Motor with programmable controller 1

[WRUMMEL]

I have a project that I need help picking a motor/controller for. I have a jack that will lift a 300 pound load up and down. It requires about 8 ft. Lbs. of torque to rotate the hex bolt on the jack. I know it needs to rotate 20 revolutions to fully extend up. I'd like to add a motor that can be controlled to rotate the jack up. Then bring it back down. But as it comes back down it knows to automatically turn off. Also if it could automatically slow down as it approaches the lower end so it doesn't slam the load to the floor that would be a bonus. Any ideas? It sounds like I might need to program a controller that will operate it by the touch of a button to power the motor for 20 revolutions. Then when it comes back down to be programmed to vary the speed such that is gradually decreases as it reaches the bottom. I didn't know if there would be any off the shelf motors and controllers that might work for this. Thanks.
Also my power source is a 120 V AC.

 

[waross]

Is the 8 ft. lbs. the operating torque or the torque required to overcome sticktion.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[WRUMMEL]

That's to overcome friction. Operating is probably closer to 5-6

 

[waross]

You're ahead of me there. Stand by. One of the gurus with more experience with small motors and drives is sure to offer good advice.
By the way; How far does the jack travel and how fast do you want this to raise the load? The drive guys will want to know.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[BrianE22]

Are you o.k. with the load resting on the floor or do you need to support it in the air? If supporting it in the air you might want to use self-locking worm gears. For self-locking the gearbox efficiency would probably be below 60%

 

[WRUMMEL]

The jack raises just about 2-3 inches. But the important part is I just want a motor that can attach to the 7/16" hex but that drives the jack. The nut must rotate 20 times to achieve this range. I'd like to somehow program a cost effective motor that will run this at a low (I was thinking around (10-40) rpm. When it's in the middle of range, rpm can be higher. But at as the motor stops, I'd like it to slow to a stop, or at least run at a continuous slow speed.

Once the jack is lowered all the way, it rests the load on a support. So it doesn't matter if the jack lowers all the way. I just have to make sure it stops.

 

[3DDave]

You can get an electric car scissor jack pretty cheap; 12v and add switches. $62 at Home Depot for 2000 pound capacity. Cheaper at harbor fright if you like. No mounting, no adapting, and no finding the right motor. The thread is coarse enough you can put a limit switch where the end pokes out and another for the down position.

 

[WRUMMEL]

The problem is it has to be a very low profile jack. Less than 3 inches. I already have the jack. I'm just treating the system as the nut on the jack and the goal is to rotate it automatically, since it will be operated very frequently. It would save a tremendous about of time to not have to hand crank it.

 

[itsmoked]

I've hand made something to do this so let me share my experience about it.

I made an aquarium stand that would raise and lower a 3,000lb tank. I carefully measured the torque required to turn the jack crank and using a VFD controlled gear drive reduced further via chain/sprocket reduction to give the drive system 50% more torque 'than needed'. With 3000lbs on the stand it drew 240% of the motor's full load amperage (FLA) to shudderingly and hesitatingly creep the stand upward. I had to add a second sprocket set to further reduce the drive ratio so I had about 300% of the measured torque.

Lesson: Provide more than 200% of the expected torque requirement to account for binding/wear/etc.

Next, with even the first ratio above there was absolutely no need to bring anything to a "soft landing". The system coasted smoothly and quickly to a stop in either direction from full speed. I'd estimate on my project the load came to a stop in about 1/16".

Lesson: You're likely overthinking it on these take-off and landing issues.

Dumping the tapered motion you then need only an UP/DOWN button and the VFD setup for an UP (OR) DOWN input. You then include micro-switches on your system that disconnect the UP or DOWN signals when the heights are reached. That will stop the motor and you'll get a tiny coast to where you want the load to be.

If you actually prove you have to have the added cost and hassle of tapered stops you can use an intermediate method that will likely still work fine. You use two additional micro-switches near the ends that command a different (slower) speed of the VFD. VFDs all have the provision for a digital input that when active causes the VFD to use a fixed preset (by the user) speed. When these 'speed switches' are active the VFD will slow to whatever you set it to for the switches - likely one slow speed is more than adequate since in my experience none are needed. If one slow speed is acceptable for your system just put them both in parallel so you only need to set one alternate speed.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[3DDave]

Then maybe strip the motor and gearbox and wiring and put them on your jack. The one I suggested gets down to 5 inches.

Is this a lab jack?

I feel like this is working towards 20 questions.

What washdown requirements are there?
Is there a need for spark control?
Is there a reason a simple cam and a lever won't work?
Is there a reason not to counterweight/balance spring the load?
Is there a time requirement?
What is the static torque to overcome?
What is the running torque to overcome?
What mounting provision is there for mounting the motor?