I've noticed a few posts claiming sonar noise can be reduced by shielding the cable. What's the consensus on how to do this? I've seen some posts saying the ground the shielding at both ends, others just one. I'd appreciate any thoughts/feedback.
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Gave in and pretty much re-wired the whole quad. Twisted all of the power wires and just cleaned out all of the routing in general. I have a pretty much perfect sonar signal now though!
I would like to track down the source of this noise anyway. If it's enough to affect the sonar, surely it will be affecting other components in the system.
For example my minimOSD has a crosshair that flashes in the middle of the screen when it shouldn't, and also my GPS takes forever to get a 3d fix. Sometimes not even in 10 mins with the quad armed with no obstructions. My LED strips also behave weirdly when in show_leds mode too. Not sure if these are related at all or just red herrings, but I'm not sure where to start really.
Thanks. I put the capacitor/resistor in today, and flying it gently low around my backyard this evening it seems to be holding altitude perfectly with no noise on the sonar. I took it to the park afterwards and flew a bit more aggressively, but looks like I still got a bit of noise on it there. I still suspect I have some electrical noise somewhere in the system so will have to figure out how to track it down or prove whether I actually do or not. Here are the logs from today anyway.
backyard:
park:
I ended up going with a 10 ohm resistor and 16v 100uF capacitor.
Bit of an update on this.. I just reconnected the APM to be powered from the ESC's 5v feed, and powered the sonar directly from the UBEC, and it seems to have pretty much sorted this out. There are a few spikes like before around line 1000, but it seemed to hold its altitude well.
So this makes me wonder what is going on? The UBECs input leads are connected straight where the lipo wires connect to the PDB, and the outputs are to the +5v and gnd on the sonar. The signal wire connects to the usual place on the APM. This wouldn't create a ground loop or anything would it?
I'm having a bunch of issues getting my sonar to work correctly. I have the XL-MB0, and it seems my sonar pretty much works for a few seconds, before spiking wildly. I've been through all of the sonar threads i can find and tried all of the fixes, but it still seems to be acting up.
I have:
*Disconnected the 5v input to the APM from one of the ESCs and replaced it with a UBEC.
*Rerouted the sonar cable to be clear of any ESC wires. The closest it comes is about 30mm, and only passes perpendicular.
*Replaced the sonar cable with a shielded one that is only grounded at the APM side.
*pot the sonar on a dampened extended mount which lowers it a couple of inches underneath so there should be no legs or bits in the field of view.
Does anyone have any ideas what could be going on? I suspect there's some electrical noise somewhere in the system, but I'm not too sure how to isolate it. I tried unplugging my video tx thinking that might be the cause, but it was exactly the same so I'm pretty sure that's not it..
Some logs:
With UBEC but before shielded cable
After shielded cable and reposition/reroute:
This was in alt hold mode. It initially held it's altitude of about 1M as you can see with the nice solid line, before it started to climb and the sonar values started to start going all over the place.
Help!
I was recommended a 10 Ohm resistor for the MB1200 XL-MaxSonar-EZ0 by Scott from Maxbotix, by the way. I soldered a filter on my sonar yesterday but I am still getting unreliable signal some of the time. The hunt for the solution continues... my sonar is about 12 cm from the nearest ESCs, (between two of them next to the hub, ESCs are on the arms). Since my sonar noise is seemingly intermittent in nature, it makes me suspect noise - either RFI or maybe even mechanical coupling of physical vibrations to the sensor via the mounting. Next up: shielding the module itself to prevent RFI from possibly entering the sonar itself, since the cable is already shielded.
The Maxbotix recommended filter has been discussed before and I tried it with both 10 ohms and 100 ohms with no help. Moving the sonar was the biggest help and I am not using the filter now with really clean sonar data on a standard quad.
http://diydrones.com/xn/detail/705844:Comment:468454
I may get a lot of negative feed back on this, but I have been wrapping my sonar cables in carbon fabric tissue. In lay terms there is reflective shielding, absorbent shielding, and a combination of both. After doing a little research into the matter I decided to go out on a limb and wrap my sonar cables five times in carbon fiber tissue to absorb any excess EMI/RFI. If anything I am getting far better sonar readings and holds than before wrapping. Spray the carbon tissue wrapped cable with Plasti Dip rubber coating for a flexible hold, or similar product. I have quite a few flights with this arrangement with no adverse effects in sonar performance. I will be posting some flight videos using this method later today or tomorrow to show how effective it has been.
There are two items (related to maxbotix sonar performance) besides shielding that I do not recall having seen discussed, and I keep forgetting to mention them. Both direct from the vendor.
First is a performance tuning recommendation for analog input use:
http://www.maxbotix.com/tutorials.htm#How_can_I_get_the_best_possib...
The second, more significant than the first, is on the same page, at the very bottom (no anchor) entitled "UAV and Mobile Robotic Users (Simple fix for when electrical noise interferes with the MaxSonar sensors.)"
I've been working with a balance bot,
and I think generally, many of these servo + electronics + radio + sensor designs get the power distribution quite wrong.
Instead of relying on the BEC (or ESC), They should (IMO) have several independent 5v regulators. Particularly the servos could be separated from the thinking bits, but generally, lots of local regulators would be an improvement - basic power could be higher and rougher (6v), and boards could step that down as needed, while using the straight line for servos.
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