Thread: Discussion ESC Response Testing
View Single Post
Old Dec 15, 2010, 12:42 PM
obor is offline
Find More Posts by obor
Registered User
France
Joined Nov 2003
287 Posts
Quote:
Originally Posted by pando14 View Post
Calculate time response after a stepup (stepdown) input give you the same info than response after rampup (rumpdown) because in digital mode a ramp is made by steps! So a fast time response after a stepup (stempdown) means a fast time response after a rampup (rumpdown)
I agree with you if the rampup(or rampdown) is reached before the next PWM duty. If not, then the way firmware handle rampup or down may interfere.

Quote:
Ok, I understood why you can't reduce time between measures, i had the same problem in another project! What i mean with
is that for example in your graph of 50msec between PWM change, with your measure frequency, you maybe can't correctly describe RPM behaviour.
Yes, you are right, with small PWM period changes like 50ms, the RPM capture every 25msec is not accurate enough.

Quote:
I divided you graph to show better the period and in my example (i zoom - sorry for very very bad quality - period 3) the blue line indicate the real RPM behaviour and red cross data captured with you measures(ok, this is a very unfortunate case but it's just to explain). So your measure show no RMP change but in reality there's change. In addition to this problem there's the RPM approximation caused by the low accuracy (1/6 turn). The sum of this two problem is clear in your graph because the RPM behaviour is different in every period (for example from 1 to 9) instead it should be the same because in every period you have the same input sequence.

At the end, with this measure frequency you couldn't appreciate, at "high" frequency (for example 50ms between pwm changes), the difference between two esc response.
I wanna say that I don't want to destroy your work, instead i want to help you to find a method to compare different esc response .. maybe we have to think about using current measure.
I agree with this, with small period like 50msec ,measurement are not accurate enough. But do we need to measure that low ? I did 100 msec measurement, but could try also 150 or 200 msec between PWM changes.

If we consider that it takes approx 4msec for a turn a full speed, then with 6 magnets it gives:
- in 4 msec, Magnet seen vary between 0 - 6
- in 8 msec, it gives 0-12
For RPM varying between 2000 and 3000, that means 0-3 to 0-4/5 in 4 msec, which 1 or 2 magnet more or less per turn, which is not enough.
I'll try to double the number of magnets.
obor is offline Find More Posts by obor
Reply With Quote