Our biggest EHD thruster to date. The main aim is not to show 'the bigger the better' concept, but to form a structure which has a high ratio for element length to structure weight, minimum number of sharp corners, minimum lengths of 'dead supports' to hold the structure and wire, and that combines the advantages of the low profile thruster cell and be modular. As you see in the photo above, I have avoided sharp edges and multiple corners (triangular cells), resulting in a higher thruster element length to weight ratio. The top frame which carries the fine wires is vertically adjustable by sliding pieces of plastic drinking straw sections over the vertical balsa supports.
Total element length = 1834 cm
Total weight = 70 g
Thrust measured with my present overloaded power supply:
70 g (thruster weight) + 10 g additional payload
This occurs at 19 kV pulsed 20 kHz, 80 Watts. This EHD thruster is designed to work at maximum efficiency at about 40 kV. I am sure this thruster will lift payloads over 100g with a siutable power supply.
Dimensions for this thruster cell are as follows:
90 mm between cells
5 sectors have these dimensions: 93, 82, 72, 61 cm
1 of the sectors has dimensions: 88, 77, 67, 57 cm
These dimensions enable the 6 vertices to lie on the circumference of a complete circle, thus making the cell modular. Kind of a honeycomb structure.
Wire NOT directly on top of foil, but same as my low profile thruster, i.e. it sits above in between each 2 foils. This was found to achieve twice the performance of normal wire on foil - refer to low profile thruster. Wire to foil distance, manually set from 2 cm to 5 cm above foil layer. Balsa used was of round cross section of 5 mm, stripped in two along
its length. Foil skirts 30 mm. The 90 mm was inherited from my low profile thruster design, which was found to be the best meadurement by experiment some time ago, based on a 40 kV supply. Diagonal (effective) air gap between wire and foil is set to about 5 cm.
So the total height of the low profile becomes: (52- (9/2)2)1/2 = 2.18 cm for 40 kV ... and that's from where the name low profile comes, since you can stack more than twice the number of thrusters vertically on top of each other, as you would with 'normal' wire-on-foil style. Each thruster can lift >100 g, and a stack of just 50 cm high would lift >1 kg. (foil=3cm, vertical gap ~ 2cm).
This cell is based on the spiral hex thruster shown above. The difference is mainly in the way that corona wires are supported over the foil. Each section has now got a further support at the middle of the wire which eliminates the problem with wire sagging, which results in spark over and possible destruction of part of the thruster. Also, corona wire has been changed to 0.2 mm nichrome wire, which is much more rigid than the 0.1 mm copper wire. The six vertices have been connected to a centre point with additional balsa which made the whole thruster much more rigid and with better shock handling. This thruster is driven by my 1000 Watt power supply.
The whole structure now weighs 98 g. Air gap was set at 50 mm, and this enabled the thruster to handle up to 38 kV before sparkover, at which point it lifted an external payload of 70 g (total lifting force of 155 gF). If the air gap is increased to handle 50 kV, the external payload capacity should now exceed 100 g. See spiral version V2.0 below.
|This thruster is a revised version of V2.0, the only difference being the air gap distance. This one has sliding straws which can move the corona wire between 60 mm to 90 mm from the top of foil. This device is driven by my 1000 Watt power supply.
The whole structure weighs 98 g, same as V2.0. Air gap was set at 70 mm, and this enabled the EHD thruster to handle voltages over 40 kV as required, at which point it lifted an external payload of 102 g (total lifting force of 198 gF). In the photo you can see the 102 g external payload stainless steel nuts, which are inserted in each balsa vertice as shown in the photo. When powered on, it goes up very smoothly and well balanced and its maximum payload surely exceeds 100 g. You may find further experimental data and movies for this thruster in Experiment 14