascii codes?

EDIT - nevermind, http://www.asciitable.com/

[RMihara]

You could just fire up 'Charmap.exe' (Start-Programs-Accesories).

Click on the character you want and look for the 'Alt' code in the lower right corner :D


Roger

[larryw]

That is a really nice looking design, please post more picts as you complete it. I have 4 2 meter sailplane wings from the 1970's Id like to build a fuse for and yours looks like a winner.

I was going to switch my camera the same as you did, I even bought the micro switches, then decided that I didnt want to put batteries in the camera for power, but looking at yours I gather you tapped the servo voltage to power the camera, thus no batteries and you didnt have to wreck a perfictly good servo for a switch. I didnt think of that. Nice job.

[Karl B²]

Larry,

I am tapping power from the BEC, much the same as the electronic switches do. When I bought the micro switches, I bought a AAA battery holder as well, thinking to shift the battery weight to a remote location, then had a DUH! moment, and wired to the USB pins instead.

This would work well with a 2 meter wing, though the tail area would need to be enlarged a bit. (Not hard to do with TurboCad. :D) I've done so many mods and designing as I build that my original CAD has fallen well behind the real version. Once I flight test, I'll update it and can make it available.

eBird, I know alt keys for degrees, 1/2, 1/4, and several other figures I use regularly, but that trick just dudn't work with my laptop. If I'm too lazy to plug in my USB remote numeric pad, I'm too lazy to start Character Map. (But never too lazy to raise my antenna ;) )

Karl

[larryw]

Karl:
Thank you.
I have one wing from a Gentle lady 10.2oz about 5'10" with a nice dihedral, that's the best one. I never did learn to fly in the 70's and gave up after I crashed 2 balsa gliders with a highstart. One from an electrosoar, a 80's electric. Its 16.2oz. but a full 6ft. The other 2 are foam one taped one not covered. 5-1/2 ft.

[Sparky Paul]

Or, you could use tape.... :)
See the inflight image in the ZAGI™ thread in Open...

[TStokes]

Kinnic,

How's it going with your plane???

I saw this one at NESail - and it reminds me of your design. I was thinking of getting it to see if it was a good AP design. I have an EZ400 that I like for AP.

Searches for this model come up with nothing. Anybody know anything about it???

http://www.nesail.com/cadetacro.htm

Tom

[Karl B²]

Tom, the Cadet Acro looks interesting. Link was bent: text was right but the link was just "http:///".

http://www.nesail.com/cadetacro.htm

It's about the same size, a bit smaller span & area. Hope my weight is similar, though the camera and larger battery are a big component. I like the large ailerons, which could double as big flaps, though a larger fin/rudder might be needed for STOL operations.

I haven't worked much on the project due to the holiday and recovery period afterwards. Thinking more and more about ailerons, though I would need to resurrect my 6 channel radio with a new battery, reverse the RX shift, and get a new crystal. The Airtronics 6 ch. Vanguard has 2- and 3-position auxilliary channels which would work for shutter and either flaps or camera oblique angle

Karl

[Sparky Paul]

all the photo planes I draw up tend to evolve to this shape...
camera(s) in front, pusher motor. hand-launch.
any old wing... 2M, 100"...

[Karl B²]

I wish I had a 2m wing I could use with this. As it is, I'll probably end up rigging the Slowstick wing in place for early test flights.

I improved my servo operated shutter switch a bit by replacing the Radio Shack "micro" switch with a small button switch out of an old electronic stopwatch. They're also available in just about any computer mouse, as well as joysticks.

[Karl B²]

Camera servo as mounted on the Slowstick. The plane is upside down in this shot, and the servo is retained with foam mounting tape and two small wire ties just in front of the flight servos. I didn't bother wiring a second switch for the mode button, as I never used it during the several flights it was active.

[Karl B²]

Been away from this project for awhile, busy with other pursuits. No new pictures ATM.

Tail Control
The pull-pull system worked wonderfully with the kevlar threads running in a direct line. Once they were threaded through the labyrinth nylon guide tubes in the stabilizer pylon however, the tension became too great for smooth action.

I next tried .040 CF rods running through several short nylon tube guides within the boom tube. The bends required to meet the servos and exit the tail also caused binding, so add two carbon fiber rods to the roll of kevlar thread in my "Now What?" pile.

