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Unread 10-11-2017, 07:28 AM
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StephenKohnle53 StephenKohnle53 is offline
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Torque needed

I have a project for engineering where I need to lift a chain by using a 2 volt motor to lift it. It does not matter how fast it lifts the chain all I need is to be able to lift it and if I can then and only then may the speed matter. If I get a full lift and someone else does then whoever was faster gets more points.

Any ideas on how to increase torque without changing the motor at all. I do know that if I increase the size of the lift gear it will increase the torque and the smaller the drive gear the more torque, any other ideas and what gear ratios should I use.
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Unread 10-11-2017, 07:38 AM
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Re: Torque needed

You'll need to figure out some more information before you can determine the best gear ratio for lifting the chain as quickly as possible. First, what is the weight of the load you'll be lifting? Second, what is the power output of the motor? Voltage is not a measurement of power, so you'll need to figure out how much power the motor can output. Once you get that info, you can start to figure out what's next.
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Unread 10-11-2017, 07:41 AM
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Re: Torque needed

Quote:
Originally Posted by StephenKohnle53 View Post
I have a project for engineering where I need to lift a chain by using a 2 volt motor to lift it. It does not matter how fast it lifts the chain all I need is to be able to lift it and if I can then and only then may the speed matter. If I get a full lift and someone else does then whoever was faster gets more points.

Any ideas on how to increase torque without changing the motor at all. I do know that if I increase the size of the lift gear it will increase the torque and the smaller the drive gear the more torque, any other ideas and what gear ratios should I use.
Do you have to use a specific 2 volt motor or just a 2 volt motor? Do you have the spec sheet for the motor?

What is the weight of the chain?

Edit: Here are two resources you can use to learn more about motors and gearing.

2007 FIRST Conference on Robot Drive System Fundamentals

Ken Stafford (Team 190 mentor and professor at WPI) talking about motors
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Last edited by ATannahill : 10-11-2017 at 07:48 AM.
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Unread 10-11-2017, 07:51 AM
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Re: Torque needed

Quote:
Originally Posted by StephenKohnle53 View Post
I have a project for engineering where I need to lift a chain by using a 2 volt motor to lift it. It does not matter how fast it lifts the chain all I need is to be able to lift it and if I can then and only then may the speed matter. If I get a full lift and someone else does then whoever was faster gets more points.

Any ideas on how to increase torque without changing the motor at all. I do know that if I increase the size of the lift gear it will increase the torque and the smaller the drive gear the more torque, any other ideas and what gear ratios should I use.
Usually if you want to increase torque without changing the motor, as you mentioned changing the drive gear ratio is a good idea. The larger the gear ratio, the higher the torque, however the speed decreases. If that still doesn't give you enough torque then you would need to use a gearbox. I can't comment about what the recommended ratio should be because you need to know the minimum torque and motor specs to get that information.

There are many websites that allow you to input information such as motor torque, rpm, and a gear ratio and it will give out the output torque and speed. We used them a lot during Steamworks when working on our climbing mechanism.
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Unread 10-11-2017, 07:52 AM
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Re: Torque needed

Given enough gear reduction, any motor can lift any load. It's just a matter of how fast.

To solve this problem for optimal speed, you will need the specifications of the motor (free speed, stall torque, free current, stall current). You will also need the size of the load.

You say you are lifting a chain. Is the chain on a sprocket? How much weight is on the chain (including the chain itself)? This linear force (weight) can be converted into a torque once we know the size of your sprocket (effective diameter - this can be approximated by measuring it, or you can get the exact diameter with the number of teeth and the pitch of the chain).

When designing your reduction, you probably want to opt to do so at about 50% of stall torque (or a little less) - this is the "max power" of a DC motor, and thus where you will get the most speed / torque at the same time. This is assuming your motor will not burn out due to heat buildup, which isn't necessarily a given, it depends on the motor.

This should help you get started.
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Unread 10-11-2017, 07:56 AM
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Re: Torque needed

I do not know the output power of the motor, I will try to get that, my teacher does not have the chain yet so I will get it tomorrow to tell you the weight. Is there a way to measure the power output of a motor. (As you can guess I know very little about engineering). I think I have a voltmeter at home that can measure power as well so I will try that after school.

