RoboSavvy Forum

AX-12 : Present load, Punch and Center of Mass

2008-12-03T08:21:13+01:00

Present load:

This output is surprisingly low resolution and surprisingly noisy. The units also don't appear to be anything really useful. Do bear in mind tha the friction of the drive train is very high so the servo can actually be holding a load with very little motor input. Conversely the motor needs a surprisingly high surge of current to overcome the same friction in the drive train. Which brings me to ...

Punch:

The 'punch' is effective a surge of current to the motor to start it moving. It's primarily used if the motor is idle (because the goal position is within the 'slop') and the goal then drifts too far away. The motor is then 'punched' with this surge of current to try to quickly correct the position without the servo drifting too far. It's this punch that causes the servo whistle.

Centre of mass:

I've never worked this out, never really considered it important to determine the difference between centre of volume and centre of mass, but it's easy enough to figure out.

If you hang the servo from a piece of string the centre of mass will settle under the centre of pivot. By selecting a few pivot points you could quickly determine where the centre of mass is.

I suspect the centre of mass is probably fairly central but biased towards the motor maybe about a third of the way along the casing. The motor is the opposite end to the servo horn and is the only heavy item in the casing.

Do publish any answers you find

Statistics: Posted by StuartL — Wed Dec 03, 2008 8:21 am

AX-12 : Present load, Punch and Center of Mass

2008-12-02T22:33:05+01:00

Same questions here... please share your findings.

I sure hope i'm wrong here, but after going trough a lot of manuals recently it seems the load can not be polled directly... An upper (register 0x28) and lower (0x29) load limit can be set however. These trigger the 5th bit (overload error) at register 0x11.
I've seen people do AX-12 load-feedback by setting torque a little lower, and using the current position register to measure obstacles or mass.

Don't have the equipment myself, can't validate anything. I assume (its MOAFU i know) 1..254 is 1..100% load, where 0 is disabling the feature.

Link: http://robosavvy.com/RoboSavvyPages/Sup ... nglish.pdf
~~Strange why that link wont work..~~

Statistics: Posted by Barryke — Tue Dec 02, 2008 10:33 pm

AX-12 : Present load, Punch and Center of Mass

2008-11-28T19:07:26+01:00

I was wondering if someone can explain me these two registers of the AX-12.

Do we have more information on the value returned by the present load, in which unit it is expressed. Do you think it is possible to calculate the torque apply by something on the servo with it and with which accuaracy ? Finally, maybe I could find answer to my question if someone know how the value returned is calculated or if someone has already realised a detailed study of the "present load". In all the cases, I accept all types of information .

For the Punch one, It's just because I'm affraid to not understand the description given by the manual...Can we reserve a certain quantity of current for the motor ?

My last question is about the caracteristics of the AX-12. The weigth is given : 55g but does anybody has already study the repartition of mass in the stuff in order to determine the center of gravity ?

Thanks for your interest and answers

Statistics: Posted by Ynothar — Fri Nov 28, 2008 7:07 pm