This thread is on my design of the Swinging Skelly. I didn't come up with the basic idea for this prop, I give credit to others here for that, but I did come up with this design which I believe is a very simple approach to building the mechanism.
MATERIAL LIST
1x6x18 oak base
(2) 2x4x9.5" uprights
2x6x24 seat
6' - 1/2" pvc
(3) 1/2" pvc tee
(2) 1/2" pvc 45 degree elbow
(2) 3/4" pvc female adapter
pvc glue
wood glue
(4) 3" deck screws
20' - 3/8" rope
3/4 x 2" wood dowel
2" - 3/4"ID vinyl or rubber hose
1/4 x 3" bolt
(4) 1/4" lock nut
(2) 1/4" nylon washer (1" diameter)
(2) 1/4 x 1-1/4" carriage bolt
Wiper motor
90 degree bracket for motor
PWM speed control
FIND A SPOT FOR THE PROP
Before beginning this project, it's important to make sure you have a tree with a fairly level horizontal limb about 11 or 12' off the ground. The limb should be at least 2" diameter. I used heavy duty industrial zip ties to secure the mechanism to the limb but you can use U-bolts or screws if you're not worried about harming the tree.
BUILD IT
Start with the 1x6x18 oak base. You can use 3/4" plywood if you don't have oak. I wouldn't suggest pine for the base, it's too soft. Make sure the base is cut with perfectly square ends. Cut the two uprights from a 2x4, 9.5" each.* Use a miter saw or some method to be sure the cuts are perfectly square. Use a drill press and a 1-1/4" hole saw to drill the holes for the pvc adapters. Center each hole in the uprights 1-1/4" from the top. A drill press is very important in this step so the holes are straight. The 3/4" female adapters I used are Charlotte and the "slip fit" end fits very snugly into a 1-1/4" hole. Use a block of wood and a hammer to install the adapters. The threaded end of the adapters face outward when you assemble the uprights to the base. Mark 2 holes at each end of the base for the 3" deck screws to fasten the uprights. Pre-drill the base for screws and use wood glue to assemble the uprights. Make sure they are square with the ends of the base. Follow the labeled picture for cutting and assembling the pvc. Use pvc cement and make sure you push each joint fully together. I highly suggest using glue instead of screws, screws may weaken the pvc and eventually cause a fracture. Be sure the outer vertical legs on each side are aligned when gluing and also leave a little end play so the assembly isn't tight between the uprights. The center leg of the pvc should be slightly angled in the direction of the outer legs, not straight down. I ended up using a 16" length of 3/4" aluminum channel to stiffen the pvc assembly between the uprights. That part of the pvc was flexing each time the roller pushed the swing. Probably not a problem but I wasn't happy with it. I used two hose clamps to secure the channel to the pvc. The roller for the wiper motor is made from a 2" piece of 3/4" hardwood dowel. Use a drill press to drill a 1/4" hole in the center. Cut a 2" length of 3/4" ID vinyl or rubber hose and insert the dowel. Use the 3" bolt, washers, and two lock nuts to secure the roller to the motor arm. I used the arm that comes with the FrightProps motor, it is 1-1/2" hole to hole. Be sure to leave a little play so the roller moves freely. I made a 90 degree bracket for the motor, FrightProps has them but a bit pricey at $20. Use the two 1-1/4" carriage bolts and lock nuts to secure the bracket to the base. You want the the roller to contact the center leg of the pvc when the outer pvc legs are straight down and the motor arm is at 7 o'clock (when facing the motor shaft). The motor rotation needs to be CCW when facing the motor shaft. When the motor is rotating CCW it will contact the center pvc leg close to the bottom and then roll up while pushing the pvc assembly outward and slightly up. The ropes on my swing are cut to 10' lengths with my base at 11' off the ground. The ropes are threaded thru the pvc and secured with a knot at the top. You may need to adjust the rope length to suit your situation.
I secured the skelly to the seat with drywall screws thru the pelvis and legs. The PWM control is essential to this setup, without it you won't be able to adjust the motor rpm to match the swing cycle. I used the low speed wiring on the motor and powered the PWM with 12V. For my setup, 21 rpms was optimal for the swing cycle. Optimal setting has the motor roller contacting the center leg when the swing is ALMOST fully rearward. Slight adjustments of the PWM control make a difference, go a little at time until you get the best swing.
One last thing to consider is a way to keep rain from ruining the motor and speed control. I made a "roof" from sheet metal and gave it a quick camo paint job to match the oak tree it will be installed in.
