...continuing from Pt1 - - >
- Take the 5.8mm diameter brass tube pick one end and try to sand at least 5mm into the tube (on the inside). Mount the brass tubing on the vice without squishing it and apply a thin layer of solder on the inside.
- Ignite the flame torch, take the 4mm threaded tube (holding it by the screw) and move it on the soldered end of the 5.8mm diameter brass tube which should still be mounted on the vice. Using the flame torch heat-up both tubes and carefully insert the 4mm threaded tubing inside the 5.8mm tubing until is fully inside. Use a pair of pliers and insert the brass tube by holding the end of the screw that sticks out. Hold the threaded tube levelled inside the 5.8mm tube until the solder settles. If you do not have a flame torch use a candle, your soldering iron and your patience
. Remove the screw. The end result will be the cylinder of your linear actuator.
- The cylinder length should be equal to: the actuator’s desired working length (stroke) + length of the 4mm threaded tube which is inside the 5.8mm tube + 10mm for the mounting hinge at the cylinder end.
- The thread length should be: the actuator’s desired working length (stroke) + length of threaded tube which is inside the 5.8mm tube + length of the thread which resides inside the servo casing, which is model-dependant.
- Take the non-threaded/non-soldered side of the cylinder and drill a 2.5mm hole through, 5mm from the tip.
- Cover the entire length of the cylinder with heat-shrinking tube and cut-off any excess bits. The 2.5mm through holes made earlier on the non-threaded side of the cylinder are now covered. Use the drill again to expose them and tap them through, using the M3 tap. Screw a 20mm long M3 studding or simply cut-off the head of a 20mm long M3 screw. This will act as your cylinder mounting hinge.
- Take the 4.8mm styrene tubing and M4 tap it 10mm deep. Cut a small ring 5mm in length and screw it in the M4 thread fully, from the side of the nut that was in contact with the washers (long side of the M4 thread)
. This will act as bushing between the thread and the servo’s case bottom cover. Ideally you should use nylon, copper or metal bushing.
- Secure the motor cables inside the servo casing using a glue-gun and use heat-shrinking tube to cover them. Assemble the servo including the thread, the styrene bushing and the washers.
- Screw-on the cylinder and you are good to go!
A video of the actuator:
For those of you that have watched my video on the MTR Rover and read the posthttp://126.96.36.199/~sor/robotforum/index.php?topic=9693.0
will understand where the idea of hacking the servo came from
Soon I will be posting assembly instructions, code and schematics on how to modify a standard servo to get full PID speed and position control with 10-bit resolution over 360 degrees – continuous
I look forward for your comments!