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-   -   Digital RPM Meter (https://www.diygokarts.com/vb/showthread.php?t=41655)

Functional Artist 07-09-2019 09:20 AM

Digital RPM Meter
 
3 Attachment(s)
Over the winter I ordered a

Tachometer RPM Speed Meter 4 Digital Blue LED + Hall Proximity Switch Sensor (~$10.00)

https://www.ebay.com/itm/New-Tachome...orig_cvip=true

Specification:
Power requirement: DC 8-15V
Measure range:5-9999RPM
Clear zero:Automatic
Clear zero time:about 10s. the greater the RPM value,the longer the clear zero time
Refresh frequency: 0.2-0.5S(120-1200RPM);0.25-0.06S(2400-9999RPM)
Measure indication:RPM<5000,±2;RPM>5000,±3
Display:Blue 0.56" LED
Sign: Pusle signal,NPN 3 wires normally open
Response frequency:100HZ
Tachometer dimension:72x36x20mm,panel cutout Dimension:68x33mm
Hall proximity model:NJK-5002C
Sensor dimention: M12x10x37mm
Detection range: 1mm-10mm
Proximity output current: 200mA
Detected objects: Magnet
Sensor wiring:brown-Power+;blue-Power-;black-signal
Operating temperature: 0 to 50°C.

...to get some "real" data, on the "actual" RPM's, that some of these small electric motors, that we have been working with, are producing :thumbsup:

...unloaded & also loaded :cheers2:

mckutzy 07-09-2019 10:08 AM

This is cool... Ive been waiting for someone to do a writ up on this... I actually forgot about these.....
I was going to get one of these awhile ago... I was going to see if I can rig it to the blower housing to take reading off of the flywheel magnet..... but the HE sensor needs to read a certain magnetic polarity for use...

I found that itll work based on the measurements given.. in theory that is... but Im curious as to your input of these....

In the search on these devices... I found that people have used them for all sorts of rpm reading things, cause its really self sufficient; mount, apply magnet, maintain gap, apply power.....
A Cool one I saw, was for a drill press, just mounted to the quill and was able to get a really good reading...

---------- Post added at 09:08 AM ---------- Previous post was at 09:06 AM ----------

A secondary question to above......
With this device how much of a fuse value would you need to use? say in a stand alone or even automotive use?

Functional Artist 07-09-2019 10:55 AM

Quote:

Originally Posted by mckutzy (Post 528239)
This is cool... Ive been waiting for someone to do a writ up on this... I actually forgot about these.....
I was going to get one of these awhile ago... I was going to see if I can rig it to the blower housing to take reading off of the flywheel magnet..... but the HE sensor needs to read a certain magnetic polarity for use...

I found that itll work based on the measurements given.. in theory that is... but Im curious as to your input of these....

In the search on these devices... I found that people have used them for all sorts of rpm reading things, cause its really self sufficient; mount, apply magnet, maintain gap, apply power.....
A Cool one I saw, was for a drill press, just mounted to the quill and was able to get a really good reading...

---------- Post added at 09:08 AM ---------- Previous post was at 09:06 AM ----------

A secondary question to above......
With this device how much of a fuse value would you need to use? say in a stand alone or even automotive use?

Hey mckutzy

Looks like it
...but, I dunno, were gonna find out. :thumbsup:

As far using as a fuse,

According to the specs:
..."Power requirement: DC 8-15V
...& Proximity output current: 200mA"

Kinda small values
...& the diagram doesn't show a fuse
...so, I gonna skip it (for now) :2guns:

But, to answer your question, in an automotive situation it looks like 12VDC will power it fine
…& probably a 12V 1A - 3A automotive type fuse should be adequate protection :cheers2:

mckutzy 07-09-2019 12:56 PM

In this case what would be the proper power supply, wire gauge to use? 12ga?

