Connecting Blower to Flight Computer AUX PWM Port

I’m trying to connect a blower to one of the auxiliary PWM ports on CUAV 5+. I have the electrical connections shown below. This blower works fine when the control voltage input and ground are connected to a function generator. When I try to switch the setup over to CUAV, the ground wire keeps getting shorted, and I’m not sure what the cause is. Initially thought it could be due to poor crimping on the connector resulting in high contact resistance, but I tried a few diff connectors and am still getting the same result. Anyone have any thoughts here? Possible that I’m missing something obvious.

CUAV Setup:

Function Generator Setup:

Blower Data Sheet:

What do you mean “keeps getting shorted”

Looking at the datasheet, the control input is a 1-5 Volts you need to set the IO pin, A6 in your case, to GPIO and then you should be able to turn the fan ON and OFF only. If you need a variable speed you will need the PWM output from the PX4 to be converted to voltage using a PWM to voltage ‘adapter’

Edit: You could change the controller to an ESC as the blower motor is a three phase motor.

Even so as @geofrancis mentioned I don’t know what you mean by “keeps getting shorted”

2022-06-30 11_43_32-コパルTF037-TF029シリーズ-英01

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@geofrancis and @myozone Shorting clarification: After the connection is made, the wire sparks, heats up and melts.

are you powering the pixhawk from the same power source as the fan?

My planned flight configuration is as follows: Fan power tees off from one of the 22V batteries, while 5V is supplied to Pixhawk via the 44V source and UBEC is used to step down the voltage.

For the troubleshooting config, Pixhawk is also connected to computer via USB.

Power the blower from the other battery. It has the common ground. The one your using has a ground at +22v relative to the flight controller

You should really use a step down regulator to power it, running it off one half of your battery like that will cause battery cell imbalance problems and your lightly to run out of power unexpectedly.

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I see the problem. You’ve probably blown your FC. Your ground to the blower and FC’s ground are 22v apart !

You beat me to it @geofrancis :grinning:


@geofrancis & @myozone Thanks for the input, that makes sense. Looking back on my config, I actually did have the blower connected to the first battery (I just had it swapped on the schematic above). Pixhawk was also connected to the computer via USB which may have been the issue since common ground between computer and battery is not shared - does that seem reasonable? (that being said it is unclear to me in this case whether pixhawk is powered by USB or batteries)

@geofrancis - Good point on cell imbalance issues, I will plan on stepping down from the 44V supply - I originally wanted to avoid using a dc-dc converter since it’s heavy and reduces vehicle performance.

@myozone thanks for the input. I ended up going with a passive RC filter instead to reduce additional power consumption

Glad you mentioned an RC filter, that’s why I described it as an ‘adapter’ rather go down the road of explaining it :thinking: :grinning: