Enhancing the performance of the Cyber Sky Parachute Using Li-Polymer batteries: Simply substituting a 12C 7.4V 800mAh Lithium-Polymer rechargeable battery, in place of the standard Ni-Cd 7.2V 700mAh battery, will raise the maximum effective payload of the Cyber Sky Parachute from one ounce (28 grams) to 5-3/8 ounces (152 grams). The 800mAh 7.4V Li-Po battery weighs only 5/8 ounces (44 grams). And, more importantly, the standard 4 pitch propellor does not have to replaced with a 4.7 pitch prop (see next section, below). Lithium-Polymer batteries were actually my first choice for enhancing the performance of the Cyber Sky Parachute, but there was a delay in shipment of my new Li-Po battery and charger, so I opted to go ahead and test a 4.7 pitch prop instead. But payload, or ballast, must be added to the craft if the standard Ni-Cd battery is replaced with a lighter Lithium-Polymer battery. Don't be tempted to lighten the over-all weight of the gondola, since motorized parafoil models need a specific minimum gondola weight to fly properly, or the propellor thrust and torque will cause the rig to loose control. ------------------------------------------------------------------------------ Switching to a 4.7 pitch prop: October 4, 2006 Below is my bench test of the standard 9 inch - 4 pitch prop compared to a special 9 inch - 4.7 pitch prop. Standard Ni-Cd 7.2V 700mAh batteries were used. Specified to produce 3-1/2 minutes of full power (with the 4 pitch prop), the battery weighs 5 ounces (142 grams). Standard Mabuchi RK-370SD Motor was used. The motor is capable of operating on up to a max of 9.6 volts. Weight of Gondola with battery: 15-3/4oz(450g). Weight of entire Cyber Sky Parachute (battery and chute): 19 oz (551 g) Prop tested: E-flite 9x4.7 Slow Flyer Prop EFLP0947 (Identical fitting to the stock 4 pitch propellor: 3mm shaft and M3 prop nut) Ordered from www.wholesaletrains.com Tentative Conclusions: - Operating temperatures over 50 degrees Fahrenheit, above ambient, may red line (burn out) the Mabuchi Motor. But a 7.2V 1100mAh Ni-Cd battery is also sold as an accessory to the 700mAh battery, which would only run the motor much hotter, even with the standard 4 pitch propellor. So the standard Mabuchi RK-370SD motor can obviously get much hotter, and not burn out. I just don't know how much. Maybe someone else has a 1100 mAh Ni-Cd battery they can bench test, and up the maximum operating temperature that we can safely push the limits to on these things. - 4.7 pitch prop shows much potential for lofting payloads, but with a shortened flight time. The Cyber Sky Parachute's top speed of 10mph will probably not be increased by the 4.7 pitch prop. The stock 4 pitch prop can barely loft a maximum payload of 3 ounces (85 grams) and a maximum effective payload capability of 1 ounce (28 grams). The 4.7 pitch prop has potential of a maximum effective payload capability of, maybe, 2-1/4 ounces (63 grams), but tests so far have lofted 3-1/8 ounces (90 grams) to a respectable altitude. - The 4.7 pitch prop turns counter-clockwise, requiring a basic switch of the wires to the motor. The wires were cut and 22-18 guage wire quick disconnects were soldered in place and the motor wiring was re-routed to the outside of the gondola, to allow a quick change-over back to the original 4 pitch prop (clockwise). An extra stainless steel M3 metric nut was added to the end of the propellor shaft to ensure that it doesn't unscrew itself. - The internal brushes in Mabuchi 370 motors suffer a shortened lifespan when the polarity is reversed and the motor is run "backwards". But the E-flite (#EFLM210) motor, at $ 7.50, is an economical replacement. - To keep the motor running cool with the 4.7 pitch prop, heat sinks were fashioned from standard .026" aluminum flashing. Two pieces of aluminum, 20mm wide, were formed to a snug wrap-around fit around the motor, to nest between the clear plastic end caps, as half-circle pieces. Once the motor, with its new wrap-around heat sink, was bolted back into the plastic gondola, four additional, external, cooling fins were fashioned from the same aluminum sheet. Measuring 30mm x 15mm + tabs, the tabs