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Mechanical Design Assistance???

RWReynolds

Hey everyone,

 

I'm not a mechanical engineer by any stretch on anyone's imagination. I have one mechanical design issue that I'm not sure how to approach. I kind of know the theory, but I have no idea how to approach it practically.

 

Here's the problem...

 

I have a load, my cultivator unit, that will be about 3' - 4' tall, maybe 12" to 18" in diameter and weigh between 20 and 40 lbs. The whole thing will be mounted on a lazy susan style turntable. The plan is to have a gear or pulley at the bottom that will be used with a hight torque stepper motor, and chain or belt, to rotate the cultivator. I'm using a stepper motor because they are pretty efficient and can be controlled very easily at very slow speeds. I want the rotation speed to be maybe 3 to 4 revolutions per day. A stepper would work well for this I think.

 

I have no idea how to properly size the motor. I see them speced at anywhere from 10s of oz-in to 1000s of oz-inches of torque. I get the concept of torque being rotational force. And that required torque has to do with acceleration time up to the desired RPM. But I have no idea how to relate this to my requirements.

 

I'm a 'puter software with some dangerous electronics knowledge guy! HELP!!! And feel free to tell me this just a stupid idea and I should be using a washing machine motor or something if that's the case.

 

For reference, here's a drawing of the rig. Note the drive at the bottom right. Please excuse the misspelled labeling. I haven't gotten around to correcting it yet. lol...

 

image

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  • Hi Rick, From your description and design it looks like all you will have to over come is the inertia of your cultivator and what ever friction there is in the lazy susan bearings. Since you are talking about a very low RPM (Only about 2 times as fast as the hour hand on a clock) and you do not have to have high accelerations in the lazy susan you will not need that great a torque. You can test your needs by measuring the radius of your drive gear and test to see how much force is required to turn the lazy susan at that radius. A stepper will not produce a continuous motion at these low RPMs and the frequency of your steps may be determined by the minimum step angle of the motor. Your gear ratio motor to lazy susan will also have to be taken into account. I am guessing that you will be gearing down to produce the low RPM and this will make it easier to use a low torque motor as the gear ratio will amplify the torque of the motor. I hope this helps and good luck.

    John

  • in reply to jw0752

    Try one of these.

    http://yourduino.com/sunshop2/index.php?l=product_detail&p=126

    You don't need to worry about the torque as they are geared, and almost unstoppable.

     

    John is quite right about using a stepper snce they are the best option for this slow speed.

     

     

    Mark

  • in reply to mcb1

    Thanks Mark,

     

    Are you thinking the one you linked to would do the job? $5.00 to do the job would be pretty nice indeed!

     

    Cheers,

    Rick

  • in reply to RWReynolds

    Rick 

    I can assure you it will turn your turntable easily.  image

    Being geared it doesn't freewheel, and if you check the specs its 64 :1.

     

    Terry has example code which shows it needs 2048 pulses for one shaft revolution.

    You have lots of options ...

     

    I'm off in a few hours so I'll be unable to respond but John should be able to assist with the mechanics/

     

    Mark

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