ARC200 Hydrofoil Testing

Discussion in 'ARC Universal Motor Drive' started by Jeremy Elliott, Jan 25, 2019.

  1. Jeremy Elliott

    Jeremy Elliott New Member

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    I have been luck enough to get an ARC200 to test on my electric hydrofoil! Currently it is pretty cold and gloomy in the UK and I am testing indoors with various motors to see how the drive handles them. The motors are as follows:

    - 6384 100KV outrunner (will make an attempt at a direct drive unit)
    - 5674 750KV inrunner (will run through a gearbox)
    - 56114 500KV inrunner (will be used with a jet drive)

    Thus far I have configured each motor for the drive and run some basic tests.

    The 100KV outrunner I have coated in corrosion X and tested in the bath tub. Here is a short video from the tests: https://scontent-lht6-1.cdninstagra...n.mp4?_nc_ht=scontent-lht6-1.cdninstagram.com

    Config wise I am running the drive in torque mode with a jitter start.

    I have found some weird results with the 500KV and 750KV motors though and have some questions I hope someone can answer...

    • In Torque mode with forward only, sometimes the motor will carry on spinning for ages by itself, is this normal behaviour?
    • In speed mode, the start up and slow down are very slow, how do I adjust the start up ramp and slow down ramp of the ESC?
    • How do I set a failsafe on the ESC (this might be in docs, but I haven't found it)?
    • On both the 500KV and 750KVI hear some strange ‘clicking’ noises when the motor is running, any idea what they could be?
    • The 750KV seems to get to a max speed and then slow down a little, is that the Max ERPM of the drive that is slowing it down a bit?
    If anyone has any question or tests they would like me to run, just let me know :)
     
  2. Tyler Christensen

    Tyler Christensen New Member

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    In Torque mode with forward only, sometimes the motor will carry on spinning for ages by itself, is this normal behaviour?

    Do you mean the motor keeps spinning even with a zero torque command? This is normal although fixable. What's probably going on is there are slight current offset biases in the measurement, so when you command 0A, it might still be providing a few amps of torque due to sensor offsets. This means that if the prop were under water, it'd most likely stop or slow down with a 0A command for this configuration. To make this problem go away or get much better, if you make the "Current Command Offset" parameter in the A. Control section a higher negative number (default is -0.15), it'll be more inclined to stop for a 0A current command.

    In speed mode, the start up and slow down are very slow, how do I adjust the start up ramp and slow down ramp of the ESC?

    This is setup with the "Slew Up" and "Slew Down" parameters in the H. RPM Loop section. Defaults are very low to make autotune a gentle and reliable process but you can set these much higher (although as you go up, speed and current loop tuning become more and more important, at some point you may find an instability).

    How do I set a failsafe on the ESC (this might be in docs, but I haven't found it)?

    The failsafe is not configurable. If you're using PWM control, then if the cable gets unplugged or PWM signal disappears, in speed mode it commands 0RPM (rapid stop) or in torque mode it commands 0A (no torque). If you're using analog control, the failsafe ensures that the signal is internally pulled down, so whatever a 0V analog signal does will be the failsafe result. Make sure you are running the latest firmware, there was a bug in earlier firmwares that made PWM failsafe ineffective. (Firmware update is here: https://freeflysystems.atlassian.net/wiki/spaces/FRP/pages/269320215/Arc200+Firmware+Updates)

    On both the 500KV and 750KVI hear some strange ‘clicking’ noises when the motor is running, any idea what they could be?

    Can you post a video of this? I can't tell you from that description but may be able to from a video. I was unable to view your video link (it says "URL signature expired").

    The 750KV seems to get to a max speed and then slow down a little, is that the Max ERPM of the drive that is slowing it down a bit?

    Arc200 has no enforced max ERPM. If you quickly accelerate the motor, it is normal for the max speed to overshoot a little (usually for a half a second or so). This is just due to the control dynamics of the current loops, there is brief field weakening which makes the speed go a tiny bit higher than is possible in steady-state. This is generally nothing to worry about, if you post a video of that too I can confirm that's what's going on.
     