insert into the existing motor vent holes, making metal-to-metal contact with the new aluminum heat sink around the motor. Initial flight tests with 1600mAh NiMH packs suggests that the lower two external cooling fins need to radiate more heat and need to be increased in size to 30mm x 20mm + tabs. - High capacity (Li-Po) batteries, above 700mAh, will require a new bench test, with the 4.7 pitch propellor, to better appraise the proper time to throttle back and cruise at a slower motor speed, and avoid motor burnout. Disclaimer: - Test temperatures were measured of the outside metal casing of the motor. It was not tested as to how high the temperatures reach within the wiring inside the motor, where a burnout would actually take place. - Test temperatures measured for the 4 pitch prop were made WITHOUT the custom heatsink. Test temperatures measured for the 4.7 pitch prop were made WITH the custom heatsink. The 4.7 pitch prop may well have burned out the motor if the custom heatsink had not been installed beforehand. Standard E-flite 4 pitch prop: 4.7 pitch prop: Time Thrust Temperature Thrust Temperature (min:sec): (oz/grams): (Fahrenheit): (oz/grams): (Fahrenheit): 0:00 8oz(228g) 70deg 9-1/8oz(260g) 70deg 0:15 8oz(228g) 70deg 9oz(255g) 70deg 0:30 7-3/4oz(220g) 71deg 8-7/8oz(250g) 71deg 0:45 7-3/4oz(220g) 72deg 8-5/8oz(245g) 73deg 1:00 7-3/4oz(220g) 74deg 8-1/4oz(235g) 75deg 1:15 7-5/8oz(217g) 75deg 7-7/8oz(225g) 77deg 1:30 7-3/8oz(210g) 76deg 6oz(170g) 79deg 1:45 7-3/8oz(210g) 77deg 5-7/8oz(165g) 81deg 2:00 7-1/8oz(205g) 78deg 5-5/8oz(160g) 82deg 2:15 7-1/8oz(205g) 79deg 5-5/8oz(160g) 84deg 2:30 7oz(200g) 81deg 5-1/2oz(155g) 85deg 2:45 7oz(200g) 82deg 3-3/8oz(95g) 87deg 3:00 6-7/8oz(190g) 83deg 3-1/4oz(90g) 87deg 3:15 6-1/2oz(183g) 84deg -Stopped- 88deg 3:30 6-3/8oz(180g) 85deg 93deg 3:45 5-7/8oz(168g) 87deg 97deg 4:00 5-1/2oz(156g) 88deg 103deg 4:15 4-3/4oz(135g) 89deg 107deg 4:30 4-3/8oz(125g) 90deg 110deg 4:45 3-7/8oz(108g) 91deg 112deg 5:00 3-1/4oz(90g) 92deg 113deg 5:15 2oz(55g) 94deg 114deg 5:30 1-3/8oz(40g) 95deg 114deg 5:45 1-1/8oz(30g) 96deg 115deg 6:00 7/8oz(25g) 97deg 115deg 6:15 3/4oz(20g) 98deg 115deg 6:30 1/2oz(15g) 99deg 115deg 6:45 -Stopped- 101deg 115deg 7:00 102deg 7:15 103deg 7:30 107deg 7:45 110deg 8:00 113deg 8:15 115deg 8:30 116deg 8:45 117deg 9:00 117deg 9:15 117deg 9:30 118deg October 5, 2006 I did three test flights today with the 4.7 pitch prop and the results were mixed: The first flight: Results scrapped. See more recent flight, below. The second flight: Results scrapped. See more recent flight, below. The problem seemed to be that, for those two flights, the antenna wire had been scotch taped around the propellor guard, disrupting the natural resonance of the specific antenna length. Also, the chrome plating on the plastic propellor guard can interfere in the performance of the antenna, I just didn't realize that it would be that bad. That was obviously the motor performance problem. I removed the tape and let the antenna hang and flow freely again. I would have corrected the problem before the second flight, but felt that the 2.4 GHz video transmittor was somehow creating interferrence with the 27 MHz radio control receiver, due to its close proximity. The third flight, I lofted no payload, but used a 7.2V 1600mAh NiMH battery pack, weighing 6 ounces (170 grams). Although of a higher capacity than the 7.2V 700mAh Ni-Cd battery, the NiMH battery is 1 ounce (28 grams) heavier and lacks the high-discharge punch required for a quick get-away, to clear the trees and buildings. But, this time, the motor in the gondola purred along beautifully and I even chose to throttle back to half throttle, which actually improved the climb rate. The rig then went on to perform my highest and longest flight duration ever with the Cyber Sky Parachute. I'm not sure whether to give the 4.7 pitch prop the credit -or maybe a freak thermal. But the motor just seemed to run on forever before finally exhausting the battery. Upon landing, the motor was not even warm to the touch. A good sign. The 4.7 pitch prop and the 7.2V 1600 mAh NiMH battery seem to be a good combination. October 8, 2006 Today I lofted