Hello Guest it is July 16, 2019, 11:14:46 PM

Author Topic: Building a stepper motor dyno  (Read 4582 times)

0 Members and 1 Guest are viewing this topic.

Offline Jeff_Birt

*
  •  1,107 1,107
    • View Profile
    • Soigeneris
Building a stepper motor dyno
« on: October 21, 2012, 09:41:38 PM »
I've been trying to stress the importance of choosing the right stepper motor for the job for years now. This runs contrary to the 'bigger-is-better' idea that is so popular among hobbyist. I often point folks toward stepper motor torque curves but as these are all done by different manufacturers, with different stepper drives, etc it makes it hard to try and compare two different motors. (And sometimes I'm not sure how accurate some of these torque curves are.)

In an effort to have more reliable data to work with I decided to build my own stepper motor dyno for testing. I just posted the first blog entry today that covers the build: http://www.soigeneris.com/Blog/Default.aspx Follow along with the process and let me know what you think.
Happy machining , Jeff Birt
 

Offline RICH

*
  • *
  •  7,341 7,341
    • View Profile
Re: Building a stepper motor dyno
« Reply #1 on: October 21, 2012, 10:11:17 PM »
Should be a very interesting build and topic and will visit over time to see how it all turns out.

RICH
Re: Building a stepper motor dyno
« Reply #2 on: October 22, 2012, 12:19:54 PM »
The exact problem I was faced with for the Bridgeport, and will again soon with the lathe hopefully....just what size stepper do you need???!!!

Offline Jeff_Birt

*
  •  1,107 1,107
    • View Profile
    • Soigeneris
Re: Building a stepper motor dyno
« Reply #3 on: October 22, 2012, 12:27:42 PM »
I posted the second installment a few hours ago. It covers modifying the motor to drive the encoder.

@EJParrot - The choice of drive and drive voltage also plays a big role. That is another thing I'm hoping to shed some light on: How does the same stepper motor, at the same drive voltage perform with different drives.
Happy machining , Jeff Birt
 

Offline BR549

*
  •  6,874 6,874
    • View Profile
Re: Building a stepper motor dyno
« Reply #4 on: October 24, 2012, 05:59:40 PM »
HIYA Jeff, I saw your blog, interesting.  I have built a FEW (;-) dyno's over the years, Load brake(water,Hydraulic,Mechanical), inertial, eddy current, etc

It appears you will need to have many accurate resistors on hand to vary the load??

IF you are just looking for a torque/rpm curve you may want to consider an inertial dyno. You simply hook the motor to the input shaft and spin the motor  to full rpm against the inertial load of the flywheel. Torque is a function of Accelleration rate and inertial value of the wheel. Easy to calculate.

The inouts need would be the inertial value of the wheel AND a simple tachometer or better an encoder.

NOW it would NOT do steady state testing as the wheel HAS to be accellerating to obtain a torque value.

For steady state test you may want to consider an eddy current style OR a load brake based on a DC motor with field input to produce load. The motor is floated from both ends on bearings and a load cylinder offset from the motor centerline is used to measure force. You can vary the motor brake LOAD by varying the Voltage to the field input.  You still run a large resistor bank to absorb the output from the motor running in generator mode. 

Again easy to see torque as it is direct readout from the load cylinder reading and the RPM is from a simple  encoder.

Just a thought, (;-) TP

Offline Jeff_Birt

*
  •  1,107 1,107
    • View Profile
    • Soigeneris
Re: Building a stepper motor dyno
« Reply #5 on: October 25, 2012, 11:20:22 AM »
As the saying goes, "there are many ways to skin a cat." Using a DCPM motor allows for a conceptually simple project that is easy for most folks to understand the theory of operation. Since I wanted to share the project with others this was a good place to start. As you say using a motor with field windings rather than magnets would allow for easier control of the load presented. You can also just switch in resistance, and monitor the current. Measuring the current (and voltage) eliminates the need for precision resistors.

I built a similar dyno for the university here for a student that was studying how to diagnose problems with three phase motors. Since they do a lot of tours through the lab it was going to be in I used 100W light bulbs as a load and measured the current/voltage on the DC side (well on AC side as well for diagnostic purposes). Anyhow it is kind of neat to watch it go through a test cycle and see the lights turn on/off. It makes a good visual for tours as well :)
Happy machining , Jeff Birt