I have been asked by a co-worker if this would be difficult to build.
What we are looking to do is make a d.c. motor test machine. It needs to
do just a few things.
1. Test the rpm. No less than 10,500 RPM
2. Test the Amperes being drawn at that speed No More than 6.2 Amps.
3. Torque it can handle.
4. Horse Power of motor. no more than 1/8 H.P.
That's really about it.
As far as RPM goes I thought about using a small magnet and a hall
sensor. Let it sample for say 5 sec. the calculate it out. As for the
amps. A simple amp meter would work. Is there a way to read the amps and
then print it out or display a report ?
Measure Torque ??
H.P. can be done with the amount of watts that it draws. 1H.P. = 745
watts (I think)
Any suggestions on which pic to use? Or anything else I might need to
look at?
Please remember I'm just a hobbyist. Have only made a few simple things.
But I would like to figure something out. If noting more than just to
have a challenging project.
> 1. Test the rpm. No less than 10,500 RPM
> 2. Test the Amperes being drawn at that speed No More than 6.2 Amps.
> 3. Torque it can handle.
> 4. Horse Power of motor. no more than 1/8 H.P.
This is more fun than it looks, but it's doable.
What's the reason for doing the testing though? Production line, acceptance
of product, hobby, or something else?
RPM can be a hall device, or (easier to balance) just white and black tape
on the shaft. You have a counter on the pic, so you can count turns for a
while, then decide what to do with the result
Couple your motor to a DC generator (another motor) and measure output power
into a given load. Since the generator is a constant, the variable is the
motor under test.
Current can be done with a shunt or hall effect sensor (6A = 6 Gauss)
Torque is a fun measurement, I'm not sure that you can really do that one
easily. You need something like a prony brake. (it's torque at some
particular speed you want, right? Locked rotor torque is
position-dependent, and much easier to measure.
Horsepower in which terms, input or output? I'd want power out versus power
in.
rpm - how about an optical detector - dependent on your shaft arrangement
you may be able to look at a keyway or flat etc. - Anyway a disk would be
easier to balance at 10,500rpm than a magnet.
current - simple voltage drop across a known resistor.
torque
Is this at stall or as it varies with speed? Either way you'll need some
sort of brake and a force "measurer" such as a strain gauge etc. This side
of things could get as complex as you want - or as simple as a spring
balance, a hinge and a G-clamp.
For a PIC implementation a strain gauge feeding a A-D input & coupled with
the rpm measurement and some sort of friction brake should allow you to
produce "automatic" figure of torque, speed & current and send them to a PC
via the serial port. This could then produce any curves or provide database
storage as required.
I hate to be one that says.....but why do this with any embedded controller?
If I was going to do this....
Use a data acquisition board in a PC, one that had a fast counter input
(still using the hall effect sensor and magnet), depending on the speed of
the counters, you *might* need to condition it, ie....put a faster counter
on a breadboard then use the DAQ board to read it...
Ampere reading....several DVM's have serial interfaces, so you can monitor
both current and voltage with a pair of them
Someplace there was a web page with all the formulas (thought I booked it)
for converting HP to torque, etc.
You can calculate it based on current and voltage and knowing the standard
formulas. You can do all this in a nice program on the PC
But this is only how I would approach it. If you do it all in some sort of
embedded control chip, gotta worry about both hardware and software.
We (in amateur robotics roles) wanted to characterise surplus/UNK
motors, and came up with the following scheme which we brought
to the 'duct-tape'-' whatever else works' stage.
We mounted two identical (not necessary but convenient) motors
nose to nose with a coupler. They rested between two adjustable
rails (for a range of motor sizes). The motor-under-test ( "M.U.T."?)
was clamped to the rails (radiator hose clamps) the 'load' motor
could turn (more or less) freely but was attached to a bar which
extended radially to the side, from which we could hang weights.
There was a 'hard' limit on the bar at near horizontal, to prevent
propelering. In use we loaded the load motor with a resistive
load (big pot., light bulbs as appropriate) hung a weight on the bar
straight down and ran this; measuring R.P.M., input current/voltage
and measured the angle of the load bar (for torque). This was
simple, cheap, "exciting" at times, and had the advantage of
measuring torque independent of load-motor electrical properties.
The simple measurements we could make with this crude equipment
'made sense'. I don't think I would want to get 'this' (jury-)rig up to
what seems to be your speed/power range. But 1/8 H.P. dosn't require
a blockhouse either. But don;t forget the bar rotation stop, with
maybe an integral 'kill' switch.
