Hi everyone,
Not sure where else this discussion fits in. Since this category seems to be the closest match I post it here.
For a long time I've had issues with my MT339 GPS getting locks at all or within reasonable time. I'm fairly confident I traced it back to a noisy switch-mode BEC that is part of the ESC I'm using (from a well-known company that usually makes quality products). This ESC has survived some crashes so although it appears to be fully functional this may have caused it.
In any case.. plenty of people report GPS and other sensor related issues (sonar, magnetometer, etc.). See also this blog post here. So I would like to discuss whether it would make sense to have a dedicated power supply powering APM and the sensors (possibly servos, too). If so, then I think it could make sense for 3DR to offer one at a reasonable price (personally, I believe most RC BEC's are overpriced) so that people can just get it when ordering their other drone stuff. Also, it would be possible to verify directly whether this power supply causes problems with sensitive sensors such as GPS. As far as I know, some FPV guys only use custom BEC's for avoiding noise on the video channel.
It seems that I was able to solve my GPS issues by powering the GPS from its own supply (cheapo 5V linear regulator and a bunch of capacitors for suppressing noise). But I would much more prefer a more integrated solution. Also, although I'm an electronics noob, I understand that switch-mode regulators are more efficient and don't have the issue of overheating. Besides, one would need a regulator that can provide more than 1A I guess (particularly if servos are powered, too).
What do you think?
Cheers, Andre
Replies
How about something like this.
Thanks for the pointers everyone. Guess I'll have a closer look at the Turnigy BEC. At least it claims to have some sort of RF noise reduction. More generally, I like Andreas' idea of combining the battery monitor (including current sensor) with a BEC (for the copter fans that could be all part of the PDB). That would mean the same number of connections as currently but with the benefit of not being at the mercy of some noisy ESC.
@John: the MediaTek GPS has it's own regulator on the adapter board? At least can't see any caps there.
The APM board has a dedicated linear 3.3v regulator for sensors. So unless the 5V BEC is VERY noisy, the 3.3v regulator should even it out.
The Turnigy 3A BEC was mentioned. It is a switched BEC and has good enough performance for most tasks (when used with properly designed circuits). And a reasonable price. I use it all the time.
There are plenty of single-package DC-DC converters, which are very stable and clean with little to no external components at all.
I'd recommend using one of those because they are simple, a lot cheaper and almost certainly higher quality than a commercial "BEC" - you're right in thinking they are stupendously expensive and not all that good.
For example, this 1.5A module is £5.68 from Farnell, ($4.69 from Newark, bastards!) and is a drop-in replacement for a 7805, needs no external components and has a ripple of 17-34mV supplying 5V@1.6A from 7V to 36V supply.
The step responses look pretty good as well.
- That's with no external components at all, adding a reservoir capacitor on the output will improve them.
There are plenty of others that may be better, I just took a glance at the cheap wide-voltage range.
Absolutely agree, and I would spend up to perhaps $25 or $30 for a good BEC.
I purchased a Castle BEC (rated at 10A - allegedly) and also a 3A rated turnigy. One is a "switched" BEC and the other a UBEC, whatever the U stands for (I have no idea). I am not sure what the difference is and which is best for say video or sonar.
Either way, it makes my life easier to have a separate feed for the electronics and it seems to be necessary for additional "accessories".
In fact I would go a bit further and add: A complex quad might need a PDB, a BEC and an Attopilot battery monitor. All three connect to the primary power feed.That's a big blob of solder (or three).
Would it make any sense to combine all three functions (PDB, good BEC and battery monitor) in a single board? Perhaps a PDB+ or PDB-Pro?
Or sell all three as a package?
If you add it up: BEC - $25, PDB - $15 and battery monitor $20 = $60.
I would buy it