Great Planes Spirit Power Pod
10-09-2003, 06:30 AM
#2
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RE: Great Planes Spirit Power Pod
Can't say as I've tried one before, but I can comment on direct drive "550" motor systems in general. They work, but they're not the best option in most cases. To get much usable thrust from the motor, you have to prop it to draw lots of Amps. This means short run times and hot equipment, but still not a lot of thrust. Direct drive works best on small, sleek aircraft that are meant to fly fast, because the motor is turning something on the order of 20,000 RPM, spinning that little prop.
For a sailplane, you want plain old brute force. Lots of thrust, but not a lot of top-end speed. Geared 3:1 with a 12x8 folding propeller, that motor will have at least twice as much thrust for the same amount of input power. Only one problem... I don't think there's enough clearance for that on the power pod, either inside for the motor, or between the pod and the wing. Kinda counterproductive to be chopping your sailplane in half
For a sailplane, you want plain old brute force. Lots of thrust, but not a lot of top-end speed. Geared 3:1 with a 12x8 folding propeller, that motor will have at least twice as much thrust for the same amount of input power. Only one problem... I don't think there's enough clearance for that on the power pod, either inside for the motor, or between the pod and the wing. Kinda counterproductive to be chopping your sailplane in half
10-16-2003, 09:42 PM
#3
RE: Great Planes Spirit Power Pod
The 550 in the power pod should be adequate, but let me set your expectation. It is not going to take the plane straight up. You will have to circle the field as you fly to gain altitude. Nothing wrong with this, but you need to know what to expect.
I have the Great Planes power pod also. Mine came with a speed 601. Before I had a chance to put it on the plane I destroyed my Spirit in a winch accident. I am building a new one.
Use the right batteries
I did do some bench testing on the power pod with different battery combindations and have this advice. You must use a sub C size battery packs to get enough current to the motor. The 2/3A or 4/5A cells that you usually see in parkflyers can't put out enough current to run the motor at full power. I had to put two 7 cell 900 MAH 4/5A NIMH packs in parallel before I could get the motor to run at full speed. This is pushing those packs to about 13 amps per pack which is near their limit. So I bought some 7 cell SubC packs that are made for the Spectra which is the motorized version of the Spirit. It comes with a 550 motor. These can put out 20-25 amps which is what the power pod needs to run at full power. These do a good job of driving the motor at full power.
Balancing the plane
In order to keep the plane well balanced with the PowerPod, you need to put the battery on or very near the CG as it weighs about 13 ounces. If you put it away from the CG toward the rear of the plane you will have to add a lot of weight to rebalance the plane making it wildly heavy. As it is, with the power pod and battery on the plane, its weight will go from about 30 ounces to about 48 ounces. You don't want to have to add more lead to balance it.
I had a Spirit Select, the RTF Spirit package. It came with standard servos that were installed under the wing, which is the normal place. In the new Spirit I will use smaller servos, perhaps Hitec HS-81s and mount them in the bay in front of the wing. This will shift weight forward meaning that I will need less lead in the nose to balance the plane. It will reduce the weight of the plane by about 2.5-3 oz.
This will leave the area under the wing open so I can put the big battery pack there. With luck I can put it right on the CG and not have to rebalance the plane when I use the power pod thus avoiding any unnecessary weight and the hassell of rebalancing the plane constantly.
Hope this was helpful.
I have the Great Planes power pod also. Mine came with a speed 601. Before I had a chance to put it on the plane I destroyed my Spirit in a winch accident. I am building a new one.
Use the right batteries
I did do some bench testing on the power pod with different battery combindations and have this advice. You must use a sub C size battery packs to get enough current to the motor. The 2/3A or 4/5A cells that you usually see in parkflyers can't put out enough current to run the motor at full power. I had to put two 7 cell 900 MAH 4/5A NIMH packs in parallel before I could get the motor to run at full speed. This is pushing those packs to about 13 amps per pack which is near their limit. So I bought some 7 cell SubC packs that are made for the Spectra which is the motorized version of the Spirit. It comes with a 550 motor. These can put out 20-25 amps which is what the power pod needs to run at full power. These do a good job of driving the motor at full power.
Balancing the plane
In order to keep the plane well balanced with the PowerPod, you need to put the battery on or very near the CG as it weighs about 13 ounces. If you put it away from the CG toward the rear of the plane you will have to add a lot of weight to rebalance the plane making it wildly heavy. As it is, with the power pod and battery on the plane, its weight will go from about 30 ounces to about 48 ounces. You don't want to have to add more lead to balance it.
I had a Spirit Select, the RTF Spirit package. It came with standard servos that were installed under the wing, which is the normal place. In the new Spirit I will use smaller servos, perhaps Hitec HS-81s and mount them in the bay in front of the wing. This will shift weight forward meaning that I will need less lead in the nose to balance the plane. It will reduce the weight of the plane by about 2.5-3 oz.
This will leave the area under the wing open so I can put the big battery pack there. With luck I can put it right on the CG and not have to rebalance the plane when I use the power pod thus avoiding any unnecessary weight and the hassell of rebalancing the plane constantly.
Hope this was helpful.
10-16-2003, 10:05 PM
#4
RE: Great Planes Spirit Power Pod
This thread has a photo of moving servos way up front for improved balance and weight reduction
http://www.rcgroups.com/forums/showt...5&pagenumber=1
http://www.rcgroups.com/forums/showt...5&pagenumber=1
10-17-2003, 06:42 AM
#5
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RE: Great Planes Spirit Power Pod
Cool info.
FWIW, there are a few 4/5A cells out there now that will handle the kind of current your 550 motor needs. Two in particular are the Sanyo HR4/5AUP 1700mAh NiMH and the Sanyo HR4/5FAUP 1950mAh NiMH. A bit more expensive, but a LOT lighter than heavy Sub C cells. The "AUP" cell can handle up to 25 Amps, and the "FAUP" cell can handle up to 40. I use the FAUPs in a 37 Amp application, and they land only slightly warm. They're my favorites.
FWIW, there are a few 4/5A cells out there now that will handle the kind of current your 550 motor needs. Two in particular are the Sanyo HR4/5AUP 1700mAh NiMH and the Sanyo HR4/5FAUP 1950mAh NiMH. A bit more expensive, but a LOT lighter than heavy Sub C cells. The "AUP" cell can handle up to 25 Amps, and the "FAUP" cell can handle up to 40. I use the FAUPs in a 37 Amp application, and they land only slightly warm. They're my favorites.
