With the profusion of low-cost components available today, it's tempting to pick the cheapest one that looks like it will do the job and not stop to think too hard about how well it's going to work. After all, if it's for sale and other people are using it, it must be OK, right?

Consider this post by the respected DIY ESC developer Takao Shimizu, talking about a low cost controller available from a popular vendor:


The money quote:

But, when it's over the current (>2A), then the output voltage goes up to the input voltage(11.4V).

Read that carefully: if you overload the ESC (and 2A isn't that much of a load), your 5V supply suddenly becomes an 11.4V (or higher) supply. Think about how much you have invested in your receiver, servos, autopilot, GPS, OSD, camera(s), etc. Many (most) would be destroyed more or less instantly by a surge of that kind.

It's not just power supplies, though. Cheap servos are tempting too, but again they represent a single point of failure for your aircraft. If you're just building a foamie with an anticipated flying life of a few months, you might be willing to accept the occasional failure and early demise, but if you're flying several hundred dollars worth of gear, a few bucks more for decent servos is a much better investment.

Views: 221

Comment by Steve Oliver on August 30, 2010 at 6:09pm
Sounds like a good reason to use a separate battery for the APM and similar boards, good thing they included that solder jumper we can remove easily :)
Comment by Greg Fletcher on August 30, 2010 at 8:17pm
Good post Michael,
I feel the same way. Single point failure is an uncontrolled crash. Either fly a little foamie and accept it, or decide that "failure is not an option". Strive for perfection and achieve what you can or accept what you get :}
Comment by Ryan on August 30, 2010 at 8:22pm
I always us a separate 6V for my Rx
Comment by Jimmy P. on August 30, 2010 at 9:26pm
Ugh.. I desoldered it and the solder pads came off... and Sparkfun has been OOS for weeks.
Comment by Brett Glossop on August 31, 2010 at 12:15am
@Jimmy I found the same, but replaced with hookup wire. Required track tracing to good soldering spots (relatively far away from pads).
Hope that helps you.
Brett G

T3
Comment by Krzysztof Bosak on August 31, 2010 at 2:54am
Interesting that a lone-wolf ESC developer is an institution keeping the quality control, when all law regulators, product developers, merchants and even client's knowledge failed to diagnose. I think his knowledge will be lost in marketing noise no matter our efforts to spread the warning.

Developer
Comment by Michael Smith on August 31, 2010 at 8:49am
Krzysztof - If just a few folks stop and think twice about the gear they purchase, I'll be happy. This whole race to the bottom thing has been a mixed blessing for the hobby; more people flying more interesting things, but more of them falling out of the sky unexpectedly too.

Moderator
Comment by Sgt Ric on August 31, 2010 at 9:24am
I remember a recent video (I don't think through DIYDrones, maybe RCG) about someone flying a huge composite sailplane which crashed spectacularly... the post mortum was that they had used a cheap generic 30A ESC/BEC which burnt out.

A person can spend a year bldg a beautiful aircraft and spend thousands getting it ready and then save a few bucks on a generic part that can ruin everything in an instant.

Beware the weakest link, as they say
Comment by Chip on August 31, 2010 at 9:29am
I try to stick with name brands, even if it costs a little more you can generally rely on them. I have enough problems, I don't need a radio/esc/servo failure to throw off the troubleshooting process.
Comment by James F. on August 31, 2010 at 10:02am
I think if this type of thing happened enough no one would buy the cheap stuff. I'm sure this type of thing happens with name brands as well. It really comes down to risk %. Is 5%-10% more risk worth double the price? Unless someone knows the facts its hard to come up with a risk assesment. Maybe that is the best reason/excuse to have an AP system as back-up.

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