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Originally Posted by asid61
If you use the jvn design calculator it makes all this calculation much easier. According to that, you are running 38 amps when you are lifting 70lbs- a lowish estimate for claw + totes + bin. However, when you factor in efficiency and random junk getting in the way, you should be gearing it down even further, maybe with a second 2:1 reduction to make your overall reduction 140:1.
That nets you a speed of 1.7ft/sec and has a big margin of safety.
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The free speed of the RS775-18 at 12 volts is 13000 rpm. With a 140:1 gear reduction and the 6" diameter winch drum and 2:1 pulley reduction in the OP's design, that's only 1.2 feet/sec load speed. And that's with the motor at free speed... so with a load you'll be nowhere near that speed.
Start with required power and work from there. Take the 70 pound load and add a 50% margin (or more!) to account for friction and other factors. That's 105 pounds.
The mechanical power required to lift a 105 pound load at 1.7 ft/sec is 105*1.7*1.356=242 watts. From the motor curve at 12 volts, the RS775-18 will generate 242 shaft watts at 8632 rpm while drawing 30 amps. At that operating point it will be generating 122 watts of heat, which is about 4 times the heat it generates at max efficiency (and at much lower speed). So this is far from optimal for that motor.
Now calculate the required speed reductions. To get 1.7 ft/sec with 8632 motor rpm, you'll need a gear ratio of about 66:1 (with 6" diameter winch drum and 2:1 pulley).
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You can use a 70:1 reduction if you run a cim, as that will only draw 21 amps at max load and give you a max loaded speed of 1.6ft/sec. I do not know how slow you would have to run if you choose to brake with the motor alone.
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The CIM's free speed is 5310 rpm. With a 70:1 gear reduction and the 6" diameter winch drum and 2:1 pulley reduction in the OP's design, that's only 1 foot/sec load speed. And that's with the motor at free speed... so with a load you'll be nowhere near that speed.
Again, start with required power and work from there. You need 242 watts (see above). From the motor curve at 12 volts, the CIM will generate 242 shaft watts at 4065 rpm while drawing 33 amps. At that operating point it will be generating 157 watts of heat, which is about twice the heat it generates at max efficiency.
Now calculate the required speed reductions. To get 1.7 ft/sec with 4065 motor rpm, you'll need a gear ratio of about 31:1 (with 6" diameter winch drum and 2:1 pulley).