BLDC motor speed notation?

[throbscottle]

Been looking for a cheap bldc motor on eBay, the more interesting ones have the rpm written as KV, eg 1000KV. I'm guessing it's not a Chinglish error, so any explanation?

Here's an example: **broken link removed**

 

[Les Jones]

I think it means that they rotate at 1000 RPM per volt applied. I do not know weather this the voltage applied to the controller or the peak output voltage per phase from the controller.

Les.

 

[MaxHeadRoom78]

The type of control on this motor is PWM and the motor is termed an Outrunner, i.e. the inner stator is stationary and the outer revolves.
Max.

 

[throbscottle]

Hmm, Ok that's interesting. I want speed more than torque, so I don't want one of those then. I was thinking of taking a motor from an old hard drive but it looks as though there may be too many problems associated with that idea. It's for a spindle motor for a tunsten carbide pcb drill. Has to have a 1/8" shaft. Any suggestions?

 

[Les Jones]

If the 10000 RPM that the motor you linked to is not fast enough I found one on ebay rated at 4800KV That would be 48000 RPM (At 10 volts)

Les.

 

[throbscottle]

I just saw "outrunner", looked it up and thought the eBay listing must be exaggerating the rpm's. I read somewhere on a similar kind of project that these drills need to run at least 10,000 rpm, though I've been using them at around 4000 rpm with no problem (the particular project I was looking at used an air motor - very impressive!). I worry that if it runs /too/ fast the crappy chuck I've got will vibrate too much due to it's grub-screw mounting.

So, the K doesn't mean thousand in this case, then.

 

[shortbus=]

Les was partly correct in post #2. It's a feedback voltage number from the motor to the ESC(motor controller). A motor listed 1KV means that the motor gives a signal of 1V for every 1000(K) RPM. This tells the controller how much duty cycle to set in the PWM of the output to the motor. The 1KV is a pretty much standard for a brushless motor, though some motors do differ. It comes from the back EMF of the motor windings. A link to explain more - https://www.rcgroups.com/forums/showthread.php?t=588177

If your using standard PCB drills with a 1/8 inch shank, your probably better off using a collet adapter. Will not run out as much as a drill chuck and be in balance more than a chuck. A link to the first one I found - https://www.banggood.com/0_5-3mm-Sm...let-Micro-Twist-Drill-Chuck-Set-p-952211.html

 

[Les Jones]

Hi shortbus=,
Thanks for explaining the correct meaning of the KV term. When I first saw these motors I took the K to be 1000. So I interpreted 1000KV as 1000000 RPM per volt which I decided it could not be. It is also strange that so many adverts for model servos quote the torque in KG when KG is not a unit of torque. I think thy normally mean KG cm.

Les.

 

[Tony Stewart]

k RPM per Volt is limited by rated voltage and is always rated with no load.

Together with the motor power rating and load power profile, you must determine if they are suitably matched at max speed or max acceleration depending on your requirements.

 

[throbscottle]

By crappy chuck I actually meant the versions of a collet chuck commonly available a year or 2 back that are 2 part assemblies - the jaws are part of the spindle attachment. Looks like things have improved a lot since then - when I wanted a chuck to fit 1/8" shanks I could only find one to also fit a 1/8" motor spindle, and standard DC motors with that size spindle are too slow!
So I need a smaller motor than the RC model ones, and not restricted to the 1/8" spindle any more, which is nice. It looks like the majority of bldc motors do what I need anyway.

 

[camerart]

Hmm, Ok that's interesting. I want speed more than torque, so I don't want one of those then. I was thinking of taking a motor from an old hard drive but it looks as though there may be too many problems associated with that idea. It's for a spindle motor for a tunsten carbide pcb drill. Has to have a 1/8" shaft. Any suggestions?

Hi T,

If you're still considering using a hard drive motor, they will work with the Brushless motor ESCs.

Camerart.

 

[throbscottle]

Nice to know, if the drive's own controller won't do it. Thanks

 

[gophert]

Nice to know, if the drive's own controller won't do it. Thanks

WC drill bits work just fine in any old drill press. Just take your time feeding the bit (which means about as fast as you want to). The 10k to 30k speeds are for when they are connected to high speed robotic drill heads that make 100s of holes per minute.

 

[throbscottle]

Oh I see! I did end up putting a standard motor with a bigger spindle on my old pcb drill and using them on it, worked ok. I just have that need for speeeeed now though...
Plus, I really do want to build a better drill

 

[gophert]

Oh I see! I did end up putting a standard motor with a bigger spindle on my old pcb drill and using them on it, worked ok. I just have that need for speeeeed now though...
Plus, I really do want to build a better drill

If your plunge speed is not matched with your RPM, you end up melting the plastic instead of cutting it. Look for chips and turnings. This is better than goo. Also, if the holes on the back side or the top side of your board looks like volcanoes instead of perfectly flat around the hole, you are melting the plastic around the hole instead of cutting.

 

[shortbus=]

WC drill bits

Hey Gopher, learned something today In using 'carbide' tools for ~50 years, never knew they could also be called by another name. I'm assuming the WC is short for Wolfram Carbide?

 

[throbscottle]

And there was me thinking it was a typo...

 

[gophert]

Hey Gopher, learned something today In using 'carbide' tools for ~50 years, never knew they could also be called by another name. I'm assuming the WC is short for Wolfram Carbide?

The tool users rarely use this notation. The metallurgist/material scientists use it at the carbide producers because there are so many material sold into many markets. Companies like Kennametal make tungsten carbide (WC), titanium carbide (TiC) and silicon carbide (SiC) and several others but these are the most common carbides - I've worked with so many industries over the years, some of that experience just spills out and I end up confusing people. Nice pickup on the WC!

 

[shortbus=]

I knew the wolfram = tungsten from back in my high school days. My school had something called T and I, trade and industry classes. Four periods a day for Jr and Sr years to learn a trade, machinist(what I took), drafting, carpentry, automotive mechanics, or commercial printing. Each class could have a "club" with jackets and a name. My class chose the name "wolframs".

 

[gophert]

I knew the wolfram = tungsten from back in my high school days. My school had something called T and I, trade and industry classes. Four periods a day for Jr and Sr years to learn a trade, machinist(what I took), drafting, carpentry, automotive mechanics, or commercial printing. Each class could have a "club" with jackets and a name. My class chose the name "wolframs".

You old-school guys are great. The Germans still call it Wolfram.

My neighbor was a metallurgist and he was trying to alloy niobium with light metals to improve toughness. He was from Austria and insisted on calling Niobium (Nb), Columbium (formerly Cb). He said, "I am an American now. Americans discovered Columbium and named it 'columbium'. I will not start calling it Niobium just because a bunch of chemists and engineers in Europe decided it will be called Niobium." That guy was still consulting for a materials company in his mid-80s.