It's really easy.
1 Suspend a servo from the bridle
2 Add yacht steering, to pull the back edges
I built this in my quest to open source airborne wind energy. (Making power with kites has become efficient)
A steered single line lifter was needed for my daisy power project, but
It also helps in Kite Aerial Photography when framing is everything and you want your kite held to one side,
It can help penguin toys realise their dreams and fly... Well that's what my kids wanted it for... So many practical uses.
I needed to buy 3 parts
1. A lifter kite. I used the Jumbo powersled 36 joker. It's really strong. Manfred from the shop is so helpful. ~£70
2. A remote control setup. I found a Futaba skysport 4 on ebay for ~£10 but you only need 1 channel of control.
3. A strong multi turn sail winch type servo. The Hitec HS-785 HB didn't flinch once. awesome piece of kit. ~£20
I also used
Kite tether line for steering
2 caps from an oil spray can for beefing up the servo line horn.... you'll see.
some light strong sheet material ~20cm x 20cm to cage everything in.
You can get an idea of the setup in this video. (note we are only building the top piece of this)
Step 1: Sail Winch Steering Controls
Test that your controller can make your servo go 5 turns clockwise, re centre and go 5 turns anticlockwise.
cool... play with it for a while because servos are cool... you probably only need 3 turns but lets stick to 5.
A sail winch servo releases one line as it winds another in. It has two pulley sheaves fixed together on the servo shaft.
With the servo centred, one sheave has 5 clockwise turns of line, the other sheave holds 5 anticlockwise turns of line. At full rotation 1 sheave will hold 10 turns whilst the other will be totally unwound.
In order to steer the kite we will pull the bottom edge one side and release the other side.
The difference in length between the two control lines will deform the kite, making it steer.
Each sheave has a small hole in the wall. See below. Thread one end of a control line through the hole and set it in place with a figure 8 stop knot. Control lines can be thinner than the 3 bridle lines. Control lines do not pull as much tension.
10 turns (of the line I chose) was too thick to stay on the sheaves... So I widened them with the tops of two spray cans.
Step 2: Controller Build
Ok, how to hold the battery, radio receiver and servo together.
When together they hang below the bridle attachment point, The servo control lines should stay on the double pulley yacht control. You can do this better than I did.
I cut and bent the housing of an old computer power supply. The sheet wrapped around the servo, and left space for the receiver to tuck in below. I could also bolt the servo onto the casing.
Threading the control lines through the grill holes is a convenient way to keep them close to the sheaves.
I drilled a hole in the rear web. When suspended by this point the control lines point down. This is ok as they are less prone to jumping off the sheaves. When attached, tension from the kite on the control lines will lightly pull the whole set forward.
See the second picture.
The green stuff is sugru. Used here for smooth edges.
Duct tape, yeah it's a classy rig. Used here for sort of waterproofing, holding things together, keeping the antenna hanging right, padding... and getting the look right.
Step 3: "Measure" Some Lines
The powersled is a really stable design. Air pressure holds the sides of the kite out. The windsock (or drogue) holds the kite pointing steady into wind (it also doubles as the bag for the kite)
The bridle lines on sled kites are long. Short bridles would force the kite to collapse inward.
When the kite is "flying" You want the control lines to snugly hold onto the outer edge tail connection points. Too tight; the kite may not lift so well and the servo will have to work harder. Too loose; the lines may shake loose on the servo horn and response will be really sluggish if there is slack line to wind in.
You can see in the youtube video that I slung my controller in the loft and suspended the kite below it to get an idea of how long to make my steering control lines... you don't need to do that. Just lay the kite on the floor, lay out the bridle lines and guess. Like in the second picture below (side on view)
If anyone really wants me to report on mm accuracy... I'll measure my rig for you. but it's pure guess work and I actually re tie it every time I use it... works fine every time so far.
Step 4: Tips
So when you pull on the right hand side of a LEI (Leading edge inflated) surf kite or ram air kite. pretty much and controllable stunt kite.. The kite goes to that side.
And that's exactly what you'd expect to happen with this kite... but
I'm going to guess (others know better) When the tether pulls the tail, the angle of attack increases as does the lift/drag ratio on that side, giving it more lift than the other ... thus rotating the kite to the other side.
With the drogue on you can leave the kite sitting downwind steady all day, until you decide to take control.
When you apply the control, be gentle and the kite balances against the drogue on the edge of the wind window... perfect for lining up your photo.
If you do happen to be rough on the control, like my kids were, you can loop a lifter kite.
enjoy... and vote now please
I have plenty more bonkers kite designs. Will write them up here soon