Has anyone done or heard about any working measurements on cylinder pressures to help
calculate actual digging forces?
It is an interesting question. The calculations are quite easy and I have made them many
times.
For years, I have tried to do a fair comparison of backhoe attachments for compact
tractors. The problem is that the manufacturers typically put digging forces into
their spec sheets, but don't always tell you what the hydraulic pressures are. Consequently,
it is hard to do a fair comparison between hoes.
What I did is measure the dipper cylinder OD, the dipper stick length, and the dipper stick
arm in the field. I then calculated the cylinder force as well at the "dipper stick ratio". The
DSR is the ratio of the DS arm to the DS length. The DS arm is the distance between where
the DS cylinder attaches to the DS, and the DS pivot point. I then calculated the digging
force at the bucket pivot in the maximum case. The max is where the DS arm is perpendicular
to the boom.
Well, Excel is a wonderful tool, and I made a spreadsheet with the formulae entered. Here
is a snapshot for some of the hoes I have measured. Note that I am able to compare them
using 2 different hydraulic pressures 2000 and 2500psi. I had to estimate the cylinder IDs if
I did not have that info. Cyls of this type usually have about 0.2" wall thickness.
Also note that I have ignored the "breakout force" calculation. The BF depends on the
bucket geometry (length of bkt pivot to end of tooth).