HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Sep 27, 2011, 05:59 PM
That tree again!!!!
thanhTran's Avatar
Germantown, MD, US
Joined Sep 2004
6,642 Posts
Quote:
Originally Posted by photronix View Post
Well said.

Now back to the question. Any idea why Turnigy work well? They are essentially a low pass filter. It's a bottle neck that people seem to ignore and I can't figure out why.

Thanx for the info.
Maybe the Turnigy low pass filter has a correct cut off frequency that not too low or too high?


Thanh
thanhTran is offline Find More Posts by thanhTran
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 27, 2011, 06:04 PM
That tree again!!!!
thanhTran's Avatar
Germantown, MD, US
Joined Sep 2004
6,642 Posts
Quote:
Originally Posted by jes1111 View Post
I believe (and please don't jump all over me if I get this all twisted) that the answer to this conundrum lies not in whether the motor can meaningfully respond to signalling above 100Hz but in the rate at which the FC is calculating new commands. By blasting the ESC with commands at 400Hz (or 1000Hz, or whatever) you ensure that when the ESC/motor does react, it's acting on the very latest command, not one that was issued "eons" ago. In other words, rather than discarding all the intermediate calculations that the FC does in 20ms (which is effectively what you're doing at 50Hz update rate), send as many of them as you can to the ESC and let it "do its best" with up-to-date commands.
I think your point explains it. The controller doesn't know when the ESC is ready to accept new throttle value. The ESC is not always ready. It has its own loop that reads the pulse length, calculates the PWM value, and checking the rotor position, and turning on the power to the motor. Only a portion of this loop that the ESC is accepting the pulse from the flight controller.
thanhTran is offline Find More Posts by thanhTran
Reply With Quote
Old Sep 27, 2011, 06:11 PM
Tri-Quad-Hexa-Octo-copters!!
United States, TX, San Antonio
Joined Feb 2007
14,669 Posts
Hi El,
Well you are using Turnigy Plush ESCs with about 300Hz update rates and indeterminate PWM update rate from the gyros. That would have to be measured to be valid. Plus your arms are on the large side so lower updates rates are OK. We would have to measure them to be sure. It flys nicely, but not significantly better than the previous video that was in fact a smaller tricopter hovering indoors at a low altitude with lots of prop turbulence. Like all these videos, they need to be compared to similar build and similar flight conditions. As an example there are nice XUFO flight videos, but in reality those with the original mechanical gyro fly terribly compared to any of the multicopter setups out there that we enjoy flying today
Cheers,
Jim
Quadrocopter and Tricopter Mega Link Index
jesolins is offline Find More Posts by jesolins
Reply With Quote
Old Sep 27, 2011, 08:39 PM
Suspended Account
Joined Dec 2010
11,764 Posts
Quote:
Originally Posted by photronix View Post
Well let me ask this. Considering the transfer function curve there is no response past about 50hz. Since many of us are using turnigy do you believe changing pwm faster than 100hz has any effect on flight? Because according to the data it wouldn't be possible. I am really interested to know your thoughts.
The thing is, some (original) ESCs use the PWM *period* to base their throttle ramping etc on. So they will take let's say 10 periods to ramp setpoint from A (now) to B (set), at 50Hz that would be 20*10ms = 200ms, but at 400Hz that would be 2.5*10ms. (Ignoring for a minute any other factors). That is one of the reasons.
timecop is offline Find More Posts by timecop
Reply With Quote  (Disabled)
Old Sep 28, 2011, 01:36 AM
Registered User
andrebandre's Avatar
United States, NM, Clovis
Joined Jul 2006
615 Posts
Quote:
Originally Posted by jes1111 View Post
I believe (and please don't jump all over me if I get this all twisted) that the answer to this conundrum lies not in whether the motor can meaningfully respond to signalling above 100Hz but in the rate at which the FC is calculating new commands. By blasting the ESC with commands at 400Hz (or 1000Hz, or whatever) you ensure that when the ESC/motor does react, it's acting on the very latest command, not one that was issued "eons" ago. In other words, rather than discarding all the intermediate calculations that the FC does in 20ms (which is effectively what you're doing at 50Hz update rate), send as many of them as you can to the ESC and let it "do its best" with up-to-date commands.
It makes a lot of sense to me.
andrebandre is offline Find More Posts by andrebandre
Reply With Quote
Old Sep 28, 2011, 07:31 AM
Registered User
Joined Feb 2008
85 Posts
Do different motors have different response rates? Seems to me that a very large motor swinging a very small low pitch prop could respond much faster than a small motor swinging a large prop.
Justin Stuart is offline Find More Posts by Justin Stuart
Reply With Quote
Old Sep 28, 2011, 08:14 AM
checkout my Blog
otlski's Avatar
Joined Feb 2008
467 Posts
Justin,

The answer to your question is yes, conditionally. That condition mainly being that the larger motor has more net torque available. First off, I would describe it as a system response rather than a motor response. The combined response of the motor and prop is dictated both by the available torque and the system's resistance to angular acceleration. The resistance to angular acceleration has three main components; the prop's profile drag, the prop MOI, and the motor bell MOI. On the MOI side, the prop's MOI is significantly larger than the motor bell's; so the larger motor and small prop combined MOI is likely smaller than the smaller motor and larger prop MOI. Add in the smaller profile drag of the smaller prop and the assumed higher torque of the larger motor, and your statement holds up.

Dan


Quote:
Originally Posted by Justin Stuart View Post
Do different motors have different response rates? Seems to me that a very large motor swinging a very small low pitch prop could respond much faster than a small motor swinging a large prop.
otlski is offline Find More Posts by otlski
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question MotorFly ESC PWM Frequency Setting ZackJones Power Systems 0 Jul 24, 2011 11:47 AM
Question Hobbywing ESC PWM frequency? abenn Power Systems 4 Jul 03, 2011 05:13 PM
Discussion ESC timing and frequency Uno Electric Ducted Fan Jet Talk 13 Jun 08, 2011 03:31 PM
Discussion Sensor update frequency skogsvargen UAV - Unmanned Aerial Vehicles 2 Sep 15, 2006 02:00 PM
Frequency List Update Don Leitz VOA Flyers of West Chester Ohio 5 Mar 15, 2003 04:39 PM