itsid 07-09-2019 08:35 PM

the meter itself draws maybe 200mA (I'd say closer to 100 tbh)
the proximity sensor doesn't need 300mA at all
(maybe for 300kHz but that'd equate to 18 million rpms and I haven't seen anything that spinny yet ;))
It might still draw the full amps though (totally unneeded for the task at hand)
I use Honeywell 495As hall sensors and they can be powered by the chips output pin (20mA or less) and are still quite responsive .. at least good enough for something like such tach ;)
something with an internal comparator makes more sense for such task,
but I only have smd parts (salvaged off a bldc cd-rom motor)
5mA good for the 30k rpm the bldc is able to run at [model escapes me atm] ;)

Anywhoo, four seven segment led ~10mA per segment I guess..
makes 70mA per digit.. 280mA max..
usually they use pov so no more than three leds are on at once (30mA per digit... makes 120mA) especially since that saves a led driver chip and all leds can be powered of the microprocessor directly (which I guess can provide no more than 200mA in total)

Sooo at worst that thing draws 500mA;
I'd say the chip and stuff draws 15mA maybe 20.. the display should be good with less than 150mA and so it all comes down to the proximity sensor... if it actually draws 300mA or is cool with 50mA [as it should])

So in total I assume something like 250mA or less (depending on the number displayed)
So awg 20 should do really; 16 if you want to dial in on the safe side ;)

Fuse.. a 500mA quick should protect all internals but I doubt it'd be needed really.

'sid

mckutzy 07-09-2019 11:19 PM

Im really not that knowledgeable in the electronic field, I just know everything is needs to have certain things in a fashion or things burn up... But thanks for breaking it down....
I kinda understand...

This is cool... So even a/couple of 9v batteries could do the trick with out a fuse???

FA- what kinda things were you thinking about using this for???

Functional Artist 07-11-2019 11:16 AM

Quote:

Originally Posted by mckutzy (Post 528320)
Im really not that knowledgeable in the electronic field, I just know everything is needs to have certain things in a fashion or things burn up... But thanks for breaking it down....
I kinda understand...

This is cool... So even a/couple of 9v batteries could do the trick with out a fuse???

FA- what kinda things were you thinking about using this for???

Yup, that was a really good/in-depth analysis, Thanks Sid. :thumbsup:

I gonna set this (1) up as a mobile/hand held style meter
…& run it off of a (1) 9V battery :2guns:

Kinda like the hand held Amp/Volt meter I assembled during/for use with El Turbo
http://www.diygokarts.com/vb/showthread.php?t=36894
(the meter part starts @ post #51)

I mainly want to use it to get some RPM data on these MY1020 & ZY102 motors
...then, ??? :huh:

Functional Artist 07-11-2019 02:23 PM

9 Attachment(s)
Here is the meter (front & back) :thumbsup:

I did some measuring (it looks like ~2 3/4" x 1 3/16")
…& marking (used a pencil & a square)

* I'm using another piece of plastic from an old TV back
…& gonna use a small plastic box for the back cover :cheers2:

** I did all of the marking & cutting on the (smooth) back side
...so, if I messed up/slipped & scratched the surface it wouldn't be visible on the (textured) front side :cool:

*** I also put a scrap piece of cardboard on the work bench
...as to not scratch the front side, while I'm workin' on the back side :2guns:

Functional Artist 07-12-2019 06:18 AM

6 Attachment(s)
The back cover/box is ~2" x 3" x 2"
...so, the display, a 9V battery & an on/off switch should fit inside. :thumbsup:

Below are the diagrams I drew up

First, I just redrew the (factory) diagram (for quick reference)
...then, I drew a diagram including the battery (power supply) & the (on/off) switch :cheers2:

Notice, the wire colors are no where near consistent :ack2:
...Chinese ingenuity? :huh:

Positive (+) :
red (meter) to brown (sensor)

Negative (-):
black (meter) to blue (sensor)

Signal:
yellow (meter) to black (sensor)

