What kind of motor should I use for lifting a heavy load?

[lopezj50]

I'm working on an automation application in which I need to control a lifting mechanism with heavy load (about 120 lbs).  I will be getting constant temperature readings and based on that data I can determine the rate of change of the temperature.  If the temperature rate is too fast then I need to be able to slow down the motor, if it is too slow then I need to speed it up.  I'm looking for some support with choosing the right motor and hardware so that I have full speed control, while still being able to lift this heavy load, hold the load in a certain position, and then raise the load back to its original position.  I was considering a stepper motor for this due to its ability to brake so the load can stabilize.  Is this the right call or should I use a continuous servo?  Where can I get such a stepper that can handle this type of load and has software that interfaces with LabVIEW?  Would I be safe getting low-cost hardware for this application?  Any guidance would be sincerely appreciated.  Thanks.

[Brian_Beal]

A stepper sounds like it would work, and is less expensive than a servo system.  What you really need to determine is the mechanism you will be using between the motor and your load.  A gearbox?  A linear actuator?  Please give us some more information.

[Buechsenschuetz]

I think the best choice for the mechanical interface would be a worm gear. In most cases these are self-latching when a load is applied and the drive is shut off, similar to a screw which cannot be pushed straight into the thread.

[Brian_Beal]

That is true about the worm gear.  The bad part is that it is not effecient, and you will need a bigger motor to lift the same load.  If you give me the load, speed, and mechanism details, I can tell you the motor requirements.

[lopezj50]

Thanks for your replies to this topic.  I just discovered the worm gear option yesterday while talking to a professor.  I think that is the route we are going to take because the DC motor won't be as expensive as a high-torque stepper or servo.  Also, I have three engineers that will be calculating the motor size based on gear reduction, spool size, cable length, and the load that we have to lift (which is about 120 lbs.).  If any of you would like to suggest a motor size, that would be great too.  I'm thinking something around 1HP should probably do it.  My goal is to stay cost-effective while making an easy apparatus.  I know that the worm gears may also be inefficient at times but it seems like the best solution for this application.  Not to mention it's not to hard for our mechanical engineers here to make the spool and bearings.  And I believe you can buy a DC motor that interfaces directly with a worm gear.  However, a follow up question is what computer hardware do I need to control the voltage of the motor so I have speed control?  Is this done through an RS232 board?  My output from the LabVIEW program will be voltages, from which device is that binary signal converted into physical voltage?  Thanks for your help so far.

[J.Harv]

Lopezj50-

       Between the motor and the software (LabVIEW) you will need a motion control card and possibly a motor amplifier or drive.  I would recommend going to www.ni.com/motion  this webpage has links to our various motion controllers and comparisons on them.  Also, in the top left there is a link titled "Learn Motion Control Basics" I would read through that to get a better idea of what you need. After you have looked through this I would give us a call at (888) 280-7645. This will get you on with a saled rep. who will know our products and based on what you need can recommend the remaining pieces for you system.  If you have any questions give us a call.  Thanks

John H
Applications Engineer
National Instruments
http://www.ni.com/support

[lopezj50]

Thanks John, I appreciate the help.  I navigated through the Learning Motion Control basics and realized the pieces that I may need to control the speed of the motor.  It seems like I need the motion controller that will interface to an amplifier, if needed, and then the amplifier will take the leads to the DC motor.  I guess what I'm asking are what motion controllers would I use specifically for controlling DC motors, or does it not matter?  I would like to be pointed to the actual part # if you could.  If not then I will call the Sales Rep either tonight or tomorrow.  Thanks.

[Brian_Beal]

If you are using an open loop,  brushed DC motor, then I would just get a DC drive that accepts an analog input for speed control.  Minarik is one name that comes to mind.  Some of the drives are available with limit switch inputs, which I would recommend.  You may also find one that has a comms option, but that is more rare.  With the analog input option, you would need to get a DAQ device that has analog output.  A USB-6008 will probably work for this application.  You will want to size the motor before you pick out a drive.

[lopezj50]

We should have the gear ratios as well as the motor size needed to lift the load by tomorrow.  Once I get that I can call NI and give them the specs.  I need to get this thing ordered because I know we'll have some lead time for receiving the stuff.  I'm just scared since this is the first automation system I'm working on and the budget is limited.  I just want to make sure that I can communicate with my motor, via some device, so that I can control its speed.  Ordering the motor, the worm gear, and making the spool for the cable and everything shouldn't really present a problem.  The logistics behind making this thing work are a little tougher.  We should have it worked out by the end of this week.  If this helps any, I already ordered a USB-6210 to read the voltages coming in from my sensors.  Would I be able to use one of the digital outputs on this device to control motor speed?  With modulation perhaps?  I'll check up on the specs sheet and try to make sense of it.

[Brian_Beal]

I would see if you can get the 6210 changed to a 6211.  You might find a motor controller that uses digital inputs for preset speeds, but it sounds like you really need an analog signal.