AX12 control oddities

2009-05-20T05:21:19+01:00

Hi, ok, so the following pseudo-code is performing the intended goal, meaning that a very naive approach works well enough

Code:: lSamplingFreq = 0.05 lUpdateDuration = 1 / lSamplingFreq // Rough initial estimate lPos = 0.0 lGoalPos = 0.0 lSpeed = 0.0 lStartTime = lUpdateStartDate = lUpdateEndDate = getCurrentTime() while(1) { // Compute the next pos lT = lUpdateStartDate - lStartTime + lUpdateDuration lGoalPos = 0.5 * Constantsf::PI * sin(lT) // Read the current pos lPos = lServo.readPos() // Compute the speed lSpeed = abs(lPos - lGoalPos) / lUpdateDuration // Send the command lServo.moveTo(lGoalPos, lSpeed) sleep(1 / lSamplingFreq) // Compute update duration lUpdateEndDate = getCurrentTime(); lUpdateDuration = lUpdateEndDate - lUpdateStartDate; swap(lUpdateEndDate, lUpdateStartDate); }

sleep => do nothing
Time => seconds
Angles => in radians
Speeds => in radians per second

The precision obtained is really nice, and what is nice is that code is sampling frequency independent.

Statistics: Posted by Marmakoide — Wed May 20, 2009 5:21 am

AX12 control oddities

2009-05-19T12:16:33+01:00

Hi,

=== The intented goal ===
I'm trying to understand how to have an accurate control of a AX-12 from a PC with an USB2Dynamixel interface.

I want it to move as following
x(t)=0.5 * pi * sin(t)
where x(t) is the angle in radians and t is the time in seconds

=== My approach ===
I use a very naive approach. I repeat in an infinite loop the following instructions
1) Compute XGoal = x(T+K)
2) Read the current position XCurrent of the AX12
3) Compute V=|Xcurrent - XGoal| / K
4) Write the AX12 register to move to XGoal at speed V
5) K = time elapsed to do step 1) to 4)

When watching XGoal and XCurrent, XCurrent is always a bit late, being behind XGoal. A perfect control would achieve XGoal = XCurrent, up to a given error of course

=== My question ===
How do you, ladies and gentlemen, would do that very simple task ? A less naive approach ? My approach is just broken ?

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Statistics: Posted by Marmakoide — Tue May 19, 2009 12:16 pm

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AX12 control oddities

AX12 control oddities