* The switch that I'm using is "technically" a (3) way, on/off/of switch
...but, I'll only be using (2) poles (on & off) :cool:

** There wasn't room for the switch on the "face" & to still fit inside of the box
...so, I just installed it (inconspicuously) on the side

*** The display will fill, most of, the front of the box
…& the battery, switch & wiring/connections will reside in the back :2guns:

Functional Artist 07-12-2019 10:44 AM

6 Attachment(s)
Industrial Velcro secures the 9V battery in place :thumbsup:
...but, didn't get any pics :mad2:

Wiring
I wired the positive (+) battery lead (red wire) to (1) pole of the switch
…& then, connected another piece of (red) wire from the other pole to the red/brown wire-junction

The negative (-) battery lead connects straight to the black/blue wire -junction

The signal circuit wires (yellow/black) simply connect together :cheers2:

After shrink wrapping all of the connections I gently tucked the wires into the box
...& then, bolted the face plate to the box, with a couple of 3/16 Allen head bolts/lock nuts


Here is our hand held digital RPM meter :2guns:

* I mounted the box ~1/2" above the bottom of the face
...so, the meter will sit nicely & it will also hold the display so it's facing upward, just a bit :cool:

** Also left some extra plastic, above the display for maybe :idea2:
...a hole (to hang it on stuff)
...or a clip (to clip it on stuff)
...or ?? :huh:

Functional Artist 07-18-2019 10:35 PM

10 Attachment(s)
Picked up some more magnets :thumbsup:
...for testing different stuff (motors/karts)
...may have to "glue" 'em on

These magnets are a bit smaller
...but, should be strong enough to activate our sensor. :idea2:

* just noticed that the sensor has a small red light that's lit when the meter is turned on.

So, for a quick test (to see if this thing even works) I stuck the "stock" magnet to the rear "driven" sprocket on the El Mini (electric mini bike)
…& just held the sensor (by hand)

** The 10T "drive" sprocket on the motor is too small to attach a magnet to

So, we'll just take our readings off of the bigger 75T rear sprocket
...& then, do some math :cheers2:

Here is a quick video of this first (unloaded) test :2guns:

https://www.youtube.com/watch?v=1iEcG92Q-rg

Functional Artist 07-21-2019 08:11 PM

3 Attachment(s)
I came up with a quick, simple (maybe temporary, depending on how well it works) sensor mounting bracket
...just "zip tied" it to a small, plastic, squeeze clamp :thumbsup:

This way, I can simply "clamp it" on to a bar, somewhere close to the tire
…& it's easily adjustable :cheers2:

So, here is a video of my "loaded" RPM test :2guns:

https://www.youtube.com/watch?v=8OcsGzFQ7Pw

Functional Artist 08-01-2019 07:24 AM

1 Attachment(s)
Here are the RPM tests results for El Mini with the ZY-1020 (GD) 48V 1,000W motor & a 7.5:1 gear ratio :thumbsup:

Since were taking our readings from the rear sprocket, we will have to do some math
...& multiply the RPM reading by the gear ratio, to get the "actual" motor speed)

Unloaded Test
470 (on the meter) x 7.5 (gear ratio) = 3,525 RPM's


Then, if we divide the RPM reading, by the voltage were runnin' at
...we will get the RPM's per volt that this motor is producing
3,525/48V = 73.4 RPM's per volt

Loaded Test
430 x 7.5 = 3,225 RPM's
3,225/48V = 67.1 RPM's per volt

* The label on this ZY-1020 (GD) 48V 1,000W motor lists 2,800 RPM's
(most MY-1020 48V 1,000W brushed motors are rated @ 3,000 RPM's)

According to these tests, they seem to produce a bit more than that
...even under "load" :2guns:

itsid 08-01-2019 10:47 AM

you sure?

