Locomotive Elevator

Hi Everyone, I'm back, oh no I hear you cry! I have been putting some bits together on the dreaded elevator, I have got one end set up and I loaded it with a 5kg steel block and the stepper motor will not lift it? I believe 4KG is about the limit of what the motor is capable of. When I run it the motor just grates as it keeps missing steps. Has anyone any idea how I can increase the torque on this so it will lift more please?

Cheers Phil

@thephilnewman 

A counterweight?

Does it work without 5kg steel block?

If it works without the 5Kg steel block just keep adding 1kg blocks to gauge the extent of the problem?

Do you have a video of it in action (or inaction)?  I was always curious to see what it looked like when finished. Even just a still image of the setup?

@robotbuilder I have tried with the weight it does not have enough torque the motor just keeps slipping when it is loaded with just over 4KG. It seems like it is struggling with the 4KG as well and the 4988 units are getting red hot even with the heatsinks on. I have them set to maximum current with the pots on them as well. I have the motor mounted with the shaft coming out of the bottom through a coupling onto a lead screw into a Plummer block on the floor, all mounted upright and vertically. So the motor is mounted upside down with the shaft coming out from the bottom of the motor.

Cheers Phil

@thephilnewman All elevators I know of have a counterweight. In fact, they are more likely to fall UP than down. HOWEVER, this only works if the 'car' weight is significantly more than the passenger weight.

I don't recall if you are using a transmission to reduce high speed and increase torque and if you went with cables or threaded rods. With cables, you would use blocks to increase torque. Since a quick search of youtube finds a few of these, it can be done, so maybe look at what they all have in common that may be different from yours.

I do recall a number of folks using a TV lift. That is certainly more than 5 kg, more like 25 kg up to 50 Kg. It was lifted with a single small motor.

@thephilnewman 

I just thought someone who has used these motors might recognize the symptoms if they saw (heard the noises) watching it in action themselves.

You wrote in the first post that the stepper motor limit was 4kg so why are you surprised with anything over that? What is the weight of the shelves? I thought you were going to use two stepper motors?

Others have used two stepper motors so if your setup is the same physically it should work.

Using extra reduction gears between the motor and the threaded rod or smaller threading on the rod will increase the lifting power but at the cost of speed.

Posted by: @thephilnewman

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Hi Everyone, I'm back, oh no I hear you cry! I have been putting some bits together on the dreaded elevator, I have got one end set up and I loaded it with a 5kg steel block and the stepper motor will not lift it? I believe 4KG is about the limit of what the motor is capable of. When I run it the motor just grates as it keeps missing steps. Has anyone any idea how I can increase the torque on this so it will lift more please?

Cheers Phil

You need to explain a bit more on your test setup and in the past you've variously mentioned nema17 and nema23 motors if I remember correctly.  Also, are we to assume your test of whatever motor you are using is driving a leadscrew and to that leadscrew you have attached a threaded a nut that is attached to a platform upon which you have placed weights?  If so, then apart from the leadscrew,  how is the platform otherwise supported.  How tight is the nut?   I just did a quick google on nema23 with leadscrews and I see that one quotes a thrust of 27Kg for a 'normal nut' though less with a non-backlash nut.

More detail required, and perhaps one of your entreating videos as well 😀 

@thephilnewman Wait a minute, only one motor on just one end? Then the load you test with should be half the total. Even better is 1/4 because 4 motors (one per corner) seems to be the simplest solution otherwise you need gears and such for 2 motors to enable lifting 4 corners.

@thephilnewman This is what I see a lot of. https://woodtechnology.com/product/whisper-ride-1000/

@thephilnewman 

There are quite a few things you can do.  Some have already been mentioned.

1. It would be helpful if you tell us how much current the circuit is actually pulling.  Although, I always adjust A4988 drivers, I've never really needed their peak output.  I do not understand the discrepancy between the product specifications saying Vref should put out 1amp, but the current draw doesn't seem to live up to that.
2. The easiest is friction.  Have you oiled the lead screw?  As the lead screw is responsible for most of the force multiplication any taken out in friction is greatly reducing the force output.  It really depends on how much friction it has to overcome.  If it freely spins like a flicking a nut on a bolt, that's as good as it gets.  If it feels like a nylon nut on a bolt, then that is most of your problem.
3. What voltage are you using?  As torque it ~proportional to wattage, torque is ~proportional to volts multiplied by watts.  I would assume the peak specifications of the A4988 are based on it running at its peak voltage of 35V.  24V will be better than 12V.
4. Next requires a driver change.  I've only used the A4988 which says it will only do 1A per coil.  The DRV8825 is a plug-in compatible driver.  All the pins are identical, the software doesn't have to change.  The prices are only a little higher than the A4988.  The DRV8825 says it will do 2.2A per coil which should get you nearer to the max ratings of your NEMA-23 steppers.  https://www.pololu.com/product/2133
5. Next the threaded rod that I originally suggested would also transmit more force as it has finer threads.  Depending on what you have locally.  Our equivalent here is 5/16"-18.  It would give you almost 3X more force than your lead screws.  It would require some software changes to compensate for the slower rate of movement.
6. As @zander mentioned, all elevators use counter weights.  It's the more complex mechanical options but will also work. 

