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  #21  
Old 08-14-2019, 10:27 AM
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Thanks, many more good points

So, I guess the question should have been:
...in your opinion, which method would be best, for us here on the forum, to use?
(with the tools/instruments we have available)

Just use whole numbers (like 53V)
...rounded down (from 53.4V)

Is the VPR (volts per revolution) data even important or helpful to us? (in our situation)
...I just kinda threw it in

Is this "unloaded" data that I've gathered of any use to us?
...I understand that we would need "loaded" data for doing any type of speed calculations.

* Yes, I (& maybe others) would be very interested in a "data logger"
...if you have time, a detailed thread on concept, materials, construction & use would be very much appreciated.
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Old 08-14-2019, 05:42 PM
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rev per volt under load is dependend on the load itself.
120 lbs rider at 7:1 and 300 lbs rider @ 5:1 makes a whole lot of a different load
So no in the end it's just some arbitrary number..
If you however intend to do that for all of your PMDCs
(BLDC are a different bred and cannot be measured that way)
it'd allow us to compare two "different" motors under reasonably identical loads

So yeah keep on.

BUT: as I said the only real use of such is to have the voltage read at the very instant the load is applied..
slightly before or after is basically adding another variant (the batpack, charge density, self recovery rate, capacity etc..)
That's why lab testing is usually done with fixed voltage and current power sources and
of course fixed loads.

Nevermind...

I have a variable voltage divider in mind, I just have to see if it's cheaper to have it self-adjusting (i.e. by a chip) or manually adjusting (i.e. by a poti)
it'll need to get clipped for a decent resolution of course, but I think I can do that quite cheaply.
the rest is a simple arduino (chinese clone for a dollar will do) and the inductive pickup you have up there..
Oh no.. an SD card module for data storage
I'll make the parts list as I go, but I think it'll have a low partscount and low costs in the end...
we'll see.

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Old 08-14-2019, 11:28 PM
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Kool!

Keepin' on, I did RPM tests on each of the motors on the !Arriba! kart
…& got some interesting results

The top speed of the left motor (running counter-clockwise) seemed to be 3,528 RPM's
...but, the top speed of the right motor (running clockwise) seemed to be 3,801 RPM's

*Would this indicate that these motors operate "more efficiently" when running clockwise?

Here is a video of the tests

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Old 08-15-2019, 05:17 AM
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Quote:
Originally Posted by Functional Artist View Post
…& got some interesting results

The top speed of the left motor (running counter-clockwise) seemed to be 3,528 RPM's
...but, the top speed of the right motor (running clockwise) seemed to be 3,801 RPM's

*Would this indicate that these motors operate "more efficiently" when running clockwise?
the commutators are slightly biased on almost all PMDC motors,
I thought you're aware of that.

Most diagrams are even split for CW and CCW rotation.

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Old 08-15-2019, 06:38 AM
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Quote:
Originally Posted by itsid View Post
the commutators are slightly biased on almost all PMDC motors,
I thought you're aware of that.

Most diagrams are even split for CW and CCW rotation.

'sid
Nope, I guess not
...(if you would) please explain further

But, during my research, I've read that the brushes in (some) motors are mounted at an angle
...so, running them backwards, as opposed to the "originally" designed direction, effects the performance/efficiency
(& for some, may not even be recommended)

Still learnin' on motor performance charts (diagrams)
...but, I don't remember us discussing CW vs. CCW rotation
...or even seeing anything about it on any of the charts

http://www.diygokarts.com/vb/showthread.php?t=41428

* Could this, CW vs. CCW RPM difference, be why the !Arriba! kart unexpectedly turned to the left
...& flipped on me last summer?

If both throttles were operated "in sync"
...the right motor would "rotate", the right tire, a bit faster than the left
...causing an abrupt left turn, when the front wheels "lifted" & lost their "directional" traction
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Old 08-15-2019, 12:03 PM
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Hm.. I thought we scratched that sometime...
Nevermind

I'll try to keep it simple...

The commutator bar (what the brushes run on)
switches the coils on the rotor so that the "upcoming" coil pulls itself closer to the next magnet

In order for the "currently active" coil not to cause too much of a counteracting force,
it is ideally switched off already;
that unfortunately is impossible with a brushed motor
instead both coils are actually active at the transition of the brush from one coil to the next.

