Why cant i get the same torque from a gear drive as apposed to a chain drive?

In summary, the geared drive system will not be able to lift the load as easily as the chain drive with a 3.7x1 ratio. The gears increase the rotational inertia in the driveline, and the stiction force when starting the load.
  • #1
volie1
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I am trying to lift a load with a drill motor. I have a chain drive with a 3.7x1 ratio - 13 teeth on the drive gear with a 2.5" diameter and 48 teeth on the driven gear with a 7.75" diameter. It lifts the load easily.

I also have a geared drive (no chain) with a 4.0x1 ratio - 16 teeth on the drive gear with a 1" diameter, and 64 teeth on the driven gear with a 4" diameter. The latter won't begin to lift the load. Whats wrong?
 
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  • #2
Are you sure the gears aren't binding due to improper mesh? Otherwise other than friction and binding I don't see the problem.
 
  • #3
I can turn the geared drive freely with my fingers using my other hand to apply a load
 
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  • #4
Do you think the gears increase the rotational inertia in the driveline? Or the stiction force when starting the load? These two factors impact the sufficiency of starting torque.
 
  • #5
I know this sounds painfully obvious, but we all forget/ignore the obvious sometimes...
The drive gear on the geared system (assuming there is no intermediate gear) will have to turn in the opposite direction of the chain-drive system to move the load in the same direction. You will need to reverse the drive gear rotation when switching systems.
 
  • #6
I did reverse the direction of the motor for the geared unit, if I get it to work I will install an intremediate gear. System Theory you are above my head on that one I do know both units are starting from a standing state.
 
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  • #7
Do you know the mass of the load? Are you lifting it with a cable on a drum? If so what is the drum radius? How thick are the gears you're using and are they heavy compared to the chain and sprockets? (Are the sprockets relatively heavy or light?)
 
  • #8
There's not enough information. You've given us enough information to calculate relative torques, but not linear forces. How is the torque at the driven gear being converted into a linear force to lift the load?

If both the 7.75" sprocket and the 4" gear are turing the same diameter drum, then there's a second torque multiplier involved, and this torque multiplier would be larger for the 7.75" sprocket.

Lastly, chain drive losses are less than gears. Effenciency might be about 92% with chain, and about 87% with gears.
 
  • #9
Based on what you all are saying, could my problem be the difference in the sprocket diameters and the total number and size of the gear teeth compared to the chain sprocket? If that is probably the cause I will buy a new pair of gears closer related to the chain drive. The load is lifted with a cable drum I will find the diameter if it is now needed. The approximate weight of the load is 200-300 lbs.
 
  • #10
As Jeff said the radius of the drum on the take-up cable is relevant to the torque leverage. It should be possible to caculate the minimum starting torque required if the drum radius is known.
 
  • #11
I used a torque wrench to find the starting torque. It took 250" lbs to initiate any movement of the load. I measured the max torque on my drill motor and it was approx. 150" lbs with a fully charged battery. It seems that a four to one ratio should be sufficient but you may know additional forces that apply. I guess I will just go to about a six to one ratio, do you think that would work? Thanks again for all your help
 

1. Why is the torque output different between a gear drive and a chain drive?

There are several factors that contribute to the difference in torque output between gear drives and chain drives:

  • Size of the gear or sprocket: A larger gear or sprocket will have a larger radius, resulting in a greater mechanical advantage and higher torque output.
  • Number of teeth: The more teeth a gear or sprocket has, the greater the contact area and the higher the torque output.
  • Friction: Chain drives typically have more friction than gear drives, which can reduce the overall torque output.
  • Design and material: The design and material of the gears or sprockets can also affect the torque output.

2. Can a gear drive ever have the same torque output as a chain drive?

Yes, it is possible for a gear drive to have the same torque output as a chain drive. This can be achieved by using gears or sprockets with the same size, number of teeth, and material. However, this may not always be practical or feasible depending on the specific application.

3. Do gear drives or chain drives have higher torque output?

Neither gear drives nor chain drives inherently have a higher torque output. The torque output depends on various factors such as gear/sprocket size, number of teeth, friction, and design/material. In some cases, a gear drive may have a higher torque output, while in others a chain drive may have a higher torque output.

4. Why do some applications use gear drives while others use chain drives if the torque output can be different?

The choice between a gear drive and a chain drive depends on several factors such as the required torque, speed, precision, and cost. In some applications, a gear drive may be more suitable due to its higher torque output and precision, while in others a chain drive may be preferred for its lower cost and flexibility.

5. Can I increase the torque output of a gear drive by adding more gears?

No, adding more gears to a gear drive will not necessarily increase the torque output. In fact, it may even decrease the torque output due to the increased friction and complexity. The torque output of a gear drive depends on various factors, as mentioned earlier, and simply adding more gears will not always result in a higher torque output.

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