@inq I didn't know if it was cables or threaded rods. Since it's a threaded rod, I assume there is a pulley and belt from the end of the rod to the motor, as it is highly unlikely the motor is designed to take very much, if any, weight along the longitudinal axis.

Another consideration is the difference between NC and NF threaded rods. NF might seem like a better choice as it might look like more threads per inch, but the NF thread profile is different with more area in frictional contact. As @Inq said, 5/16 18, and I would add 1/4-20, both being NC.

I wonder though if something like 3/8-16 PLUS a 2 to 1 driver and driven gear with a clogged belt would not be a better solution resulting in an effective 32 TPI system. Of course, even more extreme ratios can be used for even more torque. My uneducated guess is the motor is happier running faster with less load than slowly with a lot of load. Or maybe not, just a SWAG from an old curmudgeon.

Posted by: @zander

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Since it's a threaded rod, I assume there is a pulley and belt from the end of the rod to the motor, as it is highly unlikely the motor is designed to take very much, if any, weight along the longitudinal axis.

I'm not exactly sure what you're getting at with the pulley and belt.  But Phil had this picture early on.  I don't know what his current plan is.

I recommended he use pillow block to take the axial load and use the collets so that the motor took none.  I would have preferred the motor at the bottom and pillow block at the top, but horse for courses.

He has some pretty stout motors... 178 oz-inch.  If we can get enough current to them, he will not have any problem lifting the weights he's specified with just two motors.

Posted by: @zander

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I wonder though if something like 3/8-16 PLUS a 2 to 1 driver and driven gear with a clogged belt would not be a better solution resulting in an effective 32 TPI system. Of course, even more extreme ratios can be used for even more torque. My uneducated guess is the motor is happier running faster with less load than slowly with a lot of load. Or maybe not, just a SWAG from an old curmudgeon.

Well your old, so probably a curmudgeon 😀, its a badge of age and in a few years time I shall feel entitled to join the grumpy old men (but not quite there yet).  I expect the motor and leadscrew to be something like shown in the link below and should be good enough to lift a few Kilo's 

https://www.novantaims.com/hybrid-stepper-motor/lm23-nema-23-3-0a-1-8-external-linear-stepper-motor/#:~:text=NEMA%2023%20(57%20mm)%203.0,maximum%20life%20and%20quiet%20operation.

@byron Maybe I am misunderstanding, but the motor you linked is about 3 times the current. Not sure how that translates, but his setup doesn't work. The funny thing is that a single AC motor driving a TV lift can lift 100 lbs. The motor is about the size of a Coke can. The entire lift goes for $775 USD

Posted by: @inq

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Posted by: @zander

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Since it's a threaded rod, I assume there is a pulley and belt from the end of the rod to the motor, as it is highly unlikely the motor is designed to take very much, if any, weight along the longitudinal axis.

I'm not exactly sure what you're getting at with the pulley and belt.  But Phil had this picture early on.  I don't know what his current plan is.

I think the point was that if the lead screw is connected directly to the motor and the 5Kg weight is being applied directly to the motor's shaft then the motor will fail. Steppers aren't designed to support heavy loading along the shaft.

The lead screw should be installed with a thrust bearing to support the axial load and a gear or belt system to link to the stepper motor. That way there's no axial load on the stepper and it won't grind internally.

Posted by: @will

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I think the point was that if the lead screw is connected directly to the motor and the 5Kg weight is being applied directly to the motor's shaft then the motor will fail. Steppers aren't designed to support heavy loading along the shaft.

The lead screw should be installed with a thrust bearing to support the axial load and a gear or belt system to link to the stepper motor. That way there's no axial load on the stepper and it won't grind internally.

My take is that in the picture shown, the lead-screw is supported by the floor, and the motor does not have a 'pulling' load on it, and it just needs to rotate the lead-screw.  

But the platform that has an embedded nut for the lead-screw would need to be fully supported on each corner with steel rods that have linear bearings that can keep the platform on the level with a high degree of accuracy to prevent any twisting forces on the lead-screw nut.  It would seem that it would be best for the platform to either have the lead-screw in the centre, one at each end, or maybe to have one in each corner (and four motors of course) and do away with the rods supporting the four corners. 

But I make no claims to any knowledge of engineering, and it probably shows 😀