That transition is made such that the upcoming coil has an advantage over the currently active one, in order to get at least close to a perfect motor.

that is easiest by either angling the brushes slightly or -which I think is more common-
offset them slightly (not inline with the rotor axle)
That's the bias I mentioned earlier..
the brushes prefere the 'upcoming' coil over the active one.
So the upcoming coil is pulling harder forward than the active one is trying to stay where it is (under it's magnet)

And it's perfectly normal that when you run such biased motor in reverse it does the exact opposite
(it prefers the active coil over the upcoming one)
thus the motor has a lower efficiency
since it's slowed down by the currently activated coil (trying to stick to the magnet it sits under) before the upcoming coil can fully take over and pull forward

And no, that can NOT flip a kart!
the difference under load is nowhere near a noteworthy amount.
it should be self aligning thanks to road/wheel friction alone

A small pebble under a front wheel can cause way more of an upset steering momentum

And no you misunderstood that whole rpm/volt thing anyways..
it's not a linear ratio anyways.

at 1V the motor might not turn at all, spin 2000 rpm at 15V at maxes out at 36V with 3600 rpm
Now what rpm/volt would you now label the motor?
And the more load you apply the more you slow the motor down (at a constant voltage)
the 48V 1kW my1020 PMDC runs with no load 3600rpm and 3000rpm under peak loads all at
a perfect 48V for example

All you do is adding hints and indicators, none is actually of 'scientific value'
So don't try too hard

'sid
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  #27  
Old 08-15-2019, 03:10 PM
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Quote:
Originally Posted by itsid View Post
Hm.. I thought we scratched that sometime...
Nevermind

I'll try to keep it simple...

The commutator bar (what the brushes run on)
switches the coils on the rotor so that the "upcoming" coil pulls itself closer to the next magnet

In order for the "currently active" coil not to cause too much of a counteracting force,
it is ideally switched off already;
that unfortunately is impossible with a brushed motor
instead both coils are actually active at the transition of the brush from one coil to the next.

That transition is made such that the upcoming coil has an advantage over the currently active one, in order to get at least close to a perfect motor.

that is easiest by either angling the brushes slightly or -which I think is more common-
offset them slightly (not inline with the rotor axle)
That's the bias I mentioned earlier..
the brushes prefere the 'upcoming' coil over the active one.
So the upcoming coil is pulling harder forward than the active one is trying to stay where it is (under it's magnet)

And it's perfectly normal that when you run such biased motor in reverse it does the exact opposite
(it prefers the active coil over the upcoming one)
thus the motor has a lower efficiency
since it's slowed down by the currently activated coil (trying to stick to the magnet it sits under) before the upcoming coil can fully take over and pull forward

And no, that can NOT flip a kart!
the difference under load is nowhere near a noteworthy amount.
it should be self aligning thanks to road/wheel friction alone

A small pebble under a front wheel can cause way more of an upset steering momentum

And no you misunderstood that whole rpm/volt thing anyways..
it's not a linear ratio anyways.

at 1V the motor might not turn at all, spin 2000 rpm at 15V at maxes out at 36V with 3600 rpm
Now what rpm/volt would you now label the motor?
And the more load you apply the more you slow the motor down (at a constant voltage)
the 48V 1kW my1020 PMDC runs with no load 3600rpm and 3000rpm under peak loads all at
a perfect 48V for example

All you do is adding hints and indicators, none is actually of 'scientific value'
So don't try too hard

'sid
Thanks, for another great explanation

I'm just explorin' & playin' with my "new toy"

The Manta motor (on El Moto) listed 72 RPV on the spec sheet

So, I guess, I was using that figure, as a base
...& figurin' the RPV ratio of these little motors
(to use as kinda like an efficiency indicator)
...but, mainly just for comparison purposes

Speakin' of El Moto, I did an (unloaded) RPM test on 'er too



The meter showed 545 RPM's at the rear axle (fully charged @ 49.5V)
…& if we multiply that figure by the gear ratio (5.4:1)
we get 2,943 RPM's (545 x 5.4 = 2,943)

But, remember the spec sheet "listed" (72 RPV's)
…so, if we multiply the inputted Voltage of (49.5V) by the "listed' RPV
...we should have gotten 3,564 RPM's (545 x 72 = 3,564)

* Maybe the Kelly controller is factory programmed to NOT run @ 100% initially?
...until adjusted by end user?
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  #28  
Old 08-15-2019, 08:16 PM
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Don't gt me started again on what I think about "Manta" ...
I mean I don't need to remind you about what they suggested you to controll the motor with, do I?
So their claim of 72 RPV is taken with an ounce of salt (or say the heaviest grain you find )

There is no such thing as RPV on any motor really..
not on brushed and not on brushless motors..
it's an indicator value
(a value you might expect under controlled ideal circumstances; however those might need to look like; AT BEST)
at worst it's a blunt lie (I mean Manta motors... *cough*)

I think we've come to the conclusion yours is at least a sibling to the Motenergy ME0709, right?

So, let's go with that well documented "non fictionally improved" motor
as a comparision, shall we?

it runs slightly slower (2400 rpm'ish in both directions at a fixed 48V) completely unloaded
so in theory 50 RPV

btw at 24V it runs 1150 RPM unloaded ~ 47 RPV
and at 36V it runs 1700 RPM unloaded ~ 47 RPV

it itself maxes out at about 4.5k rpm at 72Volts as far as I know
So in theory 62 RPV (cannot find the diagram for a 72V setup atm)

And there you go... different volts yield different RPVs on the exact same motor

Talking of it..
see:
CLOCKWISE
Click image for larger version

Name:	me0709_48V_CW.jpg
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and COUNTER CLOCKWISE
Click image for larger version

Name:	me0709_48V_CCW.jpg
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ID:	110911
diagrams
And the ripples (most apeparant in the efficiency curve)
tell you it preferes clockwise rotation,
drawing less amps and running smoother..
BUT the difference in rotational speed is not noteworthy

IIRC the programmable kelleys come limited to 90% max power.
but they're current limiting, so the motor is limited to draw no more than what 180 Amps (can't recall the controller peak amperage you bought tbh)
And w/o load I doubt it draws more than maybe 30-50 Amps even if you haven't removed the rear wheel (which in fact is already "load")

think about it this way: if you can easily move the 5.x:1 ratio driven rear wheel with two fingers back and forth in rapid succession by touching nothing but the chain then it's no load..
else it is

BUT you should never run a PMDC w/o load at full speed,
it'll not like it, so an attached rear wheel is the minimum I'd consider safe to floor
Motenergy for example asks you to never run any of their brushed motors above 5k rpm.. ever

Anyways back to RPV..
You more often than not read KV ratings for BLDC motors (especially on RC stuff)
And the way THAT works is the exact opposite of what most think it is..
DRIVEN at a specific speed, it can generate a specific voltage
(say a 200kv motor needs 500 rpm to generate 2.5 Volts)
And that is in fact more or less a constant.
But it does not mean that if you apply 25Volts it'll automatically spin 2000 rpm
since the commutation of a BLDC is purely electronical,
the controller can limit the speed to whatever value he finds plausible, he just cannot exceed the 2k rpm limitation.
(in fact due to losses he might have troubles hitting 1900 rpm)

And a similar thing happens with mechanical commutation;
it takes a moment (some ΅s) for the magnetic field of a coil to collapse
when it's disengaged,
so the faster a motor spins, the bigger the residual magnetic field in the disengaged coil at the time it passes it's magnet increasing the attraction between the two,
and the bigger the attraction the more the motor gets slowed down.

So it's essentially self braking at it's max mechanically possible speed.

And the reason you should NOT go there is,
that magnetic friction can go nowhere and causes a ton of heat,
so a tiny bit of load to the rotor is in fact a good thing
Much better than cooking your magnets off, burning the insulation of the coil wires, or melting heat cracking the epoxy fixing it in place

'sid
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  #29  
Old 08-19-2019, 03:43 PM
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Wow, just wow!
...tons & tons of useful info

I read over your replies, several times
...really helps me to "put it into perspective" & understand all of this stuff better

I even go back & read old ones like http://www.diygokarts.com/vb/showthread.php?t=33805
…it helps to clarify some stuff that I didn't understand (too good)


1.) VPR is only useful (to us) as an "indicator"?
...of like, what RPM's, most 1,000W MY-1020 motors should produce when (X) voltage is applied

