[chbot] Stepper Motor Checking
Simon Knopp
shrunken.apple.head at gmail.com
Thu Jul 7 04:53:29 BST 2011
I wasn't trying to be academic or argue over
ounces/feet/pounds/inches/newtons/metres. Sorry if it came across that way.
I just thought that as a group of roboticists we should be clear on
something as fundamental as torque. I figured this list is about helping
each other out, so I was trying to be helpful by correcting an error.
Good work finding the article, it looks like a useful technique.
Simon.
On Thu, Jul 7, 2011 at 3:12 PM, Mark Beckett <m.beckett at amuri.net> wrote:
> Simon
> If the authors terms spelling or otherwise offends or confuses you, then
> simply move on.
>
> If you are so keen on Foot pounds of torque then divide by 192.
> The actual method of checking is correct, which is what the article was
> about.
>
> The reason I presented it to the group, was it was a relatively easy
> means to check an otherwise unknown stepper motor.
>
> /While the academic amongst the group argue over the correctness of the
> written theory, the more practical will have done any checks and moved on./
>
> Mark
>
>
> On 7/07/11 14:26, Simon Knopp wrote:
> > Your quoted excerpt makes my point: torque is measured in *ounce
> > inches*, not ounces per inch. Torque = force x distance, not force /
> > distance.
> >
> > Ounce(force) per inch would be a valid unit for stiffness, not for
> > torque.
> >
> > Simon.
> >
> >
> > On Thu, Jul 7, 2011 at 2:12 PM, Simon Chester <simonches at gmail.com
> > <mailto:simonches at gmail.com>> wrote:
> >
> > It's not incorrect: http://en.wikipedia.org/wiki/Torque#Units
> >
> > In British unit, "pound-force-feet" (lbf x ft),
> > "foot-pounds-force", "inch-pounds-force", "ounce-force-inches"
> > (oz x in) are used, and other non-SI units of torque includes
> > "metre-kilograms-force". For all these units, the word "force"
> > is often left out, for example abbreviating "pound-force-foot"
> > to simply "pound-foot" (in this case, it would be implicit
> > that the "pound" is pound-force and not pound-mass).
> >
> >
> > On Thu, Jul 7, 2011 at 12:07 PM, Simon Knopp
> > <shrunken.apple.head at gmail.com
> > <mailto:shrunken.apple.head at gmail.com>> wrote:
> >
> > I stopped reading the first link when I saw "...torque is
> > usually measured in ounces per inch". A whole page about
> > measuring torque prefaced by an incorrect definition. Oops.
> >
> > Simon.
> >
> >
> >
> > On Thu, Jul 7, 2011 at 11:43 AM, Mark Beckett
> > <m.beckett at amuri.net <mailto:m.beckett at amuri.net>> wrote:
> >
> > Since there is a dgree of interest around steppers
> > I found this while searching for something else.
> >
> > http://www.romanblack.com/stepper.htm
> >
> > I'm sure the members could improve on the glue it down
> > approach.
> > Also he is measuring the hold torque, which will be
> > different to the
> > rotating torque.
> >
> >
> > For Robin
> > He has a very interesting section on one wire
> > http://www.romanblack.com/blacknet/blacknet.htm
> >
> > For those folowing the CNC he has this
> > http://www.romanblack.com/cnc_good.htm
> >
> > Mark
> >
> >
> > On 4/07/11 16:43, HARTLEY, ROBIN (ROBIN) wrote:
> > > Hi,
> > > I've looked at the trim routers and initially
> > disregarded them as they are 1/4 chuck, rather than 1/8,
> > and a lot heavier than a dermal.
> > >
> > > After destroying 2 home made spindles, 1 after 10 hours
> > work cutting ali which I think was an air flow issue& the
> > next after 20 minutes because it was a cheap armature, I
> > may well look at the trim routers again.
> > >
> > > The extra weight puts higher demands on the Z axis,
> > which in my case is where I found out all about some
> > uni-polar steppers not liking bi-polar drive with PWM.
