7LikesG-Force Motor Checker
11-26-2014, 04:10 AM
#47
I just picked up one of these units. It's the one the reads to 50*. I have decided that I will make readings at 40 and 45 as well as 50, and if I have to, I can estimate 55 and 60. Sure it would be nice to actually see it, but I will manage.
Everything I race is 1s, so the voltage tested at is double. It won't run on 4.2v. Again, I will manage. EA: do you think the KV and Amps are linear to the voltage input? Or do KV and amps follow a different curve in relation to voltage? Its all relative, just curious.
Everything I race is 1s, so the voltage tested at is double. It won't run on 4.2v. Again, I will manage. EA: do you think the KV and Amps are linear to the voltage input? Or do KV and amps follow a different curve in relation to voltage? Its all relative, just curious.
I hope EA doesn't mind me chiming in here!
Extrapolating kV and current draw past 50 degrees is a challenge. The results are very non-linear; everything really skyrockets at higher timing settings. I don't know what the curve is, but maybe someone here can give us the closest mathematical approximation to it (total guess: tangent?).
kV does not change with voltage. Half the voltage will give you half the RPM, which is the same kV.
Strangely enough, free-running amp draw also doesn't change much with voltage. Frictional and hysteresis losses are approximately linear with RPM, so 1/2 voltage will give about 1/2 the power loss. Since the voltage has already been halved, the current will remain the same to give 1/2 the power loss.
11-26-2014, 02:13 PM
#49
Hi Brian,
I hope EA doesn't mind me chiming in here!
Extrapolating kV and current draw past 50 degrees is a challenge. The results are very non-linear; everything really skyrockets at higher timing settings. I don't know what the curve is, but maybe someone here can give us the closest mathematical approximation to it (total guess: tangent?).
kV does not change with voltage. Half the voltage will give you half the RPM, which is the same kV.
Strangely enough, free-running amp draw also doesn't change much with voltage. Frictional and hysteresis losses are approximately linear with RPM, so 1/2 voltage will give about 1/2 the power loss. Since the voltage has already been halved, the current will remain the same to give 1/2 the power loss.
I hope EA doesn't mind me chiming in here!
Extrapolating kV and current draw past 50 degrees is a challenge. The results are very non-linear; everything really skyrockets at higher timing settings. I don't know what the curve is, but maybe someone here can give us the closest mathematical approximation to it (total guess: tangent?).
kV does not change with voltage. Half the voltage will give you half the RPM, which is the same kV.
Strangely enough, free-running amp draw also doesn't change much with voltage. Frictional and hysteresis losses are approximately linear with RPM, so 1/2 voltage will give about 1/2 the power loss. Since the voltage has already been halved, the current will remain the same to give 1/2 the power loss.
Your information never bothers me at all! You have more knowledge about this type of stuff than just about anyone in RC so your input is always welcome! Thanks!
EA
11-27-2014, 09:47 AM
#50
Hello,
Does anyone have an idea what the maximum current draw of a 13.5 with no load at max rpm and timing would be?
Thanks Michael
Does anyone have an idea what the maximum current draw of a 13.5 with no load at max rpm and timing would be?
Thanks Michael
11-28-2014, 10:55 AM
#51
Ah, I feel like I am getting my "geek" on with this tool. I've already filled up several sheets of paper with recordings and formulas. Howard, thanks for response with big words! 
I wanted to test that answer with some data on my end and wondered how I could do that. The VX1 records max rpm. Not real convenient to do, but I did it. Took 3 samples at 4.1 volts. Put an Amp meter inline on the battery. And you are absolutely correct, that amperage is relatively unchanged from 4.2 to 8.4. From my residential wiring days and the classroom training, they taught us that as voltage increases, amperage decreases if the load is fixed. Its the reason that heat or hot water run off of 240v as it will operate more efficiently and on smaller gauge wire. Apparently this doesn't carry over to brushless motor operation.
So I had a motor display 2783 KV on the GForce @ 8.3v. If I were to correct that for 4.2v, I would multiply the KV by 1S voltage, you get 11688 free spin rpm.
From the VX1, I get 9730 max rpm on that same motor. So divide max rpm by pack voltage (4.1v) and I get 2373KV.
The amperage is the same from the GForce at 8.3v and the from the amp meter at 4.1v
So there is a slight difference in KV rating. Of course where I am going with this is to see if I can go from motor A to motor B with a little calculation and come up with identical performance on the track. I know that won't happen, but its worth a shot.
I'd like to see a power or a hp #. Just because you see a big KV # doesn't mean the motor makes more power. Wattage (volt x amps) is not going to reveal anything useful, is it?
So far, I've been able to identify a bum bearing and see the results improve. I've played with rotor to sensor shimming and witnessed the changes. I guess my goal would be: gather some data, calculate that this motor with this timing with this gear should be optimal. I'm open to any suggestions at this time.