a digital camera rig, a total of 2-1/2 ounces (72 grams): Innovatech digital camera 3/4 ounce (22 grams) + two AA NiMH 1.5 volt batteries 7/8 ounce (25 grams) + a 60 second windup electrical timer, normally open, salvaged from an old Krups coffee grinder 7/8 ounce (25 grams). Using the stock 7.2V 700mAh Ni-Cd battery and the 4.7 pitch prop, the Cyber Sky Parachute climbed very quickly, with power to spare. By the time the 60 second timer activated the digital camera, the Cyber Sky Parachute was at an impressive altitude and I was able to cut back on the throttle. I made a total of four flights today, two with the 7.2V 700mAh Ni-Cd battery pack, and two with the 7.2V 1600mAh NiMH battery pack. Three of the flights were made in a busy local park and I chose not to loft a camera, went for performance and flight duration instead. The results were fantastic, quickly clearing trees and making tight turns -without losing altitude. I will probably use the 4.7 pitch prop from now on, since the performance is clearly superior to the standard 4 pitch prop. The trick, with the 4.7 pitch prop, is to use just enough throttle to get the job done at all times. Too much throttle and the Cyber Sky Parachute will simply take on the attitude of a high powered stall, simply wasting energy and not performing any better. Upon reaching cruising altitude, I now simply set the throttle trim to maximum, which is often just enough to maintain altitude and cruising speed, adding slightly more main throttle as needed. With the 7.2V 1600mAh NiMH battery pack, this increases the flight time to equal that with the standard 4 pitch prop. When using the 7.2V 700mAh Ni-Cd battery pack, I have a digital timer set on the transmittor, sounding an alarm at 3 minutes, a reminder to bring the Cyber Sky Parachute in, right away, since it dies very quickly, a little after 3 minutes, and the Cyber Sky Parachute is barely controllable, even at a glide. But this only happens with the 7.2V 700mAh Ni-Cd battery pack. As per my earlier conclusion, the 4.7 pitch prop and the 7.2V 1600mAh NiMH battery pack is the optimum combination. Initial flight tests with 1600mAh NiMH battery packs suggest that one minor modification needs to be made: the lower two external cooling fins need to radiate more heat and need to be increased in size to 30mm x 20mm + tabs. October 10, 2006 Today I lofted a digital camera rig, a total of 3-1/8 ounces (90 grams): Spypen 1.3 Megapixel digital camera 1-3/8 ounce (33 grams) + two A23 alkaline 12 volt batteries 1/2 ounce (26 grams) + 555 Adjustable Interval Timer Circuit and A23 battery holder 1-1/4 ounce (31 grams). Using the stock 7.2V 700mAh Ni-Cd battery and the 4.7 pitch prop, the Cyber Sky Parachute climbed quickly. The Cyber Sky Parachute reached a respectable altitude and I was able to cut back on the throttle, as the Spypen camera took pictures on a time-lapse mode. ------------------------------------------------------------------------------ Opting for custom made 7.2V DC-to-DC converters instead of heavy batteries, to power digital cameras and lighten the payload. There are numerous links in our Yahoo! Groups site that provide custom circuit board schematics for this. ------------------------------------------------------------------------------ The 27 MHz radio control unit for the Cyber Sky Parachute was designed to operate on 12 volts DC. That means 8 AA alkaline batteries of 1-1/2 volts each. 8 rechargeable batteries (Ni-Cd or NiMH) batteries may be used, but they only provide 9.6 volts. The rig will fly, but tend to steer to the right, since it senses that either the transmittor is getting weak or getting out of range, and sending it into its emergency landing mode. It's a built in feature that prevents losing the rig. I just got tired of setting the trim all the way to the left, and using body english on every flight. I have wired an external battery jack, and velcro spots on the back of the transmittor for a 12 volt 800mAh Ni-Cd pack (10 batteries). The Cyber Sky Parachute now inherently flys straight and true, and at an impressive range. ------------------------------------------------------------------------------