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Old Jun 11, 2012, 01:49 AM
Grumpy old git.. Who me?
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Originally Posted by GetSome! View Post
Ken wrote 700kv on it
Yeah but it wouldnt be unreasonable to 'round up' a 683kv wind and call it 700 Most manufacturers state their motor kv as the nearest round number rather than the actual measured kv. Depending on how you measure kv you could easily be 20kv out in either direction anyway so picking the nearest round number is perfectly reasonable..

Steve
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Old Jun 11, 2012, 10:17 PM
VOLTS > AMPS
stgdz's Avatar
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Does 50% throttle result in 50% less amps? The fets are turning on and off faster when not at full throttle so there is more heat and heat usually equals amps.
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Old Jun 11, 2012, 11:52 PM
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Quote:
Originally Posted by JetPlaneFlyer View Post
Yeah but it wouldnt be unreasonable to 'round up' a 683kv wind and call it 700 Most manufacturers state their motor kv as the nearest round number rather than the actual measured kv. Depending on how you measure kv you could easily be 20kv out in either direction anyway so picking the nearest round number is perfectly reasonable..

Steve
It is possible, however unless there is mistake (like when he made me a 4315-480 that was more like 430. He rewound it free) Ken means what he writes on the motors.
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Old Jun 12, 2012, 12:10 AM
Grumpy old git.. Who me?
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Quote:
Originally Posted by -= GYRO =- View Post
It is possible, however unless there is mistake (like when he made me a 4315-480 that was more like 430. He rewound it free) Ken means what he writes on the motors.
A difference of approx 50 is 'doable'. It's when people expect Ken to be able to wind precisely any kv number of their choosing down to the single digit accuracy that they are deluding themselves.
I fully appreciate that Ken is an expert motor winder but he's still bound by the laws of physics and a turn of wire is still a turn of wire. No matter how good you are you cant wind half a turn

If in doubt about it just drop Ken a line and I'm sure he'll confirm what I'm saying.

Steve
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Old Jun 12, 2012, 12:35 AM
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For the record he had no problem hitting my 1130kv mark I requested. I don't see not being able to go somewhere in between 683 and 750 kv also.
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Old Jun 12, 2012, 02:22 AM
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Originally Posted by JetPlaneFlyer View Post
A difference of approx 50 is 'doable'. It's when people expect Ken to be able to wind precisely any kv number of their choosing down to the single digit accuracy that they are deluding themselves.
I fully appreciate that Ken is an expert motor winder but he's still bound by the laws of physics and a turn of wire is still a turn of wire. No matter how good you are you cant wind half a turn

If in doubt about it just drop Ken a line and I'm sure he'll confirm what I'm saying.

Steve
I'm sorry Steve, but I'm not sure what your point is?
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Old Jun 12, 2012, 05:11 AM
Grumpy old git.. Who me?
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Quote:
Originally Posted by -= GYRO =- View Post
I'm sorry Steve, but I'm not sure what your point is?
The only point was that it's impossible even for someone as expert as Ken to wind every specific kv imaginable in incremental steps of anything close to 1kv (as some seem to think is possible).
When winding a motor kv is adjusted by varying the number of turns of wire that you wrap around the stator 'teeth', more turns = lower kv. Each turn makes a difference of many kv (perhaps 50 or so for a motor like the DM2820) so it's impossible to hit any specific kv between what the number of turns produces.

For the DM2820 the achievable kv (in delta configuration) seems to be: 966, 750, 683, 638, and 600 (some of these numbers are probably rounded slightly). Most of these steps will represent one turn of wire on the stator, though the jump between 750kv and 966kv is probably three turns meaning kv's of approx 810 and 880 could also be wound.
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Old Jun 12, 2012, 06:48 AM
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I reckon the DM2820 as a 880 would rock on 3s for smaller lighter planes swinging 14x7 props. Sort of like the Scorpion 3020-890, but a few less amps in that kV range.
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Old Jun 12, 2012, 07:51 AM
Not as Good as The Kid
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Originally Posted by stgdz View Post
Does 50% throttle result in 50% less amps? The fets are turning on and off faster when not at full throttle so there is more heat and heat usually equals amps.
No. I guess it may be possible to set the throttle curve to do so, but we have data from the original tests that shows some half-throttle setting readings along with WOT to get a better understanding of this. You will see that on average, 50% throttle was 70% of the WOT RPMs, 27% of the WOT Amps, and 27% of the WOT Watts.

