On Thu, 23 Jun 2011 14:27:29 -0700 (PDT), wrote:

On Jun 23, 3:07*pm, wrote:
On Thu, 23 Jun 2011 13:42:27 -0700, Tim Wescott
wrote:





On 06/23/2011 10:10 AM, Robert Roland wrote:
On Thu, 23 Jun 2011 16:18:39 +0000 (UTC), wrote:

I've been interested in small brushless motors for some time and it
seems like the ones made for RC use are plentiful and cheap. Bujt I'm
having a hard time getting my questions answered about these things.
My uses will not be in some type of RC toy, but "toys" that I want to
make for myself. I know I will need to get an ESC to drive the motor.
But what kind of signal does the ESC need? The same type of signal
that RC servos use?

A plain, normal ESC will use the same signal a servo uses. It connects
to the receiver just like a servo. There are also special ESCs that
are controlled by SPI or similar. These are used where very quick
response times are needed.

Do I need to get a programming card for the ESC?

It depends. Some higher-end ESCs allow you to tune their parameters,
but they come preconfigured to working defaults, so will work fine in
most applications. Some ESCs are programmed using the throttle stick
in connection with beeps emitted through the motor, some need a
programming card, while others are connected to a PC. Some controllers
cannot be reconfigured at all.

And how is the rpm/volt detrermined?

It is determined by a number of factors, such as magnet strength,
number of windings, number of poles, physical size, and more.

I'm thinking that I should get a
kit motor to learn about them but I also want to get some regular
motors to compare.

I've never built my own motor, so I can't help you there.

It looks like Hobby King might be the best place to
buy the motors from but I don't know.

I have not (yet) dealt with them, but I have heard from numerous happy
customers, so they seem to be a decent outfit.

That's pretty much what I would say. *The only exception is that the
stuff Hobby King sells can have quality problems, both the kind that
causes infant mortality, and issues with long-term reliability and
robustness. *If you really want it to last, particularly if you're
stressing the bearings in any way, Hobby King's products may not be the
best.

AXI, eFlight, Scorpion, Castle Creations, and Plettenberg are all better
(1st tier, or almost so) motor brands that I know. *But they're more
spendy -- use the Hobby King stuff to get your feet wet, then go from there.

Thanks Rob, Winston, Cy and Tim,
I knew there would be someone here who would be familiar with these
things. I have two projects in mind. The first is a gyroscopic
stabiliser for a digital camera. I built a prototype with brass
flywheels and pager motors. It worked OK but the life of the pager
motors is low. And they were a little noisy. So I'm thinking that
maybe one of these new fangled three phase brushless motors used with
good bearings might work. I seem to remember downloading a circuit
built around a 555 timer that puts out the pulses used by servos. So
with a cheap ESC, LiPo battery, and brushless motor I might be able to
make a lightweight gyro stabiliser. The other project that I've been
working on is a spinning wheel with a brake on it. The idea is that
when the brake is slowly released the wheel will start to spin, with
less braking leading to faster spinning. So I need a motor that can
remain stalled without overheating. With a stalled brushed motor the
energy delivered is not shared equally by all the windings and so
maybe it will overheat. I don't know if the three phase brushless
motor drives keep energising windings in sequence when the motor is
stalled. This something I want to find out.
Eric- Hide quoted text -

- Show quoted text -

How are you dynamically balancing your rotors? Have been looking for
a small dynamic balancer that could be built by an individual without
bankruptcy staring me in the face. Would be of interest for doing a
bunch of projects involving high-speed revolving parts. Think model
turbojets...

As far as stalled rotors, a friction clutch is the usual solution,
motor doesn't see a real current spike that way. Just have to replace
the clutch if you wear it out from stalling too frequently.

Stan
Greetings Stan,
I'm trying to avoid slip ctutches. For a couple reasons. First, they
wear out, and second they tend to have higher breakaway friction than
running friction. I can buy special clutches that do not exhibit this
stick/slip problem but they are expensive. If anything the breakaway
friction should be lower than running friction. I'm hoping that I can
run a motor at a much lower current than it is rated for and so can
keep it stalled indefinitely. I didn't balance my rotors for the gyro.
They were machined carefully and all at once except for a facing cut
after being parted off. The parallelism was better than .0001" and
concentricity was basically perfect because all diameters were
machined at the same time.
Cheers,
Eric