Horsepower = (some const.) X Torque X R.P.M. ;dep. on units
Ourr next steps were to make a better mechanical system and
less junk box instrumentation. One thing was to measure the
torque ( proportional to sin (angle from vertical)) with a calibrated
pot. and servo the electrical load to control the angle using something
like a LM350 (with power xsister) based variable power (sink) supply..
We wanted to use a fish-scale to measure the torque but didn't
have an 'honest' one <G.>.
But we went on to other things. It would be interesting to hear
your solution. We wanted: cheap, and adaptable to a large range of
DC motors, size, power, speed.
> Hello all.
>
> I have been asked by a co-worker if this would be difficult to build.
>
> What we are looking to do is make a d.c. motor test machine. It needs to
> do just a few things.
>
> 1. Test the rpm. No less than 10,500 RPM
> 2. Test the Amperes being drawn at that speed No More than 6.2 Amps.
> 3. Torque it can handle.
> 4. Horse Power of motor. no more than 1/8 H.P.
>
> That's really about it.
>
> As far as RPM goes I thought about using a small magnet and a hall
> sensor. Let it sample for say 5 sec. the calculate it out. As for the
> amps. A simple amp meter would work. Is there a way to read the amps and
> then print it out or display a report ?
>
> Measure Torque ??
>
> H.P. can be done with the amount of watts that it draws. 1H.P. = 745
> watts (I think)
>
> Any suggestions on which pic to use? Or anything else I might need to
> look at?
>
> Please remember I'm just a hobbyist. Have only made a few simple things.
> But I would like to figure something out. If noting more than just to
> have a challenging project.
>
> Thanks..
>
> Jeff
<<
H.P. can be done with the amount of watts that it draws. 1H.P. = 745
watts (I think)
>>
That is a strictly theoretical approach to HP, which is a function of torque
and time, You need to determine true torque at a specified RPM to determine
HP. Could be done with some form of strain guage.
Tracey
Need to know more about what you're really measuring.
> What we are looking to do is make a d.c. motor test machine. It needs to
> do just a few things.
>
> 1. Test the rpm. No less than 10,500 RPM
I take it this is a pre-install test of a small DC wound field motor,
since you mention 6.2 amps.
Starrett or any number of other machine shop suppliers will sell you off the she
lf
mechanical tachometers.
> 2. Test the Amperes being drawn at that speed No More than 6.2 Amps.
fine - put a Simpson ammeter in the input line.
> 3. Torque it can handle.
I take it you want stall torque - go to the auto parts store and buy
a torque wrench and whatever collars and clamps you need to mount
it on the shaft. mount motor firmly on bench, and clamp torque wrench
in place. Think safety. Turn on motor and read off stall torque on wrench.
> 4. Horse Power of motor. no more than 1/8 H.P.
?????? This totally depends on the load. The horsepower
of a freely spinning motor is zero, as is the hp of a stalled motor.
No electronic devices needed here unless you're testing many, many of these,
in which case you have a robotics problem.
I can see where a device would be desirable and possibly cost effective.
If you mount the motor to a test fixture, go through a series of tests,
have the PIC collect the data and push a button to log the test results
automatically to say a database with motor serial number as the key. You
have a degree of automation and a way to quickly access the specs of any
motor in the database.
Eric
On Friday, July 16, 1999 6:18 PM, Anne Ogborn [SMTP:.....anniepooKILLspam.....NETMAGIC.NET]
wrote:
> Need to know more about what you're really measuring.
>
> > What we are looking to do is make a d.c. motor test machine. It needs
to
> > do just a few things.
> >
> > 1. Test the rpm. No less than 10,500 RPM
>
> I take it this is a pre-install test of a small DC wound field motor,
> since you mention 6.2 amps.
> Starrett or any number of other machine shop suppliers will sell you off
the shelf
> mechanical tachometers.
>
> > 2. Test the Amperes being drawn at that speed No More than 6.2 Amps.
> fine - put a Simpson ammeter in the input line.
>
> > 3. Torque it can handle.
> I take it you want stall torque - go to the auto parts store and buy
> a torque wrench and whatever collars and clamps you need to mount
> it on the shaft. mount motor firmly on bench, and clamp torque wrench
> in place. Think safety. Turn on motor and read off stall torque on
wrench.
>
> > 4. Horse Power of motor. no more than 1/8 H.P.
> ?????? This totally depends on the load. The horsepower
> of a freely spinning motor is zero, as is the hp of a stalled motor.
>
> No electronic devices needed here unless you're testing many, many of
these,
> in which case you have a robotics problem.
>
> --
> Anniepoo
> Need loco motors?
> http://www.idiom.com/~anniepoo/depot/motors.html
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