M4 motor runs when powered on.

Info and discussion about the autonomous Micro FC, suitable for nanos, micros and mini multirotors

M4 motor runs when powered on.

Postby Mullet » Mon Apr 20, 2015 5:16 am

After doing some trouble shooting with regard to an issue with motor saturation and as a result replacing props -- nothing out of the ordinary. Now my A motor constantly spins when powered on. When I power off the M4 the motor still spins a lot slower, but it's moving. Could I have somehow burned out one of my FETs? Seems like a short or something that would cause this. The weird thing is I didn't do anything special. Good times.
Mullet
 
Posts: 181
Joined: Sun Dec 28, 2014 5:56 am
Location: Fairfield County Connecticut

Re: M4 motor runs when powered on.

Postby LPR » Mon Apr 20, 2015 2:54 pm

The only I know of one way to have a motor keep spinning after switching the M4 off and that is to have power wire put power directly into the motor. Look carefully at the connection were you soldered on the power wires.

Please don't ask how I know this.

Larry
LPR
 
Posts: 1323
Joined: Tue Jun 26, 2012 1:29 pm
Location: MN, USA

Re: M4 motor runs when powered on.

Postby Mullet » Mon Apr 20, 2015 10:43 pm

Like I said the M4 was functioning normally. I'm a bit perplexed. Looking at the M4's FETs they look to be labelled "WM4 47". I could try applying power via battery and measuring with a digital multi-meter to gnd. Any idea what voltage I should see? I'm supposing around 3.7 to 4v for a fully charged battery on the input side and nothing on output for M2-M4. M1 possibly is sending voltage no matter what.
Mullet
 
Posts: 181
Joined: Sun Dec 28, 2014 5:56 am
Location: Fairfield County Connecticut

Re: M4 motor runs when powered on.

Postby Mullet » Mon Apr 20, 2015 11:43 pm

Ok... So when I measure from GND to Red Pin with battery on I get around 3.75v for every motor. When I measure on the single pin side of the SOT 3 package next to motors I get around .5v-.6v on M2-M4. I get nothing on M1. I'm thinking that SOT 3 package is the culprit. I can resolder on a new one if I only knew the part # at mouser, etc. I can steal one from a legit Ladybird FC, but don't know if it would be completely compatible.
Mullet
 
Posts: 181
Joined: Sun Dec 28, 2014 5:56 am
Location: Fairfield County Connecticut

Re: M4 motor runs when powered on.

Postby Kisssys » Tue Apr 21, 2015 12:18 am

568-2354-1-ND is the Digikey number for the FET, the Ladybird one would probably work. If you accidentally short the motor pins you will blow the fet.

Cheers
Steve
Last edited by Kisssys on Tue Apr 21, 2015 2:12 pm, edited 1 time in total.
Steve
Kisssys
Kisssys
 
Posts: 1340
Joined: Sat Jun 23, 2012 9:23 pm

Re: M4 motor runs when powered on.

Postby Mullet » Tue Apr 21, 2015 3:47 am

You sure that's the right part? That looks like a 6 pin device vs. 3 pin device that I was expecting.

Would this be the right part?

DMN2004KDIDKR-ND
Mullet
 
Posts: 181
Joined: Sun Dec 28, 2014 5:56 am
Location: Fairfield County Connecticut

Re: M4 motor runs when powered on.

Postby Kisssys » Tue Apr 21, 2015 2:15 pm

Sorry bad cut and paste. 568-2354-1-ND. It was on the discontinue list, Jussi might have a few or just put on the Ladybird part.
Steve
Kisssys
Kisssys
 
Posts: 1340
Joined: Sat Jun 23, 2012 9:23 pm

Re: M4 motor runs when powered on.

Postby Mullet » Tue Apr 21, 2015 11:43 pm

Steve,

Thanks for the part. It looks like Mouser still has 'em in stock. I might grab a few diodes as well. Any idea if this is the part # I'm looking for...

1N4148WSFSCT-ND

I'll most likely use a hot air station to do the job. While I'm at it, I'm thinking that using some solder paste and kapton tape (to protect the picoblade recepticle) will help in such a tight space.
Mullet
 
Posts: 181
Joined: Sun Dec 28, 2014 5:56 am
Location: Fairfield County Connecticut

Re: M4 motor runs when powered on.

Postby Kisssys » Wed Apr 22, 2015 2:54 am

The Diode is BAT54HT1GCT-ND. The key to working on the M4 is not counting on normal vision. Magnification is a must.

Cheers
Steve
Steve
Kisssys
Kisssys
 
Posts: 1340
Joined: Sat Jun 23, 2012 9:23 pm

Re: M4 motor runs when powered on.

Postby Mullet » Tue Apr 28, 2015 3:50 pm

Used good magnification. Solder paste, a hot air re-work station, and kapton tape and had success with replacing the known faulty (leaky) mosfet. The only caveat was that there was a tight fit between the kapton tape, the molex picoblade header (wire housing), and the area of re-work. As a result, I ended up melting two picoblade headers. Luckily, I had replacements available just in case.

All said, I now have a working M4 again.

Due to the fact that these mosfets are end-of-life, it looks like this might be a suitable replacement...
771-PMV20XNER. Not sure if the lesser power dissapation and slower fall time would make much of a difference. They can handle more current though...
Mullet
 
Posts: 181
Joined: Sun Dec 28, 2014 5:56 am
Location: Fairfield County Connecticut

Next

Return to AutoQuad M4 Micro Controller

Who is online

Users browsing this forum: No registered users and 22 guests

cron