Sullivan micro cables to the rescue! I glued two ½" lengths of standard size inner nyrod together side by side, and threaded the cable sleeves through them. I pressed the nyrod guide assembly into the tube, almost to the tail, and extracted the ends of the sleeves. Another glued pair of short nyrod pieces guide the sleeves at the forward end. I tinned 1" of each cable end, bent a 90° angle at the tail, and used EZ connectors & micro snap links to attach.

Fuselage
The CF spiral wound arrowshaft engages tightly in two main crossmembers right below the battery platform, and passes through a built-up block of ply with a nylon strap. Tightening the strap screws secures the boom, and allows removal for maintenance.

After sandwiching the motor mount between the gearbox and motor and adjusting the mesh, the ESC fit adjacent to the motor. Two balsa crosspieces with 1/32" ply skins carry the rudder, elevator, and shutter servos just aft of the motor/esc. All servos are inverted, and easily accessible through the bottom hatch. The rx is temporarily installed on the battery platform, and will eventually be mounted to the bottom hatch, just below the servos. A Dean's whip antenna attaches to the inner fuse side with velcro just forward of the wing and exits the top at a rearward angle.

Wing
I still haven't started the wing. Since my Slowstick is devoid of equipment at this point, I cut the aluminum SS fuse just forward of the LE bracket and aft of the TE bracket. I screwed two ply crosspieces to the SS servo brackets to bear the SS wing mount assembly on the new plane. Rubber bands hold the contraption to the wing saddle. Because the saddle is only 9" and the SS wing chord is nearly 12", the CG will be slightly forward even with the battery all the way back on the platform.

Next Steps
The SS hybrid (mongrel is more like it) is essentially ready to fly. I still have yet to cover the fuselage, but that's less of an imperative than it would be with a glow engine buzzing away. Check that thought - just had to chase one of the cats away, and found she put a few "speed holes" in one prop tip.

I'll grab some pics in the next day or so.

Karl

[Extremeone]

Here is a dual micro-switch that I rigged up 3 years ago when I wanted to run two video cameras in the same aircraft. A few of the electronics guys were working on video switches to do basically the same thing. I used the same transmitter, wired two cameras to it in parallel and used this device to switch the +5 volt supply between cameras. I just moved the two position tx switch (could have been any control) and the Servo-switch rotates full throw and locks one switch out while turning on the other, then does the opposite going the other way. I didn't have to worry about both getting turned on accidently. It works really well as a dual switch if you have any use for it.

Regards, John

[Extremeone]

Pic 2

[Extremeone]

Pic 3

[propfan]

Very clever! Now I have to think up something I could use that for ;)

[Extremeone]

I'm going to use it for the purpose it was designed, to switch between two video cameras in my sailplane. One looking fore, the other aft. All while taking still photos out the side. I will probably also, on occasion, use the aft mounted one boresighted with the still camera to aim more accurately.
John

[Karl B²]

John,

A video downlink for aiming would work well. It would be nice to have a brow mounted semi-transparent HUD over one eye, though a little LCD tv monitor strapped to the TX is more realistic.

Here's my servo bay. At the left can be seen a cutout for the Pencam USB, and the MiniAC & Phoenix 25 are at right.

Karl

[Karl B²]

Here is the aft fairing that will go behind the camera. Made with 1/32" sheet, 3/32" stringers, and 1/16" formers.

[Karl B²]

Fairing with sheeting:

[Karl B²]

Tabs will hold the front, with a magnet securing the back. Here it is positioned in place.

[Karl B²]

The boom is clamped by the strap, allowing removal/adjustment.

Karl

[Karl B²]

All covered:

[Karl B²]

Here she is with the hatches open. The rake angle on the gear puts the straight landing compression loads in line with the CG, and the strut runs right up to the bottom of the battery platform. The plan was to not repeat that Slowstick LG "dribble" as the gear bounces fore and aft along the ground. The angle and thicker wire (3/32) should accomplish that.

[Karl B²]

Elevator pylon & control linkages:

[Karl B²]

Mockup with Slowstick wing.

[Karl B²]

Are those surfaces too small...

[Karl B²]

...or is that tailboom too long?

CAD layout for the wing is almost done. The outboard panels will reflect the tail design, so this will be my first tapered wing built from scratch.

Karl

[Sparky Paul]

The surfaces look OK, but the boom.... looks anoretic!
I've found those things can (will) bend with flight loads at speed. Down.

[Karl B²]

I just read that about the Wingo. I'll have to see if I get any reversal problems. Could always inject the boom with polyurethane. ;)

Karl

[Ironsides]

Karl:

You could put fishing line braces from the top and bottom of the fin to the tail boom at the trailing edge of the wing. Those lines would act as a safety to prevent the Wingo tuck.

David

[KeithLuneau]

That plane is coming along nicely! Looking forward to hearing how it flys, and seing pictures from it!

Keith

[Karl B²]

Thanks, Keith. First flights are about a week away.

Here's the wing construction. Span is now targeting just over 60". The flat center section is about 34", with 15" polyhedral tip panels. The CF tape spar caps are 48", and will extend unbroken across the dihedral breaks to halfway out the end panels.

I have the center panel complete save for the top sheeting, and the spar is every bit as strong as I hoped. It's just flexible enough that washout can be added via setting the Solite film.

Wing construction photos will follow.

Karl

[Karl B²]

Overview of most of the center section. The large bays will be diagonally braced with the leftover kevlar thread once the wing is complete.

I was going to add ailerons, but will keep the weight and complexity down for this version.

[Karl B²]

Rib/spar closeup.

[RMihara]

Hi Karl,

Your project is coming along nicely :) Now hurry up and get it done so you could make a kit for all of us! :D

Roger

[Karl B²]

I'm hurrying! :) I have to take a break every three days to shed my CA skin...

I'm finding out that it's just a little more complicated when the structural details have to be figgered out as I go.

[Karl B²]

Wing is nearly complete. After installing the last tip sheet & internal bracing, sanding will go quick, then covering.

[Karl B²]

quarter view:

[Karl B²]

With the top sheeting in place, there's almost no torsional flex. Fortunately I found this out on the center section, so I blocked up the tip panels for approx. 3/16" washout at the end.

Karl

[Karl B²]

Complete! Wing is held with a CF dowel in front, and a single socket head bolt in the rear. I'd like to have a 1/4 turn lock type of fastener, as I have to remove the wing to get at the battery, but this will do for now.

[Karl B²]

After John (Extremeone) had the issue with transparent covering tinting his images, I was concerned that my plan for yellow transp. would affect the images. I wrapped the covering around the wing, held it so that the sun shone on the lens through the covering, and took a bunch of test shots. Doesn't seem to be a problem, so I went ahead. (Besides, I didn't want to have to wait on an order for more covering.)

First flights might be tonight. With the battery centered on the plate, the CG is about 1/3 chord back from the LE. I'll shift it forward for the first flights. I've also gone from a 9x4.7 to an 8x6 APC-sf prop.

Not ready to be nervous, but I'm sure I will be by the time I start loading the car...

Karl

[Trikster]

That looks great! I hope all goes well and that you end up with quality pictures. If so, you will have lots of people clamering for plans/kit. GL on the maiden!

[KeithLuneau]

Lookin good as usual! I like that white wingtip for orientation. Should come in handy for those high altitude flights. :)

[Ironsides]

Karl:

Good looking bird.

David

[Karl B²]

Thanks guys. Batteries are charging as I type this, and the winds are light enough for a maiden this afternoon if the rain holds off.

I managed to reroute the ESC wiring so that the battery can be disconnected by removing the aft lower hatch. Still need the wing off to change batteries, but power on/off is pretty easy with just a magnetically secured hatch.

Plenty of ideas in mind for mods/next generation:

- reduce dihedral and add flaperons to center section for better confined landing areas
- enlarge fin/stab (the original area calculations were correct, but the wing grew from 380 to 565 sq. in. and the tailboom was shortened for mounting reasons.)
- simplified fuse design & construction methods. Building and designing around the crutch was handy, as I could place components and build the fuse around them. Unfortunately, the parts count is high and not worth the minor strength/weight improvements it yields.
- provisions for the PJS series of outrunner brushless. I'd really like to be able to shoot while the motor is running...
- size the fuse for the upcoming micro CCD cameras now becoming popular.

I doubt I'll ever kit this, but plans &/or a short kit (laser cut parts) might be an option.

Excuse me, my batteries are done and I have a plane to maiden. Knock wood!

Karl

[FLYWINGFAN]

Good Luck!
-Sam