I'll take my pocket protector off now.
I wanted to test that answer with some data on my end and wondered how I could do that. The VX1 records max rpm. Not real convenient to do, but I did it. Took 3 samples at 4.1 volts. Put an Amp meter inline on the battery. And you are absolutely correct, that amperage is relatively unchanged from 4.2 to 8.4. From my residential wiring days and the classroom training, they taught us that as voltage increases, amperage decreases if the load is fixed. Its the reason that heat or hot water run off of 240v as it will operate more efficiently and on smaller gauge wire. Apparently this doesn't carry over to brushless motor operation. So I had a motor display 2783 KV on the GForce @ 8.3v. If I were to correct that for 4.2v, I would multiply the KV by 1S voltage, you get 11688 free spin rpm.
From the VX1, I get 9730 max rpm on that same motor. So divide max rpm by pack voltage (4.1v) and I get 2373KV.
The amperage is the same from the GForce at 8.3v and the from the amp meter at 4.1v
So there is a slight difference in KV rating. Of course where I am going with this is to see if I can go from motor A to motor B with a little calculation and come up with identical performance on the track. I know that won't happen, but its worth a shot.
I'd like to see a power or a hp #. Just because you see a big KV # doesn't mean the motor makes more power. Wattage (volt x amps) is not going to reveal anything useful, is it?
So far, I've been able to identify a bum bearing and see the results improve. I've played with rotor to sensor shimming and witnessed the changes. I guess my goal would be: gather some data, calculate that this motor with this timing with this gear should be optimal. I'm open to any suggestions at this time.
I'll take my pocket protector off now.
11-28-2014, 12:44 PM
#53
Ah, I feel like I am getting my "geek" on with this tool. I've already filled up several sheets of paper with recordings and formulas. Howard, thanks for response with big words! I wanted to test that answer with some data on my end and wondered how I could do that. The VX1 records max rpm. Not real convenient to do, but I did it. Took 3 samples at 4.1 volts. Put an Amp meter inline on the battery. And you are absolutely correct, that amperage is relatively unchanged from 4.2 to 8.4. From my residential wiring days and the classroom training, they taught us that as voltage increases, amperage decreases if the load is fixed. Its the reason that heat or hot water run off of 240v as it will operate more efficiently and on smaller gauge wire. Apparently this doesn't carry over to brushless motor operation.
So I had a motor display 2783 KV on the GForce @ 8.3v. If I were to correct that for 4.2v, I would multiply the KV by 1S voltage, you get 11688 free spin rpm.
From the VX1, I get 9730 max rpm on that same motor. So divide max rpm by pack voltage (4.1v) and I get 2373KV.
The amperage is the same from the GForce at 8.3v and the from the amp meter at 4.1v
So there is a slight difference in KV rating. Of course where I am going with this is to see if I can go from motor A to motor B with a little calculation and come up with identical performance on the track. I know that won't happen, but its worth a shot.
I'd like to see a power or a hp #. Just because you see a big KV # doesn't mean the motor makes more power. Wattage (volt x amps) is not going to reveal anything useful, is it?
So far, I've been able to identify a bum bearing and see the results improve. I've played with rotor to sensor shimming and witnessed the changes. I guess my goal would be: gather some data, calculate that this motor with this timing with this gear should be optimal. I'm open to any suggestions at this time.
I'll take my pocket protector off now.
I wanted to test that answer with some data on my end and wondered how I could do that. The VX1 records max rpm. Not real convenient to do, but I did it. Took 3 samples at 4.1 volts. Put an Amp meter inline on the battery. And you are absolutely correct, that amperage is relatively unchanged from 4.2 to 8.4. From my residential wiring days and the classroom training, they taught us that as voltage increases, amperage decreases if the load is fixed. Its the reason that heat or hot water run off of 240v as it will operate more efficiently and on smaller gauge wire. Apparently this doesn't carry over to brushless motor operation. So I had a motor display 2783 KV on the GForce @ 8.3v. If I were to correct that for 4.2v, I would multiply the KV by 1S voltage, you get 11688 free spin rpm.
From the VX1, I get 9730 max rpm on that same motor. So divide max rpm by pack voltage (4.1v) and I get 2373KV.
The amperage is the same from the GForce at 8.3v and the from the amp meter at 4.1v
So there is a slight difference in KV rating. Of course where I am going with this is to see if I can go from motor A to motor B with a little calculation and come up with identical performance on the track. I know that won't happen, but its worth a shot.
I'd like to see a power or a hp #. Just because you see a big KV # doesn't mean the motor makes more power. Wattage (volt x amps) is not going to reveal anything useful, is it?
So far, I've been able to identify a bum bearing and see the results improve. I've played with rotor to sensor shimming and witnessed the changes. I guess my goal would be: gather some data, calculate that this motor with this timing with this gear should be optimal. I'm open to any suggestions at this time.
