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Post by Dillzio on Apr 7, 2010 14:05:45 GMT 1
Hi gang,
I was wondering if it's possible to PROGRAM your radio to allow you to use a prop that's a little too big?
Say your motor is rated to 16a max, and you work out with your wattmeter that your motor is drawing 16a at 80% throttle, can you program the throttle range of the radio to only go up to 80%?
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Post by ginginho on Apr 7, 2010 16:05:35 GMT 1
You can adjust the throws of all the servos (inc throttle) on the Dx6i (+/- 125%), don't know about the HK radio though (which I think you are tempted with), I'd suspect so if it is a computer radio.
I had to do this to mine when I went B/L as it was WOT with the stick only half way up.
I'm not sure why you'd want to do what you describe though. It's very likely that the motor will be running very in-efficiently.
Just spec the motor and prop combo to suit the airframe and you are good to go. Alternatively, if you've got a motor that is over current with a certain prop, reduce the prop size. Simples. ;D
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Post by flydiver on Apr 7, 2010 16:26:51 GMT 1
Not a good idea. The ESC portion works by sending signals to the motor by switching on and off very fast. At full throttle it is sending signals full time. The FETs are doing minimal work pulling down voltage for the RX/servos. At 50% throttle the ESC is on half time, off half time. Overall voltage in the system is higher since the motor is working less hard and the FETs actually do more work pulling down the higher voltage. They'll run hotter at 50% throttle than full throttle.
It's also asking the motor to pull a prop it is not designed for. It's kind of like saying I'll put a governor on my car so I can pull a bigger trailer than it was designed for. It'll be out of it's efficiency range.
Best to prop down. If you look at efficiency graphs the best power/output is generally at about 75% of no-load RPM. But there is actually better efficiency with a smaller prop as long as you don't go so small you end up losing thrust.
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Post by Dillzio on Apr 8, 2010 0:00:17 GMT 1
I was hoping to maintain my current collection of props, but the 850kv motors seem to spin a bit too slow, and the 1100kv motors spins a bit too fast. I'm not sure it's really getting the motor to pull a prop it's not designed for, since at lower voltages that motor is designed to run a bigger prop anyway. I was just wondering if you could 'artificially' induce a lower voltage with the ESC.
EDIT:
I understand that the ESC would never be fully ON, so the FETs would never really get a rest, but if you had an overpowered motor you'd hardly be using WOT either, and that doesn't burn out the ESC.
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Post by flydiver on Apr 8, 2010 1:25:54 GMT 1
You have to adjust prop size when you change voltages a bunch. So 'designed' is a manner of describing it.
Go from a 7-cell to a 3S in the Cub and you really should down prop. This is true for any motor. The cheaper the motor likely the narrower the effective operating band.
You can use a low KV motor an go up in voltage or a higher KV motor and go down to get similar effect. The higher voltage will run lower amps all things being equal. But the battery and ESC will cost more. Always a balance.
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