This means that more than 70% of the power and consumption of energy comes in the last 30% of the prop speed. There is a lot more going on at the top end that will compensate for the resistance of switching at the lower settings. The increase in current will geometrically increase the relationship between resistance and heat.
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Old Jun 12, 2012, 08:16 AM
VOLTS > AMPS
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Originally Posted by Aeroplayin View Post
No. I guess it may be possible to set the throttle curve to do so, but we have data from the original tests that shows some half-throttle setting readings along with WOT to get a better understanding of this. You will see that on average, 50% throttle was 70% of the WOT RPMs, 27% of the WOT Amps, and 27% of the WOT Watts.

This means that more than 70% of the power and consumption of energy comes in the last 30% of the prop speed. There is a lot more going on at the top end that will compensate for the resistance of switching at the lower settings. The increase in current will geometrically increase the relationship between resistance and heat.
ok I found franks data, I knew the data was on the webpage somewhere but I think it was somewhat late when I posted the question. Looks like amps rise logarithmically.

I always wondered how you guys could get such long flight times at half throttle when I usually zip around at 3/4-full throttle and seemingly come down with the same flight time. Guess thats why I like my setup as my flight times are now longer than the old 12x6 setups
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Old Jun 12, 2012, 09:05 AM
Not as Good as The Kid
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Originally Posted by stgdz View Post
ok I found franks data, I knew the data was on the webpage somewhere but I think it was somewhat late when I posted the question. Looks like amps rise logarithmically.

I always wondered how you guys could get such long flight times at half throttle when I usually zip around at 3/4-full throttle and seemingly come down with the same flight time. Guess thats why I like my setup as my flight times are now longer than the old 12x6 setups
It also looks like Lee's data showed about the same results plus or minus a tick or two.

For me, the high speed stuff is not what I'm looking for because I have planes that can do over 110 mph when I feel the need for speed, but with the 48 Edge, I'm averaging about 250mAh per minute.

This means my average current draw is 26A, which is 400W. This also means 70% of WOT Amps and Watts, so as far as stick settings, I'm right in the half-throttle range, according to the average test data percentages.
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Old Jun 12, 2012, 09:23 AM
Grumpy old git.. Who me?
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I dropped Ken an email to confirm what kv's he can wind and what he can't. He confirmed he could do those I listed above but also using different winding method he can also do a step inbetween those I stated, though he said that it gets difficult.

Depending on the motor he says he can typically achieve 20kv increments, but some arent easy.

Steve
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Old Jun 12, 2012, 09:25 AM
Grumpy old git.. Who me?
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Anyone have any experience of using the DM3615-750 in a 48" EXP?

Ken gave me details of this motor and in it's light weight version it's only a few grams heavier than th DM2820 and a little shorter. Seems like this might be the ideal motor to spin a 14" prop on the 48" EXP's and not have to compromise on speed or be worried about structural; strangth of the motor?

Steve
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Old Jun 12, 2012, 09:44 AM
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Quote:
Originally Posted by JetPlaneFlyer View Post
I dropped Ken an email to confirm what kv's he can wind and what he can't. He confirmed he could do those I listed above but also using different winding method he can also do a step inbetween those I stated, though he said that it gets difficult.

Depending on the motor he says he can typically achieve 20kv increments, but some arent easy.

Steve
yep, just peeked thru my cowling to see what ken wrote on the 2820...702kv
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Old Jun 12, 2012, 12:33 PM
Team Hillbilly (UK)
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United Kingdom, England, Cambs
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I am curious why it's not possible to hand wind to within 1% ? I know you can with a semi-automatic process.....as the +/- 1% was a tolerance - ok there was more rigging/tensioners wire feeders and guides...etc... but should be able to do some of this within a hand wired process no?
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