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A Nacked Axe
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Last edited by flatiron; Mar 22, 2007 at 02:15 AM.
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Heat Sink compound
Thanks for the replies about heat sink compound. I did a google search on the Arctic Silver brand and it led me to some interesting tests that have been run to see how well various types of compound perform. My conclusion is that it will definitely help transfer heat from the motor to the heat sink, but can be a bit messy to use. Different brands have different degrees of messiness. Anyway, I intend to use it to give the motor whatever extra life I can. I notice the motor on the Axe came with compound on it.
Also, it's good that some have noticed the poor way the standard Axe CP heat sink is installed by the factory. Looks like they just used a heat sink that was readily available to them, but which doesn't fit well due to the frame being too narrow at the top. It doesn't slide up all the way to the top of the motor, which means it covers over the large cooling slots that are on the motor. The motor does have it's own cooling fan built in, which is easy to see when you pull off the heat sink and look in the slots. But, the heat sink as sent out by the factory defeats the cooling fan. This is an important item to correct, in my opinion, if you don't want to seriously overheat the motor, and reduce the useful life of it. I see different approaches to modifying the heat sink to expose the cooling slots in the motor. I have elected to modify the heat sink so that I can push it all the way up to the top of the motor, which is the hottest end. There are no magnetic windings below the cooling slot. The motor core is all above that, so I figure it may be best to push the heat sink all the way up and fully expose the cooling slots instead of just exposing them 2/3 or 3/4 of what was designed into them by the engineer. Bud |
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The choice of brushed ESCs for tail could be tricky. Heli guide v.17 @swashplate.co.uk warns against cheap GWS controllers. They claim entry-level ones have only 16 throttle steps--insufficient for robust tail control. This is the reason I am considering ESC with 1024-step throttle . Currently, I am still waiting for Tower shipment with blade grips/HS55s. I intend to install them, try to fly my AxeCP and then move on with BL/HH gyro conversion. |
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Heat Sink modificationQuote:
After modifying the fins to allow the sink to move all the way up, it will still cover the tops of the motor cooling slots a tiny bit. The full width of the slots will be exposed, but the top 20% or so will still be covered. I used the Dremel to remove the little bit of heat sink that was still covering part of the cooling slots on each side so that they are now fully exposed. I also picked up some heat sink compound from Radio Shack for $2.99 which I will use to further help the heat transfer from the motor to the heat sink. I think these mods will deliver a noticeable decrease in motor temperature. Bud |
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Motor choiceQuote:
Let me illustrate my motor selection based on your numbers. Word of caution: I only have fixed-wing RC experience (flying ‘lectrics since 2001); I am totally n00b heli-wise. Ok, so you measured 9.92V/11Amps running full throttle, about 109W. Assuming properly broken-in motor, that translates to about 55W of mechanical power at the pinion (brushed motors have roughly 50% efficiency). If you maintain the same heli weight after BL conversion (lighter motor, no 3-in-1, BUT added weight of HH gyro), you will need the same 55W from motor. BL motors are more efficient (about 80%), so you’ll need less current from battery. At 80% efficiency, BL motor should draw about 69W of electric power. Assuming that 3s LiPo sags to 10V under load, that translates to roughly 7amps of current. This is exactly what I want to achieve from BL conversion—current draw from battery should decrease from 11 amps to 7 amps (longer flight time). Now going back to our motor selection: we need BL motor designed to operate around 7amps with 3s battery to have the same performance and longer flight time. That means 70W motor, definitely NOT a 150+Watt monster--surprise! My original 100W selection is probably overkill based on your data; I need to consider something lighter, like this 40g BL motor. Considering stock motor weighs over 100g, this motor can provide flight time increase just by lowering the heli's all-up weight Hey, PROs, any suggestions? Thanks! |
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Axe CP as a beginner heli?
For those of you who have already purchased a Axe CP, would you purchase it again as a beginners helicopter? If not, what would you choose?
Not trying to create a debate here. I am looking at an Axe CP and I am wondering if I am getting in over my head. No heli experience, so please be gentle. |
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If your LHS doesn't stock the Lama I believe it can use the Blade CX2 main rotors. |
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1) Get tower shipment with blade grips/HS55s & install them (ordered 3/20, estimated arrival date: between 03/28/07 - 04/02/07) 2) Fly my AxeCP with new servos and confirm it is now controllable 3) Order HH gyro, ESC, motor, and a bunch of other components for BL conversion 4) Rip out 3-in-1 and stock main rotor motor 5) Install BL motor 6) Install HH gyro, 2 ESCs, route the wires 7) Enjoy my new AxeCP Of course I would like to get it done without drilling new holes in the frame. However, since items (4) and (6) are very close to "total teardown and rebuild" anyway, I don't mind tweaking the motor mount for BL install. The biggest question that I have is why my fixed-wing electric power design experience contradicts your findings. You have 150+ watt motor running happily, right? Am I missing something or you just run your BL monster at less than half of its rated power? I might be totally of in my power estimates. I'd like to figure that out before I order the motor and drill new holes in the frame ;-) |
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I agree with everything Jman424 said, but you have to ask yourself one question. Do I want to fly outside. Coax's and most FP's don't do well in the outdoors. They don't have enough thrust to overcome wind. I can't tell you what a good first heli would be for you. It's different for different people. Some start with coaxial helis, some with FP's, and some with CP's. It's a fact CP heli's do have more parts and generally more power which makes the learning curve steeper. However my recommendation is instead of getting a coax and then moving on to a CP I'd get a good sim and learn how to fly it there then go straight to a CP. Just my .02 |
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If this is true then at a 50% efficiency the motor would draw 164 watts for 109 watts of work. I'm also confused at the meaning of this statement. "that translates to about 55W of mechanical power at the pinion". How would that effect wattage? Also how did you get 69 watts? OK, I do know this. Your numbers are very useful. If the OE main motor is pulling 109 watts at full throttle with a 50% eff. rating then a brushless with an 80 % eff. rating will only pull 77 watts for the same amount of work. If that's at the same 9.92 volts then the amps drop to 7.7 amps. That's a plus. Once I get everything installed I think I'll have a much better idea of how to guage brushed and BL motors. AHHHH... I have a headache |
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The Return of Stable Hovers!
Yaaay! Made more progress today, but also found new issues to iron out.
I flew out a pack today in sliding and hopping, then went into some brief low level hovers. The head is lookin pretty good - nice traking again! Got some nice, glass-like hovers in. The tail is smooth enough, BUT - - - - I backed off on the TR Trim pot setting, and set Gyro Gain to almost minimum. I then did a re-binding with the DX6 and AR6000. Even with max right rudder trim ( = 40 ) I still have to apply right rudder stick to keep her straight. DArn! I would prefer to NOT have to increase that TR Trim pot setting... That's the biggest issue but there is another - I'll detail in the next post because its signfigant and I need some opinions... |
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