Manta (he he)...what can I say?
(so, that's why no one else lists an RPV value in their specs)...got cha

2.) It would be best to test & find the "favored direction of rotation" of a motor
...& to run it that way, for best performance (highest RPM's & efficiency)
...& to reduce the "extra" heat build up

3.) Yes, the 8,000W motor on my El Moto seems to be a "sibling" of the ME0709 (size & weight)
...but, the specs don't seem to match too well (if my Amp/Volt meter is anywhere near correct)

For example, Motenergy
http://motenergy.com/me0709.html

"The ME0709 is a Brush-type Permanent Magnet DC motor. Light weight, high efficiency design. Designed for 24-72 VDC battery operated equipment. Capable of 300 amps peak (1 minute) and 125 amps continuous. Totally open, fan cooled motor. Motor weight of 36 pounds."

...but, I've seen the Amp/Volt meter, on El Moto, read over 500A many times (just for a split second)
IIRC the highest was 563A

Maybe closer to the specs for a ME1003
http://motenergy.com/me1003.html

"This ME1003 is a Brush-Type, Permanent Magnet DC motor with very high efficiency. Capable of 11.5 KW continuous and 20 KW for 30 seconds (at 72 VDC). For voltages from 12 to 72 VDC input and 200 amps continuous (400 amps for 30 seconds ). Designed for battery operated equipment. Motor weight of 39 pounds."

It seems like the main difference is "if" the motor has single brushes (8)
...or double brushes (16)
(I have not looked inside of my motor to see which it is...yet)

* For the record, I am running a Kelly KDZ 72550 (up to 72V & 550A)
(it's the one that you recommended, after we did the Ohm tests on my motor, a few years back)
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  #30  
Old 08-19-2019, 08:24 PM
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yeah, I haven't re-read the old thread to check what controller it was ..
and I didn't remember all the specs we've discussed over there but since it didn't matter much
I was too lazy to check

Amp spikes can be anything really... and if you say they're more or less hiccups,
they don't tell anything about the motor (maybe about the condition of the brushes)
a sparking brush (you know that fancy ozone smell old motors tend to have..)
can cause such spikes

Then it could be due to a non smoothed amp meter.
Since an AmpMeter doesn't need a high refresh rate I was assuming the chinese
averaged over several dozen readings until they show a value (like 100 or more readings)
since it's cheap and reduces the chance of misreadings drastically,
but that might've been a flase assumption *shrugs*

There are plenty reasons for false readings actually
Above mentioned sparks, or simply a refresh rate matching rpm and commutator bar count
(thus it reads twice the power at certain times)
or say the voltage drops for some reason
like a battery hiccup or switched on consumer [brake lights]
and the ΅C wasn't updating the source voltage quick enough
it assumes a bigger voltage drop over the shunt (thus shows higher amps)

Or it's simply a math issue,
like a DAC inaccuracy (10bit dac can only read 1024 different voltage values and rolls over)
or a floating point issue (binaries cannot hold accurate decimals too well..)
many things can go wrong with digital measurements (especially on cheap meters)

That's the reason you can buy a multimeter for 10 bucks in a hardware store for hobbyists
and one for 700 or more for professionals that both do more or less the same thing
[same goes for digital calipers and so on and so forth]

hiccups in either directions ought to be ignored with meters in our price range let's say
And taking care of such misreadings is the reason professional meters are terribly expensive.

Try a constant load run ..
a long stretch uphill, max throttle for several seconds..
the number that shows up MOST is the one you care about

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  #31  
Old 09-20-2019, 07:08 AM
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I been doing some RPM tests on the 60V 2,000W brushless Boma motor that's powering the Atom kart.

Doin' separate tests for each of the low, medium & high speeds.

Each test is on a fully charged & rested overnight, battery pack.