Good luck and happy swinging!
MATERIAL LIST
1x6x18 oak base
(2) 2x4x9.5" uprights
2x6x24 seat
6' - 1/2" pvc
(3) 1/2" pvc tee
(2) 1/2" pvc 45 degree elbow
(2) 3/4" pvc female adapter
pvc glue
wood glue
(4) 3" deck screws
20' - 3/8" rope
3/4 x 2" wood dowel
2" - 3/4"ID vinyl or rubber hose
1/4 x 3" bolt
(4) 1/4" lock nut
(2) 1/4" nylon washer (1" diameter)
(2) 1/4 x 1-1/4" carriage bolt
Wiper motor
90 degree bracket for motor
PWM speed control
FIND A SPOT FOR THE PROP
Before beginning this project, it's important to make sure you have a tree with a fairly level horizontal limb about 11 or 12' off the ground. The limb should be at least 2" diameter. I used heavy duty industrial zip ties to secure the mechanism to the limb but you can use U-bolts or screws if you're not worried about harming the tree.
BUILD IT
Start with the 1x6x18 oak base. You can use 3/4" plywood if you don't have oak. I wouldn't suggest pine for the base, it's too soft. Make sure the base is cut with perfectly square ends. Cut the two uprights from a 2x4, 9.5" each.* Use a miter saw or some method to be sure the cuts are perfectly square. Use a drill press and a 1-1/4" hole saw to drill the holes for the pvc adapters. Center each hole in the uprights 1-1/4" from the top. A drill press is very important in this step so the holes are straight. The 3/4" female adapters I used are Charlotte and the "slip fit" end fits very snugly into a 1-1/4" hole. Use a block of wood and a hammer to install the adapters. The threaded end of the adapters face outward when you assemble the uprights to the base. Mark 2 holes at each end of the base for the 3" deck screws to fasten the uprights. Pre-drill the base for screws and use wood glue to assemble the uprights. Make sure they are square with the ends of the base. Follow the labeled picture for cutting and assembling the pvc. Use pvc cement and make sure you push each joint fully together. I highly suggest using glue instead of screws, screws may weaken the pvc and eventually cause a fracture. Be sure the outer vertical legs on each side are aligned when gluing and also leave a little end play so the assembly isn't tight between the uprights. The center leg of the pvc should be slightly angled in the direction of the outer legs, not straight down. I ended up using a 16" length of 3/4" aluminum channel to stiffen the pvc assembly between the uprights. That part of the pvc was flexing each time the roller pushed the swing. Probably not a problem but I wasn't happy with it. I used two hose clamps to secure the channel to the pvc. The roller for the wiper motor is made from a 2" piece of 3/4" hardwood dowel. Use a drill press to drill a 1/4" hole in the center. Cut a 2" length of 3/4" ID vinyl or rubber hose and insert the dowel. Use the 3" bolt, washers, and two lock nuts to secure the roller to the motor arm. I used the arm that comes with the FrightProps motor, it is 1-1/2" hole to hole. Be sure to leave a little play so the roller moves freely. I made a 90 degree bracket for the motor, FrightProps has them but a bit pricey at $20. Use the two 1-1/4" carriage bolts and lock nuts to secure the bracket to the base. You want the the roller to contact the center leg of the pvc when the outer pvc legs are straight down and the motor arm is at 7 o'clock (when facing the motor shaft). The motor rotation needs to be CCW when facing the motor shaft. When the motor is rotating CCW it will contact the center pvc leg close to the bottom and then roll up while pushing the pvc assembly outward and slightly up. The ropes on my swing are cut to 10' lengths with my base at 11' off the ground. The ropes are threaded thru the pvc and secured with a knot at the top. You may need to adjust the rope length to suit your situation.
I secured the skelly to the seat with drywall screws thru the pelvis and legs. The PWM control is essential to this setup, without it you won't be able to adjust the motor rpm to match the swing cycle. I used the low speed wiring on the motor and powered the PWM with 12V. For my setup, 21 rpms was optimal for the swing cycle. Optimal setting has the motor roller contacting the center leg when the swing is ALMOST fully rearward. Slight adjustments of the PWM control make a difference, go a little at time until you get the best swing.
One last thing to consider is a way to keep rain from ruining the motor and speed control. I made a "roof" from sheet metal and gave it a quick camo paint job to match the oak tree it will be installed in.
Good luck and happy swinging!
) .
