Dan Houldsworth
  • Male
  • United Kingdom
Share
  • Blog Posts
  • Discussions (9)
  • Groups
  • Photos
  • Photo Albums
  • Videos

Dan Houldsworth's Friends

  • James Overington
 

Dan Houldsworth's Page

Latest Activity

Dan Houldsworth replied to xoltri's discussion Pixhawk causing motor sync issues.
"Hi Kyle I'm no expert but I have used much of the same kit you list, so FWIW here are my thoughts : 1) Did you re-flash your AfroESCs? (See my overly length post earlier about that being the root cause of my similar issue with a 3DR Y6 +…"
Sep 5, 2014
Dan Houldsworth replied to Masu's discussion Pixhawk Data Logs on SD-Card
"But what if you only use APM Planner? Surely there must be a way to read these log files direct from card (I haven't found it yet....!)"
Jul 5, 2014
Dan Houldsworth replied to xoltri's discussion Pixhawk causing motor sync issues.
"To reassure myself that I hadn't somehow calibrated the throttle of the Afros without realising it, there are other reports of late 2013 shipments hitting max throttle at <1500us PWM here. It really does seem that a batch of Afro30amps…"
Jul 3, 2014
Dan Houldsworth left a comment for Dan Houldsworth
"Hi James I've just posted the scope readings. Amazingly, it disproves the hypothesis and in fact PixHawk has a clean PWM wave at 3.0v connected to either ESC while drawing up to 25amps. The only other possibility whereby this could still be an…"
Jul 1, 2014
Dan Houldsworth replied to xoltri's discussion Pixhawk causing motor sync issues.
"Christian - I take it back, it looks like your point 3 would have helped to isolate my problem after all......  :-)"
Jul 1, 2014
Dan Houldsworth replied to xoltri's discussion Pixhawk causing motor sync issues.
"Well here's some interesting results. I set out to prove the hypothesis that the PixHawk PWM voltage was sagging dangerously low under load due to the PixHawk having underpowered PWM drivers. I ended up showing that the PixHawk actually has a…"
Jul 1, 2014
Dan Houldsworth replied to xoltri's discussion Pixhawk causing motor sync issues.
"Hi Ritche - do you recall what props you were using on each set up? Also, which version of SimonK did you flash? "
Jul 1, 2014
Dan Houldsworth replied to xoltri's discussion Pixhawk causing motor sync issues.
"I've done a bit more digging on the Afro / SimonK params: O_POWER & O_GROUND are ohms to power, ohms to ground. Which I believe is a voltage resister divider to get a reference voltage at the PWM sense pin. It's always used as a…"
Jul 1, 2014
Dan Houldsworth replied to xoltri's discussion Pixhawk causing motor sync issues.
"Hi Christian Thanks for your reply. To be clear, I'm interested in feedback and information on the topic of the combination of Pixhawk + AfroESC giving unexpected behaviour, unexpected PID settings for normal flight, and / or motor…"
Jun 30, 2014
Dan Houldsworth left a comment for Dan Houldsworth
"Hi James Thanks for your comment. Having just read the thread links you sent, and in particular some of your comments and reasoning it certainly looks like you've identified the issue.  I do have a scope - albeit a cheap one…"
Jun 30, 2014
James Overington left a comment for Dan Houldsworth
"Re your post: http://diydrones.com/xn/detail/705844:Comment:1707558 Is there any chance you have access to a scope and can report back what the max signal voltage to both ESCs is while attached to the Pixhawk? (both the ESC that flys OK and the…"
Jun 29, 2014
Dan Houldsworth replied to xoltri's discussion Pixhawk causing motor sync issues.
"I'd like to add my experiences to the list, and am very keen to see this resolved for all. Frame : 3DR 2014 Y6 FC : PixHawk 3.1.4 Motors : 880kv (http://www.unmannedtechshop.co.uk/brushless-motor-2217q-880kv.html) Props : 11x6 HQ ESC : First…"
Jun 29, 2014

Profile Information

Please tell us a bit about your UAV interest
2x PixHawk, 1xAPM2.5, 4xOpenPilot Revo, 1xMegaPirate, 2xAfroAcro32
Hometown:
London

Comment Wall (3 comments)

At 12:00pm on June 29, 2014, James Overington said…

Re your post: http://diydrones.com/xn/detail/705844:Comment:1707558

Is there any chance you have access to a scope and can report back what the max signal voltage to both ESCs is while attached to the Pixhawk? (both the ESC that flys OK and the one giving problems) If you do not have a scope then a normal voltage reading from a DVM along with either the 'duty' (which is a common setting on a lot of meters) and/or the channel reading from MP for that ESC.

