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Discussion: How Would You Roadtest the MagAlpha Angle Sensor Kit

rscasny

imageI usually provide the technical details and documentation on a roadtest page for people to look over at their leisure.

This material usually gives people ideas on how they would like to roadtest a product. But I think sometimes, it's good to actually talk about how one would roadtest a product, due to perhaps it's something new for many people, or it needs a little more background.

I think this angle sensor kit is one of those products.

When we decided to roadtest this kit, we initially provide the sensor and the communications board. But with only those things, the roadtester would have to mount the magnet and the sensor to the motor shaft. Seemed like heavy lifting, so the supplier came back with the kit that's on this page (right):

community.element14.com/.../mps_magnetic_angle_p

The sensor board is mounted to the end of the motor shaft already (as well as the magnet). The roadtester would need to hook it all up, connecto the Arduino board (not shown in the image at the right) and spin the motor.

But still, how do you actually test it.

More importantly, why is this sensor important to roadtest?

This clip from the sponsor's website pretty much explains it:

The ability to detect position or speed is a fundamental requirement in the control and monitoring of many mechanical systems. Slow speed position measurement in applications such as motorized actuators has historically used resistive potentiometers. In high-speed applications such as servo motors, optical encoders have typically been used. Though potentiometers are inexpensive, they suffer from the drawback of being a moving contact-based assembly, which brings the associated issues of mechanical contact wear and susceptibility to damage from external environmental factors including moisture and dirt ingress. Optical encoders offer high accuracy, but come at a higher price due to the complex nature of their construction. Engineers can solve this dilemma by using contactless rotary magnetic angle sensors that implement Hall-effect sensing.

This page goes into detail about the angle sensor, specifically about its SpinAxis technique: www.monolithicpower.com/.../introduction-to-the-magalpha-magnetic-angle-sensor-family

The kit we are providing to the roadtester is a motor control kit. But we would like to get roadtesters to take a closer look at the angle sensor. Run some tests, play with it, and give some feedback or thoughts about it.

So, that's my backgrounder.

What do you think?

How would you test the sensor?

Even if you don't have the time to take on this roadtest, I'd appreciate your input. It would benefit those members who are thinking about applying.

Thanks.

Randall Scasny
RoadTest Program Manager

  • Hi Randall,

    That sensor has incredibly high granularity for position sensing, and works to a very good speed (60,000 RPM) and so the uses for it could span across a lot of things that traditionally would have used more complicated set-ups like optical encoders. 

    It uses a very novel technique for sensing, that I've not seen before (it effectively spins the "sensor" inside the chip, through switching lots of mini-sensors arranged in a circle!).

    I'll give this some thought and come back to you, head needs to think on it : )

  • I would mount the sensor to one of the stepper motors on my 3D printer. That way one can test absolute accuracy of the positioning - zero it after homing on the axis, run a print, home again and the position should now be zero again. (you need to handle more than 360° revolutions, though). Although that is not checking how fast the sensor is, I think its quite stressfull for the sensor.

  • This is an excellent motor kit, but if you look around your house there aren't many, if any, motors of this size, so there is no obvious need. However it is a very flexible kit and can do many things, especially where smart control is useful. Here are a few suggestions:

    - robot steering motor or drive motor

    - open and close windows, curtains, doors, shutters under voice control or light activated etc.

    - voice controlled fan

    - automatic "follow me" microphone

    - motorized camera positioner for smooth action video

    - BBQ rotisserie - speed proportional to surface temperature

    - positioning stage for any mechanism

    - control for sail position on a model boat

  • For a RoadTest, I could see it being used in a persistence of vision POV project.

    In real life, like  also mentioned - it would make sense for things like smart curtain opener type applications where it needs to know how much movement the motor has made. But it might be overkill for that sort of thing.

    Also Mars Rover kind of use - autonomous little robotic vehicles might use it to keep track of distance moved, or maybe to compare actual distance moved to how far the motor thinks it should have moved, to detect wheel slip.

  • I have revisited the RoadTest page for this product a few times trying to create a testing methodology. I have yet to find a project I could do. After reading your post I thought of a piece of equipment called a rotating beam ceilometer. It was a vacuum tube transmitter and receiver used at airports to measure cloud ceiling. I thought there is a use for angular measurement.

    image

    The transmitter had two three-foot diameter parabolic glass mirrors with a modulated light source in the middle. As the mirrors rotated the modulated light would be transmitted into the sky. A receiver was located at a known distance from the transmitter. It would receive the modulated light reflected from the cloud base. Using trigonometry you have one angle and one side of a right-angle triangle, you can calculate the other sides. Thus the cloud height at the end of the airport runway could be determined.

    My first technology career involved doing maintenance on equipment.  The transmitter had a number of dangers. The mirrors not only reflected light, but they also absorbed it if it was pointed at the sun. It was capable of burning a person. I put my hand in front of the mirror to prove my theory and discovered the facts real fast! These were big mirrors so the motor to rotate them had a lot of torque. Lockouts had to be in place to prevent the motors from engaging when you were inside the housing cleaning the mirrors or changing the halogen lamps.

    The distance between the transmitter and receiver was 50-100ft I recall. I visited the receiver one night on a maintenance callout and stepped on a grouse. Scared the crap out of me. The equipment was located at the end of the airport runway very close to the woods. Black bears visited the area often because of the blueberries that were abundant. No lights were permitted in the area to reduce interference in the equipment. Night visits with bear warnings were common.

    The equipment was later replaced with a unit that was a five-foot tube one-foot ft in diameter that housed a laser. It used the same trig math to determine height with a much smaller footprint and more accuracy.

    The motor kit for this road test could provide that angular measurement for the rotating light source. It would replace all the commutators and mechanics used to determine the angle of the mirrors used some fifty years ago.

  • Simply coming from a Data Center background early warning from pumps, fans, and mechanical speeds of various components can be lacking in BMS applications. A motor that controls a fan can be monitored but this might possibly monitor the pulley on a belt possibly that ignores the speed of the motor with a failing fan belt controlling air flow as an early detector of failure. A pump motor can have power but not to detect if its rotating. Being able to add remote monitoring of its functions would greatly increase response time to failure? 

  • in reply to ntewinkel

    Wow - I had the same ideas and saw you had submitted them before me. Great minds think alike :-) 

  • in reply to colporteur

    Your diagram inspired me to think 3 of these could be used on a small satellite tracking antenna, or for tracking an antenna pointed at the international space station, or some type of telescope you'd like to stay fixed on a certain sky position inside the horizons.

  • in reply to robogary

    i thought tracking a solar panel might work also.

  • From the sounds of this - Tesla uses an angular sensor on the Model S door handles. It uses them for position feedback to 'present' the handles and uses them to detect when someone has walked up to the car and pressed on the handles to get them to open. Would be cool to test a system like that.