Simple frame to support a single layer inductor. I personally used for WPT project. With the use of a standard pvc tube you can stack one after the other inductors maintaining the alignment and allowing testing variable distance among coils. Follow upgrades and further THINGS @ https://accedtech.wordpress.com/You can calculate the inductance based on the classic Wheeler’s formula for single-layer inductance (air core, tightly wound), which dates back to the radio days of the 1920s: L = 0.001N2D/((228D/2) + 254l) Where: L is the inductance in henry’s. D is the coil diameter in meters. l is the coil length in meters (>0.8radius) N is the number of turns. The diameter is measured from center of wire trough center of the coil and to center of the wire on the opposite side. This formula applies at ‘low’ frequencies (<3MHz) )using enameled copper wire (magnet wire) tightly wound. Small reductions in the inductance obtained can be achieved by pulling the turns apart slightly. This will also reduce self-resonance. Other combinations of wire and coil diameter may be tried but best results are usually obtained when the length of the coil is the same as its diameter. If you need good induction stability in the presence of vibration then wind the coil on a support made from a suitable non magnetic plastic or ceramic former and lock the windings using epoxy glue or other suitable adhesive