AX12 algorithm for moving

[Marmakoide]

Hi
For a personal project, I have to know how the AX12 computes the torque to go from pos A to pos B with the speed V. Is somebody knowing that ?

[Dewey]

Look at page 16 of the AX12 Manual.

The Ax12 moves to its goal position, addresses 30/31, at the speed V, addresses 32/33, if and only if the maximum torque in addresses 34/35 is not exceeded. If it is exceeded it will not continue moving and the goal position will never be reached no matter what speed is specified.

If the torque is not exceeded as it approaches the goal it reduced the maximum torque based on the compliance addresses 26/27 and 28/29.

So in the sense you ask the question it does not compute the torque merely limits it to the specified figure whenever a positional move is required.

Dewey

[Lenny]

I have monitored the load of three AX12's of my bioloid-arm randomly moving around.

x-axes is the load of servo 1
y-axes blue stars is the load of servo 2
y-axes red o's is the load of servo 3



Have someone an idea why the load is not uniform distributed?

Lenny

[JonHylands]

Its not really the load, and it only updates at 7 Hz.

What that value really represents is the amount of current the motor is consuming. If the servo isn't moving, then it gives a decent (although slow) approximation of load. If the servo is moving, you have to factor in the amount of torque you're inducing by the movement.

- Jon

[Fritzoid]

Marmakoide asked:

I have to know how the AX12 computes the torque to go from pos A to pos B with the speed V. Is somebody knowing that ?

I'd say it probably works something like this:

http://robosavvy.com/Builders/Fritzoid/AX-12.zip

[Fraser]

Hi Fritzoid,

The code is nice and readable, thanks for posting.

Slightly off topic, but then the thread is very old:

How did you generate the Temperature conversion table. i.e. what did you measure? the temperature of the servo case? the motor? temp sensor package?

(And do you mind if I use the table )

P.S.
I just noticed this, and thought I'd mention just in case operation is not as intended:

Code: Select all

// update temperature and voltage entries
if((++Timer0Count & 0x0100) == 0)
{
    ...
}


Block ... executes when bit 9 of Timer0Count is low, so executes continuously for 255 passes and then off for 255 passes. Should it be this:

Code: Select all

// update temperature and voltage entries
if((++Timer0Count & 0x00FF) == 0)
{
    ...
}


which executes once every 255 passes.

[Fritzoid]

Thanks Fraser,

In fact the line should read

Code: Select all

   if((Timer0Count++ & 0x01FF) == 0)


...which runs once every 512 passes.

What you are looking at is my best "reading" of the actual ax-12 firmware translated into c-like form. The output is meant to be used as a document that finally answers all the questions about the ax-12 algorithm for moving.

The input comes from an ax-12 storage dump posted in binary format on an earlier thread at this site, titled "Ax-12 firmware update gone wrong". You can find that thread from the Bioloid wiki page, reachable from the RoboSavvy site menu.

Because much of the translation process is done by hand and because it has never been compiled, there are probably more errors, like the one you identified, still in there. I'll fix them if someone points them out to me. Also, because the input is nearly two years old, the current firmware may have changed a bit.

The reason that I choose to post on this thread is because it is also linked to the Bioloid wiki page, an excellent resource.

[Fraser]

Wow, some nice work to decompile the Robotis ASM and add meaningful variable names to everything. I will check that thread out.

If I decide to try and implement a superset of Robotis firmware then your work will be a very nice reference. So many thanks for sharing it!

If I spot anymore errors along the way then i shall list them and send you a PM.

[Fritzoid]

I found a number of similar errors with bit mask usage.

The revised code has been placed in my files area.