Also the focus is to lift the chain not necessarily quickly that is a secondary objective.
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Unread 10-11-2017, 08:12 AM
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Re: Torque needed

Increasing voltage will increase torque and speed while allowing you to use the same motor. 2x the voltage= 4x the output power.

Little hobby motors will happily run overvolted for a while.

However overvolting should not be used as a replacement for adequate gear reduction.
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Unread 10-11-2017, 08:18 AM
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Re: Torque needed

Quote:
Originally Posted by StephenKohnle53 View Post
Is there a way to measure the power output of a motor. (As you can guess I know very little about engineering). I think I have a voltmeter at home that can measure power as well so I will try that after school.

Also the focus is to lift the chain not necessarily quickly that is a secondary objective.
If you know the model number for the motor (sometimes listed on the side) and go to a seller's website like Andymark or McMaster Carr usually they would have information on the motor such as the power and stall torque.
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Unread 10-11-2017, 08:53 AM
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Re: Torque needed

If you can lookup or figure out the motor specs (i.e. free speed, stall torque, free current, stall current), you can use the Mechanism Ratio part of my spreadsheet to calculate the gear ratio needed. You can manually enter the motor specs*, enter the radius of the sprocket (when you get it) and the load it needs to lift. Then you can figure out the gear ratio needed to get max power (fastest speed), max efficiency, a certain linear speed, or a certain current draw.


*The spreadsheet assumes that the motor specs are at 12V, so if the specs are at 2V you should leave 12V in voltage applied.
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Unread 10-11-2017, 08:55 AM
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Re: Torque needed

Quote:
Originally Posted by StephenKohnle53 View Post
I have a project for engineering where I need to lift a chain by using a 2 volt motor to lift it. It does not matter how fast it lifts the chain all I need is to be able to lift it and if I can then and only then may the speed matter. If I get a full lift and someone else does then whoever was faster gets more points.

Any ideas on how to increase torque without changing the motor at all. I do know that if I increase the size of the lift gear it will increase the torque and the smaller the drive gear the more torque, any other ideas and what gear ratios should I use.
So the motor is given to you, is the power supply given to you as well? Is this purely a mechanical gear ratio problem or do you get to adjust the inputs (voltage + current into the motor) as well as outputs (some type of mechanical advantage translating to lift of chain)?
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Unread 10-11-2017, 12:43 PM
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Re: Torque needed

Well if speed is a non-issue I would say that you could use this.
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Unread 10-11-2017, 12:55 PM
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Re: Torque needed

Quote:
Originally Posted by Munchskull View Post
Well if speed is a non-issue I would say that you could use this.
One could argue hat using this WOULD lift the chain at some point in existence. One would be technically correct, which is the best kind of correct.

But, one would still not meet the goal of the assignment, which is (presumably) to lift the chain BEFORE the heat death of the universe.
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Unread 10-11-2017, 01:25 PM
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Re: Torque needed

sound like a fun problem.

If we could get an idea of the size of the motor, we might be able to offer more useful suggestions.

I wonder if a very simple winch would work? ie. extend the motor shaft with a thin rod or tube, and tie a piece of string on to the chain and tape it to the shaft, rod, and wind er up.
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Unread 10-11-2017, 02:00 PM
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Re: Torque needed

Like others, you need to gain more information about the test configuration. The torque required is one piece of the problem and it may be that you will have to experiment to determine the torque.

Some other information you need to collect. What is the overall system configuration? This should include the power supply with voltage, how the motor is mounted, how you interface to the motor spindle (at a minimum the shaft diameter).

Do you have access to the test setup in advance?

What tools or equipment will the teacher supply? The motor? Gears or pulleys that interface to the motor? Chain or Belt to connect the gears or pulleys? The power supply? Method to control power delivered to the motor? A volt meter? A scale?

How much does the chain weigh, how is the chain lifted and how far do you lift the chain.
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Unread 10-11-2017, 02:22 PM
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Re: Torque needed

Quote:
Originally Posted by MrForbes View Post
sound like a fun problem.

If we could get an idea of the size of the motor, we might be able to offer more useful suggestions.

I wonder if a very simple winch would work? ie. extend the motor shaft with a thin rod or tube, and tie a piece of string on to the chain and tape it to the shaft, rod, and wind er up.
Take this a little further, and add a snatchblock pulley setup to increase torque.
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