Anybody here know BLDC motors well?

Guest
I want to use a hobby BLDC motor to power a compact high speed
spindle to be used for engraving and the like. Mainly because they are
so compact for the power and speed. I cannot find, for a price I can
justify, a 24,000 to 40,000 RPM spindle that will fit in the space I
want to put it.
Looking at some hobby BLDC motors and then buying some to
experiment with leads me to think that one of these motors may work.
I have looked online for answers about these motors and maybe I'm
just dense (good possibility) but I haven't been able to find exact
answers. Maybe someone here can help.
Motors are rated RPM/volt. This means maximum RPM per volt of
course. If the motor is supplied with a higher voltage from a supply
that limits the current to stay below the specs of the motor will
higher RPM be possible?
The ESCs (Electronic Speed Controller) are voltage and current
rated. Could the output an ESC rated for a lower voltage and current
be used to drive control power transistors in order to get around the
lower voltage and/or current rating if a sensored motor is being used?
I don't need to use a hobby ESC but they are plentiful and cheap.
And all assembled. Which is most important. But I would be fine using
some other BLDC motor driver in order to get the desired RPM that I
want.
I can do all the precision machining necessary to make the spindle
that will hold the carbide cutting tools and to interface the motor
with the spindle. I do not yet know enough about balancing in order to
dynamically balance a motor which causes too much vibration from an
out of balance condition but I think I can learn enough to do it. I am
good with mechanical systems and have a pretty good intuitive feel for
them. It's the electronics I'm not so good at.
Thanks,
Eric
 
If you (spendy) source a servo-rated BLDC motor, it will tolerate all sorts of abuse, and may be loaded to a dead-stop without damage. And, if you are going to be doing this - purchase the correct speed control rated for the full shorted load of the motor. As there are no brushes, that is not the same as a short-circuit as it would be in a brush-type DC motor.

Peter Wieck
Melrose Park, PA
 
I have played around with these motors making drones from scratch. You can't just buy a motor and ESC connect them together and have it run. The input to the ECS is a pulse that varies in width for the desired speed of the motor. the direction of spin is controlled by how the 3 wires to the motor are connected (reverse any 2 and the motor spins in the opposite diredtion).. I have run these motors without the cpu controller that makes a drone fly but you need 2 things. A wireless control transmitter that usually has joy sticks to control the speed and direction of the drone (Usually $50 on up). A receiver that can be directly connected to the input side of the ESC to supply the appropriate pulse to the ESC (about $15). The ESC supplies the 5v back to the receiver so no extra power supply is needed other that the high current one used to power the ESC itself.

There are probably controllers that can be used with these BL motors directly but I have not researched these. Since the price of a wireless controller/receiver pair is so low I doubt that a dedicated controller would be worth the cost. If you were an electronics hobbyist you could build a controller that would supply the correct pulse to the ESC.

Hope this helps.

....bob
 
One more thing - an unbalanced motor spinning at 24,000 + rpm will destroy itself in short order. I suspect that the motor itself will be the least of your worries.

At the same time, is this engraving device for a pantograph, or similar, such that an off-the-shelf engraver would not be suitable? There are some pretty good ones out there.

https://www.gesswein.com/p-2557-foredom-power-graver.aspx?gclid=CjwKCAjw8r_XBRBkEiwAjWGLlESlB2zvwLG2Covx4zMNmIheomOHFURpCrIzKeQWP7pGlPkjFtI3GxoCs5QQAvD_BwE

That for the price will probably be competitive with your home-brew at the end of the process.

Peter Wieck
Melrose Park, PA
 
On Mon, 7 May 2018 06:29:53 -0700 (PDT), bobrweber@gmail.com wrote:

There are probably controllers that can be used with these BL
motors directly but I have not researched these.
Click to expand...

Ebay shows 700 listings for such controllers:
<https://www.ebay.com/sch/i.html?_nkw=brushless+motor+speed+controller>
Most are for eBike and electric scooter speed controls but the smaller
boards might be usable.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
On Mon, 7 May 2018 06:51:25 -0700 (PDT), "pfjw@aol.com"
<peterwieck33@gmail.com> wrote:

One more thing - an unbalanced motor spinning at 24,000 + rpm will destroy itself in short order. I suspect that the motor itself will be the least of your worries.

At the same time, is this engraving device for a pantograph, or similar, such that an off-the-shelf engraver would not be suitable? There are some pretty good ones out there.

https://www.gesswein.com/p-2557-foredom-power-graver.aspx?gclid=CjwKCAjw8r_XBRBkEiwAjWGLlESlB2zvwLG2Covx4zMNmIheomOHFURpCrIzKeQWP7pGlPkjFtI3GxoCs5QQAvD_BwE

That for the price will probably be competitive with your home-brew at the end of the process.

Peter Wieck
Melrose Park, PA
Click to expand...
This engraving spindle is for use in a CNC mill. Ideally it will
sit in the tool carousel along with the other 20 tools and be
connected to power and cooling automatically. But I will probably need
to manually plug in power and cooling connectors.
I use different rotary tools for engraving and micromilling. The
smallest engraving tools I use are .015" diameter at the tip. The
smallest milling cutters I use are similar in size. The graver you
linked to is a hammer type and is not the type of engraving I do.
There are several ways to engrave and what my customers want requires
rotary tools. I am really just doing shallow machining when I engrave,
not any kind of artistic stuff. Letters, lines, numbers, that kind of
thing.
The top spindle speed of my main spindle is only 7,500 RPM. I do
have a sub spindle that spins at 24,000 RPM but it is too big to fit
in a CAT 40 tool and so is instead mounted in a clamp which in turn
clamps around the main spindle housing. A kluge.
I have some hobby BLDC motors but the ones with enough power for
high feed rate cutting max out at 24,000 RPM and I really want 40,000
RPM. I have experimented with the motors spinning a tool at 24,000 RPM
and surprisingly the things were pretty well balanced. But as I said
they can't be fed along very fast.
Eric
 
That makes a lot more sense in terms of your request.

https://www.maxonmotorusa.com/maxon/view/content/ec-motors


Gets you up to 120,000 rpm. I expect that they will be pretty well balanced as well.

Peter Wieck
Melrose Park, PA
 
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