> > >
> > > Due to my design I'm a bit limited on space& I got
> > another stepper but it has the same problem.
> > >
> > > There was a comment in this thread about speed control,
> > here's my experience.
> > > Most of these home made machines are routers rather than
> > mills& so cut with a very fine feed so you only need
> > enough speed rather than managing a speed feed
> > relationship of a mill where it produces chips.
> > >
> > > My approach is to do a test piece run and adjust the
> > depth of cut to keep chatter under control, almost
> > impossible with a plastic cased dermal.
> > > I then ramp the speed up until I here the spindle start
> > to load significantly, I can hear the speed drop, then set
> > my G code to run up to about 50% of that feed rate.
> > >
> > >
> > > With a home made spindle, which is basically a cheap
> > dermal knock off removed from it's case and ali blocks
> > for bearing mounts, I can cut 2mm deep at about
> > 150mm/minute feed.
> > >
> > > The secret to cutting ali is to keep it flooded with
> > coolant. In my case I use lots of CRC. I basically stand
> > there with a spray can& keep the grove full of CRC.
> > >
> > >
> > > For any one building a machine alignment of the feed
> > screws is the biggest issue. What worked for me is to
> > mount a bearing on the lead screw on the opposite end from
> > the motor& clamp the lead screw against for/aft movement
> > and at the motor end I use a piece of rubber fuel line as
> > a coupler. The modern reinforced fuel injection line has a
> > lot of reinforcing that prevents twist.
> > > For lead screws I use 8mm threaded rod, 1.25mm per
> > turn,& for the nuts I use a piece of plastic chopping board.
> > >
> > >
> > >
> > >
> > >
> > >
> > > Regards,
> > > Robin
> > >
> > >
> > >
> > >
> > >
> > >
> > > -----Original Message-----
> > > From: chchrobotics-bounces at lists.linuxnut.co.nz
> > <mailto:chchrobotics-bounces at lists.linuxnut.co.nz>
> > [mailto:chchrobotics-bounces at lists.linuxnut.co.nz
> > <mailto:chchrobotics-bounces at lists.linuxnut.co.nz>] On
> > Behalf Of Chris Hellyar
> > > Sent: Saturday, 2 July 2011 11:03 a.m.
> > > To: Christchurch Robotics
> > > Subject: Re: [chbot] building CNC router - was Free
> > stepper motors
> > >
> > > 'Urro...
> > >
> > > Given a dremel new is $120-150 ish...
> > >
> > > Trim routers like these:
> > >
> > >
> >
> http://www.powertoolshop.co.nz/product_info.php/cPath/20_96/products_id/20
> > >
> > > For $119 with a full alloy body are a better bet.
> > >
> > > As I see it, it's cylindrical so it's easier to mount,
> > no speed control
> > > inbuilt so you can use a closed loop speed control on it
> > for better
> > > cutting in soft stuff. It'll also have higher rotor
> > inertia and a
> > > better quality chuck.
> > >
> > > There are a few on the market. When I last looked there
> > were a few
> > > options on the shelf at Bunnings/Mitre10 that looked good.
> > >
> > > I was specifically thinking dremel replacements for
> > wood/plastic/alloy
> > > cutting. If you're looking for dedicated spindle ebay
> > is probably your
> > > friend..
> > >
> > > And, having said all that, my next project is going to
> > be swinging a
> > > water cooled VFD spindle. I am sooooo over the noise of
> > brushed routers!!!
> > >
> > > Cheers, Me.
> > >
> > > On 02/07/11 10:17, Volker Kuhlmann wrote:
> > >> On Sat 02 Jul 2011 02:06:20 NZST +1200, Chris Hellyar
> > wrote:
> > >>
> > >>> There are some very reasonably priced options rather
> > than sticking with
> > >>> a dremel.
> > >> Can you elaborate?
> > >> And are these options for a dremel replacement or a CNC
> > spindle?
> > >>
> > >> Thanks,
> > >>
> > >> Volker
> > >>
> > >
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