(Helicopter) governor in MWii (instead of in ESC)

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Hamburger
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(Helicopter) governor in MWii (instead of in ESC)

Post by Hamburger »

Hi,
I have been debating with PatrikE the implementation of governor mode in MWii. This is typically used in CP helicopters to keep a constant head speed under varying loads (like increased blade angles = pitch). The same approach could be used to correct load changes from flight situations for other copter types. A TRI's rotating yaw motor would require an increase of throttle to compensate for tilted direction of thrust, possibly proportional to angle?

Patrik pointed out that the real thing would be to monitor the head rpm - (use sensored motor or ) typically attach a magnet to the rotating head and use a hall sensor to measure true head rpm.

My idea was to do a poor man's governor implementation in software only. In MWii we have info like yaw, throttle and collective pitch input from the tx-rx; so it would be possible to monitor for changes in yaw and collective pitch input and apply controlled temporary correction to the throttle output signal going to the esc. User increases collective pitch in his tx for copter to rise -> temporarily increase throttle output to keep rpm high.
Also we can monitor battery voltage and observe short term changes - another indicator for increased load. That would allow to run the motor at a constant throttle curve in the tx and have MWii induce short term increases when neccessary.

Not sure if another PID controller would do it best?
- observe collective pitch
- proportional to change of collective pitch add correction to throttle output
- decay that correction over time back to zero

Comments?

copterrichie
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Re: (Helicopter) governor in MWii (instead of in ESC)

Post by copterrichie »

Retrieving RPM information from the ESCs is one of my pet peeves. The information is there, just need to get it out. If we are unable to retrieve the information directly from the ESCs, I'd hoped to give this circuit a try one day.

bldc_rpm_sensor.gif
(6.07 KiB) Not downloaded yet

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Re: (Helicopter) governor in MWii (instead of in ESC)

Post by Hamburger »

for any given ESC+motor combo, I thought the rpm was directly tied to the input pwm throttle signal (provided the motor was strong enough to drive the load).
That is why when under constant pwm signal you increase collective pitch, then you can hear the motor temporarily whine under the load increase (what they call 'bog down'?) before it gets the rpm up again to the nominal value.

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Re: (Helicopter) governor in MWii (instead of in ESC)

Post by Hamburger »

first implementation works on the bench.
debug1 = collective pitch
debug2 = governor throttle addon
debug3 = throttle
debug4 = resulting throttle (2+3) output

Here is a simple graph taken with the GUI. Basically I arm, move throttle stick slowly all the way up (increase throttle and collective pitch signal), then back off some to about 70% stick range, then do quick pitch pumps.
proactive governor
proactive governor

this will require some tuning at the field - I have no experience with other governors, so I need input on both
- how much should the governor proportionally increase throttle
- how long should it take to decay the governed throttle back to the stick value?

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Re: (Helicopter) governor in MWii (instead of in ESC)

Post by copterrichie »

But the element that is being overlooked is, battery voltage. As the voltage of the battery decreases, the required PWM goes up.

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Re: (Helicopter) governor in MWii (instead of in ESC)

Post by Hamburger »

Right, but
1. MWii in general does work on the basis of pwm signals, not rpm
2. Mixing in rpm only for the governor could be misleading.

Experienced pilots will compensate for drained battery already by flying in higher signal range. .Having the governors portion added to the throttle being the single component dealing with boltage and rpm would be wrong.
Converting entire handling of throttle to rpm would take care of all this, maybe will try that later.

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Re: (Helicopter) governor in MWii (instead of in ESC)

Post by Hamburger »

copterrichie wrote:...battery voltage. As the voltage of the battery decreases, the required PWM goes up

hamburger wrote:Converting entire handling of throttle to rpm would take care of all this

I test flew a first implementation which does exactly that. With my large heli (325mm single blade length) it was scary as I was not feeling the drain and reduced power from the old aged battery over the 6 minutes period I was flying. Without crit.voltage&timer&capacity monitoring this would have resulted in a fine crash. While theory may provide enough reason to falsify this approach it seems to work not too bad in real life.

As a side effect, it makes failsafe.throttle indpendant from remaining battery voltage.

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