The first low speed test showed an average highest RPM of 320
…& the highest that I saw was 348 RPM's.
(* these are axle RPM's)

Then, we do the math (the Atom kart has a 5.4:1 gear ratio)

So, it looks like low speed, on this 60V 2,000W set-up, seems to produce:

Avg. 320 x 5.4=1,728 RPM's
Max. 348 x 5.4=1,879 RPM's

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Old 09-20-2019, 05:01 PM
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yeah that's looking good.. well a ziptie would've helped, huh *giggle*

Anyways a solid 320 one and 340 the other way makes an average high of 330 for me.
(you did run up and down the same street twice, correct?
that was quite difficult to tell for sure with that viewing angle
but yeah I'd call that an 1780 rpm average
(unless someone would wanted to do a time rpm diagram and calcualte the seconds/half second baseline and std deviation of course )

Now the interesting bit..
the dash recording..
I still assume it's been the same road again being traveleld up and down..
so you can clearly tell it's indeed a slight incline (too lazy to calculate how big that'd be)
"up"hill W320 rpm ~980 Watts "down"hill 340 Wrpm ~ 700Watts on average and about two amps less drawn.

Smart limiting is a pain ain't it..
great for driving, but unfortunately when additional power can be used to accelerate
(1400++ watts at takeoff If I've seen that correctly 20+ amps) and the limiter only kicks in when you're already at speed ....

So what I think is happening (you'd need to check the programming) the controlelr limits to
about 15Amps as soon as motor rpm exceeds 1800 rpm (maybe 1750?)
and likely uses some exponential curve below..
Nevermind!

nice details to play around with!
motor sounds very happy even with the 'lowspeed' setting.
and it clearly shows how little power (less than a kW mostly)
can pack alot of fun

thanks for sharing.

'sid
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  #33  
Old 09-21-2019, 07:14 AM
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Quote:
Originally Posted by itsid View Post
yeah that's looking good.. well a ziptie would've helped, huh *giggle*

Anyways a solid 320 one and 340 the other way makes an average high of 330 for me.
(you did run up and down the same street twice, correct?
that was quite difficult to tell for sure with that viewing angle
but yeah I'd call that an 1780 rpm average
(unless someone would wanted to do a time rpm diagram and calcualte the seconds/half second baseline and std deviation of course )

Now the interesting bit..
the dash recording..
I still assume it's been the same road again being traveleld up and down..
so you can clearly tell it's indeed a slight incline (too lazy to calculate how big that'd be)
"up"hill W320 rpm ~980 Watts "down"hill 340 Wrpm ~ 700Watts on average and about two amps less drawn.

Smart limiting is a pain ain't it..
great for driving, but unfortunately when additional power can be used to accelerate
(1400++ watts at takeoff If I've seen that correctly 20+ amps) and the limiter only kicks in when you're already at speed ....

So what I think is happening (you'd need to check the programming) the controlelr limits to
about 15Amps as soon as motor rpm exceeds 1800 rpm (maybe 1750?)
and likely uses some exponential curve below..
Nevermind!

nice details to play around with!
motor sounds very happy even with the 'lowspeed' setting.
and it clearly shows how little power (less than a kW mostly)
can pack alot of fun

thanks for sharing.

'sid
Thanks,

Yup, same (2) block stretch, back & forth several times
…& correct, one direction goes slightly up hill

Boma 60V 2,000W low gear avg. RPM = 1,780

"Smart Limiting"?
…@ full speed/throttle, on the down hill section, I could feel the motor cut-out for a few seconds
(happened more than once)

Yup, lots of fun

Next up was the med gear RPM tests (even more fun)

The average highest RPM seemed to be ~600
…& the highest I saw was 639 RPM's

Avg. 600 x 5.4 = 3,240 RPM's
Max. 638 x 5.4 = 3,450 RPM's


* Love the explanation/information on the dash data
...more would be GREAT!

Here is the med gear test & dash data video

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Old 09-22-2019, 02:12 PM
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Default Boma 60V 2,000W High Gear RPM Test

High Gear RPM tests

I had to do these tests on another street, because it takes a lot longer stretch to reach top speed
(like 3 -4 blocks)

The average highest RPM reading, that I saw seemed to be ~800
…& the highest reading was 910 RPM's

* It's getting harder to get consistent data
...higher speeds/RPM's = it takes longer to get there & maintain consistently
…& there's lots more jostling around


Avg. 800 x 5.4 = 4,320 RPM's
Max. 910 x 5.4 = 4,914 RPM's

Average High RPM of 950 x 5.4 = 5,130 RPM's

Here is the video

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Old 09-22-2019, 02:35 PM
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You need a GoPro, Kevin...
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