Thank you, I'll look into the continuous cable systems. From what I understand, they offer lower tension at the cost of having to move more length of cable, which means a faster motor with the same ability to exert a force.
I'd really like to use continuous, but I'm worried about the speed. Assuming the force needed (not tension) to move the object is the same, cascading is much faster which will become critical in autonomous mode. This would allow us to gear a motor down for more power and have it lift the tetra in the same amount of time.
edit:
Here's what I've got on the new calculations for continuous, I just need to find out how to relate the power of the motor and the power needed to lift the arm.
Power = 12.6ft * 35lb/5 seconds
Power = 88.2ft-lb/sec = ~.18hp or 132.3 watts
Taigene motor specs (ungeared) – 5.7Nm @ 63RPM @ 12V. 5.7Nm * 0.738 = 4.2 ft lbs. 67 watts
3” diameter drum = 28.2” circumference. 152”/28.2 = 5.4 rotations.
5.4 rotations in 5 seconds, so 65RPM.
So is it...
88.2ft-lb/s/63 rotations = 1.4ft-lb/rotation = 33% of stall output, appropriate for direct drive?
or
4.2ft-lb/1.08RPS = 3.89ft-lb/s where the motor is underpowered?
I also ran the numbers through JVN's gear calculator with a 1:1 ratio and 3" torque arm radius. Stall load is 81.42lbs. With an applied load of 30lb (tension of the cable), it says the motor load torque is 10.2Nm. Seems like this motor is underpowered...
Maybe cascading 3 to 1 is the way to go, if this design must be used. The CIMs are all taken up, the FP needs to be running to cool itself (so it can't hold the arm) and the globe motor is too slow according to 61 who used it to telescope a continuous arm in 2004.
Josh