Since the usual 12V battery has a 13.5V output when fully loaded
we talk 54V fresh and 48V semi depleted..

that'd be 3133 rpm unloaded and 2866 rpm loaded [@48V]
So my guess is, you tested with fully charged batteries and w/o your voltmeter attached ;)

'sid

Functional Artist 08-02-2019 05:40 AM

Quote:

Originally Posted by itsid (Post 529879)
you sure?

Since the usual 12V battery has a 13.5V output when fully loaded
we talk 54V fresh and 48V semi depleted..

that'd be 3133 rpm unloaded and 2866 rpm loaded [@48V]
So my guess is, you tested with fully charged batteries and w/o your voltmeter attached ;)

'sid

I just posted what the tests seemed to show :huh:

I recorded these tests (did ya watch the videos?)

I did the unloaded test twice & got same results
...the loaded test was a several block ride
(it looked like 430 on the meter, several times)


Yes, these are brand new, fully charged batteries 12V 12AH batteries

No, I did not have any other meters attached


What factors did you use to get "3133 rpm unloaded and 2866 rpm loaded [@48V]"?

itsid 08-02-2019 06:49 AM

Quote:

Originally Posted by Functional Artist (Post 529928)
Yes, these are brand new, fully charged batteries 12V 12AH batteries

No, I did not have any other meters attached


What factors did you use to get "3133 rpm unloaded and 2866 rpm loaded [@48V]"?

simple.. assuming 54V (13.5V per battery)
dividing your results by 54 (rpm/volt to be 65.278 unloaded and 59.72 loaded)
then multiplying by 48 again to get the rated value

That's why I was asking about the voltmeter..
since again a fully charged 12V battery does NOT have 12V it's 13.5V or thereabouts.

'sid

vybrano 08-04-2019 07:24 AM

How did you attached magnet? Is it possible to measure speed with it? (I mean display actual speed, not calculate it out of RPM or something)

itsid 08-04-2019 07:50 AM

sure you can measure speed with it..
"actual speed " is a relative term tbh..
but if you know the effective circumference of the wheel* you can calculate it with the
measured wheel rpm.

and no, that is the ONLY way to measure road speed.. wheel rpm times circumference;
unless you want to use a GPS speed (which is less accurate most of the time)

attaching... superglue works well but IDK what Kevin did to attach it permanently.
(or if at all)

'sid

* effective circumference is calculated by the height of the wheel under load (center axle to road with you in/on the vehicle) and Pi, it's NOT the nominal nor measured circumference at rest!
ideally, you hop on/in and use some chalk marker across the tread, then roll (legs up) and measure the markings on the garage floor ;)

Functional Artist 08-13-2019 06:47 AM

1 Attachment(s)
Quote:

Originally Posted by itsid (Post 529930)
simple.. assuming 54V (13.5V per battery)
dividing your results by 54 (rpm/volt to be 65.278 unloaded and 59.72 loaded)
then multiplying by 48 again to get the rated value

That's why I was asking about the voltmeter..
since again a fully charged 12V battery does NOT have 12V it's 13.5V or thereabouts.

'sid

Those are some very good points, glad your around :thumbsup:
...so, I checked for ya, the battery pack on El Mini sits @ ~53.4V fully charged. :cheers2:

New questions::idea2:
For calculating purposes is it "standard practice"
...to use 53.4V? (3,525/53.4=66.01 VPR) (volts per revolution)
...round it off to 53V? (3,525/53=66.5 VPR)
...or to also factor in the voltage drop (~1V while running) & use 52V? (3,525/52=67.7 VPR)

itsid 08-13-2019 09:07 AM

I think that depnends on how low your standard is ;)

standard practice for an industry conform check that require battery operation
is to add a voltmeter to the system and log the volts under load at speed (ideally as precise as possible)
some companies work with just two decimals of precision, some with three or more
(using strictly calibrated meters with known drop).

