Can anyone validate my motor calculations?

[LoneWo1f1998]

My team is debating using the andymark am-2971 planetary gear box with motor and encoder to lift up the stack of crates. We would have it attached to a three inch diameter sprocket with chain running to the bottom of our lift mechanism and the top in a triangle. I am relatively inexperienced in calculating torque and lift capacity so I tried to use a spreadsheet application, but would like to check my numbers since I wasn't sure on some of the values. We would have one or two of the motor-gearbox combinations, one for each side of the lifter so I assume they would each need to lift 30-40 pounds or one motor lifting 60 to 80 lbs. When I put in all of the numbers, the app told me the design could lift the whole stack 17 in in 2.32 seconds and would have a stall load of about 106 lbs. I wanted to make sure these numbers were right before we committed so if anyone who understands this stuff more could check them that would be great. I would also appreciate suggestions for a better system, but please keep in mind I am rather new.

I'm assuming that a 3" sprocket translates to a 1.5" Load Torque Lever arm. and input a 1:1 gear reduction because we put in the specs from AM on the gear motor itself.

Performance Specs:
Gearbox Reduction: 71:1
Total Counts per revolution: 497 (7 Counts per motor rotation multiplied by gearbox reduction, 71)
Voltage: 12 volt DC
No Load Free Speed: 75 rpm
No Load Current: 0.6 amps
Tested Gearbox Output Power: 44 Watts*
Stall Torque: 16.6 ft-lbf*
Stall Current: 22 amps*
Minimum torque needed to back drive a non-powered PG71: 1.3ft-lb
Maximum torque applied at shaft which breaks gearbox: 39 ft-lbs (breakage point is shearing of shaft)