[Josh Siegel]

Would you reccomend using a continuous cable system instead? The switch wouldn't be too hard, especially since we haven't started building, but I've heard those like to bind at the most inopprotune times, and you can't fix it on the fly like you can with cascading (reverse/forward again). Currently, we have 3 segments each weighing about 3lbs and some hardware to mount them, and a 4th piece on a slider with a pneumatic cylinder. 900lb cable (3/32" steel cable) should be fine for the load, but maybe the motors will be running too close to stall at that point. I did some math, but its probably off by (quite) a bit.

Formulas from a powerpoint I downloaded in the whitepapers section:
Fobject = 13lb
Dobject = 30"
Mslider = 13lb*30" = 390lb"
Fslider1 = 390lb"/(2*12") = 16.25lb
Fhit = .5*390lb" = 195lb"
Mhitlower = 195lb"*50"+(390lb"*(50"/2")) = 19500 something?
Flower1 = 390lb" + 19500/(2*20") = 877.5
Mhit = 195lb" * 130" + ((15lb*.5*130"))/2 = 812.5 something
Mbase = 390lb" + 812.5 something = 1202.5

Does that look reasonable for numbers? What about doability? I'm really liking the way cascading works, if its at all possible for us to do. A redesign at this point would set us back quite a bit, if continuous wouldn't work either.



edit: More usable math for potential gearing.


Telescoping drum – 2.5” diameter drum:
1. Speed - 2.5” radius drum, pi2.5”^2 = 19.5” circumference, 19.5” per rotation. Must move 60” of cables in order to fully extend. 60”/19.5” = 3.1 turns. Desired time should be about 5 seconds to telescope, so output must be ~37.2 RPM. Can be as low as 25 rpm.
2. Force – Will be lifting approx. 27lbs straight up, and headroom is needed. Gear for 35lbs.
Lever arm is theoretically the radius of the drum (2.5”). Force is 35lbs, to include some friction or potential weight discrepancies when the pneumatic cylinder is pressurized. 2.5” = .208’ * 35lb = 7.2 ft-lb.
Torque of the taigene motor @ 60RPM (12V) is 5.7 newton meters. 5.7 * .737562 = 4.2 foot lbs. Gear the motor down 2 to 1, you have 30 RPM and 8.4ft-lbs of torque, while still telescoping fairly quickly. Could gear down to 2.5 to 1 for 24RPM and 10.5 ft-lbs, assuming no loss to friction. Telescoping would take about 9 seconds at this point, likely too slow for autonomous, but the motors will not heat up like the FP motors after repeated use.

Telescoping drum – 3” diameter drum:
3. Speed - 3” radius drum, pi3”^2 = 28.2” circumference. 60”/28.2” = 2.1 turns. 5 seconds to telescope, so output ~25.2 RPM ((2.1/5)*60). 16 rpm for 8 seconds to telescope.
4. Force –35lbs.
Lever arm is 3”. Force is 35lbs. 3” = .25’ * 35lb = 8.75 ft-lb.
Stock torque is 4.2 foot lbs @ 60 rpm. Gear the motor down 2.5 to 1, you have 24 RPM and 10.5ft-lbs of torque, while still telescoping in 5 seconds. Could gear down to 3 to 1 for 20RPM and 12.6 ft-lbs, assuming no loss to friction.

Does this make sense? This basically tells me that the gearing on the motor should be based on torque and the diameter of the drum should be based on speed. The 3” drum looks a little more powerful at speed, but doesn’t it also take more power to move? I’m really starting to get lost in the math :S