So don't worry about it too much,
with your tools you cannot achieve a perfect result anyways
and the result you get is certainly good enough for what we do around here
since none of that is "solid truth" anyways ;)
as long as we don't know the load specification for testing you cannot emulate that
and your load might be off by whatever unknown value.
(say a 2% error in the tach and a 1.3% error in the voltmeter)

even an ever so miniscule road inclination throws your values one way or another
so the only thing that'd make it a good result would be an average over a few runs on a dyno;
or precisely several different dynos to compensate their "errors"
that'd be an insane amount of effort for a home gamer.

So what you'd need is an average over several runs:
take a patch of road and do ten runs a day over ten days..
going up and down that same patch of road back and forth like a madman.
and keeping constant track of voltage and rpm (over the entire run)
but logging would be a pain, right..
(you can build such logger for a few dollars[<10 I'd say] if you want to I'll explain that later)
And then average out the results to get a really superb estimation
that should be within 1-2% of the proper lab-result.

'sid

Functional Artist 08-14-2019 10:27 AM

Thanks, many more good points :thumbsup:

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 :cheers2:

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. :2guns:

itsid 08-14-2019 05:42 PM

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.

'sid

Functional Artist 08-14-2019 11:28 PM

2 Attachment(s)
Kool! :cheers2:

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

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? :idea2:

Here is a video of the tests :2guns:

https://www.youtube.com/watch?v=dfp8OjmV67k

itsid 08-15-2019 05:17 AM

Quote:

Originally Posted by Functional Artist (Post 530778)
…& got some interesting results :huh:

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? :idea2:

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

Functional Artist 08-15-2019 06:38 AM

Quote:

Originally Posted by itsid (Post 530789)
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 :cheers2:

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 :huh:

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? :ack2:

:idea2: 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 :smiley_omg:

itsid 08-15-2019 12:03 PM

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

Functional Artist 08-15-2019 03:10 PM

Quote:

Originally Posted by itsid (Post 530813)
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 :thumbsup:

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

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 :cheers2:

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

https://www.youtube.com/watch?v=O4mGLNnLrUs

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?

itsid 08-15-2019 08:16 PM

2 Attachment(s)
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
Attachment 110910
and COUNTER CLOCKWISE
Attachment 110911
diagrams :D
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 :D

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 :D
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 :D

'sid

Functional Artist 08-19-2019 03:43 PM

Wow, just wow! :smiley_omg:
...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 :cheers2:

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) :huh:


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 :cheers2:

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) :2guns:

itsid 08-19-2019 08:24 PM

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 :D

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 :D
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 ;)

'sid

Functional Artist 09-20-2019 07:08 AM

1 Attachment(s)
I been doing some RPM tests on the 60V 2,000W brushless Boma motor that's powering the Atom kart. :thumbsup:

Doin' separate tests for each of the low, medium & high speeds. :cheers2:

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) :2guns:

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

https://www.youtube.com/watch?v=ey2d9fC7R2o

itsid 09-20-2019 05:01 PM

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! :thumbsup:

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 :D

thanks for sharing.

'sid

Functional Artist 09-21-2019 07:14 AM

Quote:

Originally Posted by itsid (Post 533249)
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! :thumbsup:

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 :D

thanks for sharing.

'sid

Thanks,

Yup, same (2) block stretch, back & forth several times :thumbsup:
…& correct, one direction goes slightly up hill :cheers2:

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 :2guns:

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 :cool:

https://www.youtube.com/watch?v=RR3Ec6-o4nk

Functional Artist 09-22-2019 02:12 PM

Boma 60V 2,000W High Gear RPM Test
 
High Gear RPM tests :wai:

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

The average highest RPM reading, that I saw seemed to be ~800
…& the highest reading was 910 RPM's :2guns:

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


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 :cheers2:

https://www.youtube.com/watch?v=7TLbVOJEa8c

JTSpeedDemon 09-22-2019 02:35 PM

You need a GoPro, Kevin...


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