I'll take my pocket protector off now.
It sounds like something is just not right with the motor checker when running at low voltage. (EDIT: no, see below) For comparison, I just ran a ThunderPower 17.5 (timing=38 indicated) from 1s and 2s batteries. The ESC was a Novak Edge, using a Novak Smart Boost as the regulator on 1s, and the internal regulator on 2s. Here's my data:
Voltage RPM Calculated kV
3.815 9930 2603
7.57 19410 2564
As you can see, the kV was virtually unchanged: about 1.5% different, most of which I would attribute to the voltmeter accuracy. Your numbers vary by 17%, which is a little more than I would expect. But I'm not sure how accurate your voltage measurements are.
You are right, measuring power consumption at no load is of very limited value.
EDIT: Duh, silly me, the motor checker runs in sensorless mode, and you were using a VX1 for 1s testing, which I'm guessing was running in sensored mode. That explains the difference in kV. You'd get the same kV if you set the motor timing to zero.
Last edited by howardcano; 11-28-2014 at 01:19 PM.
11-28-2014, 01:26 PM
#54
I did a quickie check of your current data. It has a reasonable fit to my guess of a tangent up to 45 degrees
, but no higher.
Last edited by howardcano; 11-28-2014 at 01:45 PM.
11-28-2014, 06:50 PM
#55
Hey guys, I've long wondered what effect rotor shimming has on overall power. I realize that this thread is for the motor checker, but this thread clearly has a higher collective IQ than the majority of other threads, and I would like to capitalize on this. I've always just pulled the necessary shims to allow the rotor to find its own electrified center. Is this wrong? Any info is appreciated!
11-28-2014, 10:36 PM
#56
All I can say at this point, nothing seems to be consistent. I went through a pile of 13.5's today. I would make some recordings to baseline, then make some alterations and retest. Some improve, some not and I am not even sure that I am seeing different numbers as a reduction. At this time, I am just fooling around and making numbers. I don't know if I am making good numbers, bad numbers or just different numbers. Until I can come up with a solid load test, I won't know if I am making forward progress. I can pop in a 12.3 rotor and get a higher KV rating then a 12.5 rotor. But I know that 12.5 will let me pull another tooth and be faster at the end. Yes, a 12.3 rotor should produce a higher KV, but is it making more power? Some motors I have magnetically centered the rotor and then moved the sensor board closer. Some improve, some don't. I have not come up with a cookie cutter formula for building motors. So Big Al, sorry buddy. I don't have that answer.
At least not yet.
At least not yet.
11-29-2014, 01:39 AM
#57
can choice SKYRC with bester price
11-29-2014, 07:26 AM
#58
Tech Master
iTrader: (19)
All I can say at this point, nothing seems to be consistent. I went through a pile of 13.5's today. I would make some recordings to baseline, then make some alterations and retest. Some improve, some not and I am not even sure that I am seeing different numbers as a reduction. At this time, I am just fooling around and making numbers. I don't know if I am making good numbers, bad numbers or just different numbers. Until I can come up with a solid load test, I won't know if I am making forward progress. I can pop in a 12.3 rotor and get a higher KV rating then a 12.5 rotor. But I know that 12.5 will let me pull another tooth and be faster at the end. Yes, a 12.3 rotor should produce a higher KV, but is it making more power? Some motors I have magnetically centered the rotor and then moved the sensor board closer. Some improve, some don't. I have not come up with a cookie cutter formula for building motors. So Big Al, sorry buddy. I don't have that answer.
At least not yet.
At least not yet.
As always, YMMV.
11-29-2014, 04:28 PM
#59
All I can say at this point, nothing seems to be consistent. I went through a pile of 13.5's today. I would make some recordings to baseline, then make some alterations and retest. Some improve, some not and I am not even sure that I am seeing different numbers as a reduction. At this time, I am just fooling around and making numbers. I don't know if I am making good numbers, bad numbers or just different numbers. Until I can come up with a solid load test, I won't know if I am making forward progress. I can pop in a 12.3 rotor and get a higher KV rating then a 12.5 rotor. But I know that 12.5 will let me pull another tooth and be faster at the end. Yes, a 12.3 rotor should produce a higher KV, but is it making more power? Some motors I have magnetically centered the rotor and then moved the sensor board closer. Some improve, some don't. I have not come up with a cookie cutter formula for building motors. So Big Al, sorry buddy. I don't have that answer.
At least not yet.
At least not yet.
I'll eventually make it to the community center, too many packages to deliver this time of year!
12-03-2014, 05:12 AM
#60
Tech Adept
Ciao AE,
i sent you a pm
Max
i sent you a pm
Max
Last edited by mtaddei; 12-03-2014 at 06:46 AM.