There has been some discussion over on the Drones-Discuss group

https://groups.google.com/forum/#!forum/drones-discuss

in this discussion

https://groups.google.com/forum/#!topic/drones-discuss/954zi9bAo84

from here specifically:

https://groups.google.com/d/msg/drones-discuss/954zi9bAo84/8pWf6iDKKr4J

I am by no means sure that there is a problem so I do not want to make a big deal about it on the main forum but I think it definitely requires further investigation and what you are describing seems to fit the profile. Hopefully the guys at 3DR are looking into it but going by sme of their comments, I do not necessarily trust that there will be full disclosure...

At 2:10am on June 30, 2014, Dan Houldsworth said…

Hi James

Thanks for your comment. Having just read the thread links you sent, and in particular some of your comments and reasoning it certainly looks like you've identified the issue. 

I do have a scope - albeit a cheap one (http://www.amazon.co.uk/SainSmart-Portable-Oscilloscope-Channels-Bandwidth/dp/B006BRCXL0/ref=sr_1_3?ie=UTF8&qid=1404118506&sr=8-3&keywords=oscilloscope) which I will need to figure out how to get some readings and will endeavour to get them over to you.

For my own learning (I'm not an engineer) can I just check I understand the issue :

  • Pixhawk uses the ARM 3v3 Digital Out pins, together with a 220ohm pull down resister to drive the PWM
  • APM uses a dedicated Atmel chip, again with a 220ohm pull down resister to drive the PWM but at 5v
  • On the surface of it the Pixhawk 3v3 approach brings it in line with the 'industry standard' of the big-name Rx which output 3v3 PWM, however it may be that the PixHawk experiences more PWM voltage sag under load from the servo / ESC signal connection.
  • There is no standard for logic level comparison - and likely ESCs are interpreting mid level voltages ~2v differently?
  • Using ESC/Battery negative as the signal return is technically feasible, but during high current loads the ESC -ve is likely to at a higher potential difference vs FC -ve, albeit small, and therefore reduce the reading of the PWM signal voltage.
  • Subject to further testing, it would seem that *most* ESCs out there draw sufficiently low current on the signal line and interpret ~2-3v correctly as high, AND probably average out signal noise to not have an issue with synchronisation with Pixhawk. However, if i) when the signal ground is not used, or ii) if a signal ground is used but the ESC draws too much load and drops the signal voltage - it would seem that too much noise is introduced into the signal measurement at the ESC with resulting synchronisation errors being magnified by those ESC that do not average.

I'm working from home tomorrow which should give me a bit of time to play around with the scope....

Cheers,

Dan.

At 7:47am on July 1, 2014, Dan Houldsworth said…

Hi James

I've just posted the scope readings. Amazingly, it disproves the hypothesis and in fact PixHawk has a clean PWM wave at 3.0v connected to either ESC while drawing up to 25amps.

The only other possibility whereby this could still be an issue is if the PWM voltage sagging only presents itself when multiple ESCs are connected (ie 6 on my Y6) but that would be difficult for me to bench test, and probably unlikely as there was no sag noticeable at all between the Afro and Quattro.

As you'll see from my post, I now need to build a reliable SimonK firmware and flash everything, and maybe from there I can be of help if this issue has still not been concluded.

Cheers,

Dan.

You need to be a member of DIY Drones to add comments!

Join DIY Drones

 
 
 

© 2019   Created by Chris Anderson.   Powered by

Badges  |  Report an Issue  |  Terms of Service