I can see that if your using 1"-3" robots Leica recommend their current GDF322/GDF321's but what are the older ones that are still suitable (i.e. meet the torsional rigidity or hysteresis requirements)?
GDF122/GDF121's ??
GDF22/GDF21 ??
I have no idea. If you are buying new I would buy what is recommended. If you are looking to use old ones that you already have have you should test them out. Set them up, work them out for awhile, then check your backsight. I'd expect that you will find much more drift with anything other than the recommended tribrachs.?ÿ ?ÿ?ÿ
When the "plastic" tribrachs came out we didn't like them and decided the old metal ones (GDF6) were more robust; we built up our stock from ones that others had traded back in the the new ones, so we now have 16.
They have been used with robotics since our first GDM4400 (March 1991). We have never had any problem with any drift. The grip on the instrument has always been complete. As with all equipment proper care and maintenance pays dividends.