Lead screw Actuated telescoping lift

I have a 1 inch travel per revolution lead screw powering my telescopic lift, which will be lifting a maximum of 35 lbs at any given time. Any suggestions as to which motors i should use and how i should gear it? I’m thinking a Mini CIM with a 20:1 reduction will be sufficient.

Looks like if you want to lift in say five seconds,about 20 inches, you’ll need to be lifting about 4 inches per second. If you lift one inch per revolution, you’ll need an output that is min 240 rpm. That takes all of the seat and window motors out of the running.

For a full CIM that’s free speed is 5400rpm, so to get to 240rpm you’ll want about 22:1 gearing. But if you’re turning four (presumably ) lead screws with chain and sprockets, you could get some additional reduction with the sprockets. Mini CIM is 5800 rpm, but for most purposes you can just figure they’re they same.

The 775 Pro turns 18K rpm, so you’d need a 75:1 gearbox. I’m not sure which to point you to for that much power at that speed.

Transmission-wise, you’ll need something rugged–most of the single speed drive transmissions (tough-box, cimplebox) are designed for higher gearing–I think about 14:1 is the deepest these go. Probably can’t use them unless you have a 2:1 ratio in the sprockets.

Planetary transmissions seem to be more where you’ll end up. I’m a fan of Banebot P80, because they never fail, but they cost much and 27:1 is as close as you get to that 22 ratio you need. But there are many options for planetary transmissions now. Some compact and light. Dynamo, Sport, Vexpro. I don’t have experience with any of them.

Without doing the math, I can tell you that a Mini Cim at 27:1 lifted our Steamworks robot in about four seconds, so I think the wattage is probably fine on a Mini CIM. But if you have room/weight for a full CIM, extra power isn’t bad.

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Ignoring friction for now, a mini-CIM reduced 20:1 will provide an output stall torque of 28.2 N-m, or 20.8 ft-lb. Applying that over 2pi radians will give one inch (1/12 ft) of travel, meaning that the stall force is 1568 lb. Working around the peak efficiency of the CIM will yield about 250 lb of force. At that point, the miniCIM will be rotating about 4800 rpm, the output of the gearbox about 240 rpm, and the load about 20 ft/m or 1/3 ft/s. Unless your “telescopic lift” is some sort of scissors which moves a lot farther at the load than where you’re applying the lead screw, sounds like you don’t need nearly that much gearing.

Here is a vex lift similar to how mine works. the end will be moving at 4 times the speed of the lead screw nut. So correct me if i’m wrong, but the end will have 62.5-ish lbs of force, and move at 1 1/3 feet per second. i was looking for something closer to 2 feet per second. So i’m guessing around 16:1 with a CIM motor. I’m not in a position where i can do the calculations right now, but i know vexpro versaplanetary, i can do an 8:1 gearbox, and a 2:1 gear ratio connecting the gearbox to the screw.

@hrench, Although that’s not what i was asking about, i actually do have a 4 post lead screw mechanism on my robot for climbing onto the 3rd platform. not sure how you guessed so accurately, but the information you gave is appreciated. I think that’s how I’ll do it.

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That’s what I was missing. Yes, then ~62# and 1.3 ft/s at max efficiency, no friction. To get 2ft/s at the end, I’d shoot for 12:1 or 10:1.