Calculations for weight-lifting motor...

  • #1
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Main Question or Discussion Point

The project I'm building involves a 12 V electric motor connected to a spindle lifting a 20kg weight. The radius of the spindle is 2cm, so the torque applied by the weight is 0,02m*20kg*9,8m/s^2, which gives me 3,92N*m. So, my 12 V motor needs to deliver 3,92N*m just to keep the weight steady. This is 40kgf*cm of torque.

I'm having trouble to select a motor appropriate for this task. First of all, the project that I'm designing will be placed on the chassis of a car, so it needs to be very trustworthy and robust (it will be exposed to all kinds of enviromental effects). Also, to lower costs, I don't want to design any gearbox to increase torque, so I think it would be better if the motor in question already included the gearbox. I searched for all kinds of 12 V gear motors, but haven't found anything within those limitations.

Could you give me any hints on how to proceed? Would designing a gearbox will be my only way out? Also, all DC motors that I've found are used primarily in robotics, automation... I'm not sure if this kind of motor is
recommended for this application.
 

Answers and Replies

  • #2
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Do you have a cordless screwdriver/drill ... They are around the power you are looking for ...you can easily test it by winding a cord around a drill and seeing if it will lift the weight ...such electric drills are often thrown away when the battery dies ...

You are correct not to try to add a gearbox onto a motor , best to buy a motor with a gearbox , this will not be waterproof .... better to by a cheap cordless drill , these are a little better with regard to the elements , and will probably be cheaper than buying a motor.
 
  • #3
Nidum
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A few key strokes will find you multiple sources for 12 V motors with gearboxes .

Before that though you need to properly identify the usage profile for your application .
 
  • #4
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Do you have a cordless screwdriver/drill ... They are around the power you are looking for ...you can easily test it by winding a cord around a drill and seeing if it will lift the weight ...such electric drills are often thrown away when the battery dies ...

You are correct not to try to add a gearbox onto a motor , best to buy a motor with a gearbox , this will not be waterproof .... better to by a cheap cordless drill , these are a little better with regard to the elements , and will probably be cheaper than buying a motor.
I will certainly give a look at that. Thanks!

A few key strokes will find you multiple sources for 12 V motors with gearboxes .

Before that though you need to properly identify the usage profile for your application .
Indeed, I've found some 12 V motors with gearbox, but most of them don't have the torque that I need. Most of these are small DC motors for robotics and automation.

The project I'm building will be exposed to environmental effects (sun, rain) so I need to think about some way to protect the motor from these effects.
 
  • #5
Nidum
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http://docs-europe.electrocomponents.com/webdocs/0093/0900766b800932a5.pdf

That is one possibility of many . You are unlikely to get a motor and gearbox that does exactly what you want .

Apart from ruggedness much depends on required output speed and the duty cycle .

Personally I would use a generously overrated motor and design my own gear train and housing .
 
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  • #6
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Personally I would use a generously overrated motor and design my own gear train and housing .
I've thought about designing my own gear train, but that would increase the cost too much.
 
  • #7
russ_watters
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The project I'm building involves a 12 V electric motor connected to a spindle lifting a 20kg weight. The radius of the spindle is 2cm, so the torque applied by the weight is 0,02m*20kg*9,8m/s^2, which gives me 3,92N*m. So, my 12 V motor needs to deliver 3,92N*m just to keep the weight steady. This is 40kgf*cm of torque.

I'm having trouble to select a motor appropriate for this task.
How fast do you want to lift it? That's pretty important too.
 
  • #8
178
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How fast do you want to lift it? That's pretty important too.
Probably something like 2cm/s. The speed is not a critical issue in the project
 
  • #9
CWatters
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So, my 12 V motor needs to deliver 3,92N*m just to keep the weight steady
It's not usually a good idea to "stall" an electric motor if that's what you are planning.
 
  • #10
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24VDC gear motors are available in the market with your requested torque
 

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