  3. Jeremy Elliott

    Jeremy Elliott New Member

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    I have upgraded to the latest 1.18 firmware, however the failsafe is still not working. If I switch off my TX or if there is a signal loss, the ESC goes to full throttle. This is a major problem!
     
  4. Tyler Christensen

    Tyler Christensen New Member

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    Can you post your configuration file so I can take a look at it? Also just to be 100% sure, can you actually unplug the receiver from the motor drive while it's running rather than switch off the TX? I think some of those receivers have programmable fail-safes so it might be going to a high-PWM failsafe which would need to be changed to a low-PWM failsafe to match up to Arc200's expectation.
     
  5. Jeremy Elliott

    Jeremy Elliott New Member

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    It appears that even though the failsafe was working on a different ESC, I did need to reset it for the ARC200. I managed to get it working properly thanks Tyler.

    Now I need to get onto making the other video's with the other motors for you to take a look at.
     
  6. Jeremy Elliott

    Jeremy Elliott New Member

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    Finally got the time to get a video.

    - You can hear some strange scratching noises, not too sure what it is. Motor bearings are fine.
    - When the motor is running full speed, sometimes it takes a while to register that the throttle has been dropped back down to nothing.
    - You can also hear that the motor makes a weird noise when at full throttle sometimes.
     
  7. Tyler Christensen

    Tyler Christensen New Member

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    There seem to be two sounds there. The one where it's sort of a weird tone wobbling in and out every few seconds is normal for Arc200 on certain motors and is just part of the operation of the control loop (it's usually much quieter than this, but certain motors get louder on that like in this video). The much louder sound that is more like a vibration sound I'm not quite as sure on. It is possible for a motor to have resonances even with pretty good tight bearings. If it's really not the motor, my next thing to look at would be the current loop as that's about the only thing with a high enough bandwidth to possibly make a high frequency vibration. Try the various selections in the Current Loop Tuning Wizard making sure to click Run before Save Results to actually run the tune math. That vibration noise may also improve when there's mechanical damping through the load of a prop in water.

    As for the throttle having delay, this is speed mode correct? If so I think what's going on is let's say the motor's max speed given the power supply voltage is 5,000RPM, but the drive is configured for a max speed of 10,000RPM. It seems you have a fairly slow speed slew-rate, let's say it's 2,500RPM/s. In that case, the drive's internal speed-command will ramp up to 10,000RPM while the motor is only spinning 5,000RPM due to voltage limitations. When you then zero the throttle, it takes 2 seconds for the internal command to get down to 5,000RPM again due to the slew rate limit, during which point you won't be noticing anything changing. The real fix here would then be to reduce the drive's max command RPM to match what the motor is actually capable of on the supply voltage so that the internal command doesn't saturate. You also probably wouldn't really notice this if the slew rate was higher since the delay would be much shorter, although that would just mask the issue in reality.
     
  8. Jeremy Elliott

    Jeremy Elliott New Member

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    Thanks for the response @Tyler Christensen
    Which RPM limit do I need to change in the config. The max RPM my motor should hit is around 37800 at 50.4V.
     
    #8 Jeremy Elliott, Feb 15, 2019
    Last edited: Feb 15, 2019
  9. Tyler Christensen

    Tyler Christensen New Member

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    When you're running it at full throttle as currently configured, go to the Telemetry tab and look at the "Speed" field. Take that number (which is the actual measured speed of the motor, there's not enough voltage to make it spin any faster) and go to the configuration tab, section H. RPM Loop, enter that as the Forward and Reverse RPM Command Max then send that config. See if that makes your problem go away on the throttle delay (I'm guessing the parameters for RPM command maxes are quite a bit higher than the actual measured max speed you will observe).
     
  10. Jeremy Elliott

    Jeremy Elliott New Member

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    Thanks @Tyler Christensen that solved it! I can't wait to get my board back now so that I can put it all together and test it on the water!
     
  11. Jeremy Elliott

    Jeremy Elliott New Member

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    Been a while so I thought I'd upload a few pictures...

    First the board:
    20190627_094946.jpg 20190627_095019.jpg 20190627_094322.jpg 20190627_094347.jpg

    The ARC200 is attached to this watercooled heatsink:
    239bf6464000c041d9c7925b0688121a38493e2a.jpeg
     

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