Calculating Speed for a Mechanical Dolly Driven by Electric Motors

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Discussion Overview

The discussion revolves around calculating the speed of a mechanical dolly driven by electric motors, specifically focusing on the relationship between motor specifications, sprocket sizes, and wheel dimensions. Participants explore the necessary calculations to determine the appropriate sprocket sizes for achieving desired vehicle speeds.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant inquires about the calculation of speed for a dolly driven by two electric winch motors, mentioning the motors' ratings and drum size.
  • Another participant suggests that torque can be calculated from the motor rating and drum diameter, emphasizing the need to determine the RPM of the drum to find vehicle speed.
  • A different participant mentions that knowing the horsepower or kW can aid in calculating speed.
  • The original poster describes their plan to attach sprockets to both the winch drum and the wheel shaft, raising concerns about the ratio of sprocket sizes.
  • The original poster calculates the RPM of the drum and the wheel, concluding that both RPMs are roughly equal, suggesting that the sprockets must be the same size.
  • Another participant confirms the original poster's reasoning about the sprocket sizes being the same due to matching RPMs.

Areas of Agreement / Disagreement

Participants generally agree on the need to calculate RPMs for both the drum and the wheels, and the conclusion that the sprockets must be the same size if their RPMs match. However, there is some uncertainty regarding the specifics of how the motors will drive the dolly and the exact calculations involved.

Contextual Notes

There are unresolved details regarding the method of connecting the motors to the wheels, and the calculations depend on assumptions about the motor specifications and desired speeds.

fanning21
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Hi there,

I have recently been working on a project that involves building a mechanical dolly that is driven by 2 electrical motors.

I have decided to use 2 electrical winch motors which each have a rating of 5700kg and a drum size of diameter 64mm

My question is, how do I calculate the speed of the vehicle if I am planning on using 18" wheels.

Do i need to calculate the rotational speed of the drum first?

I need this information in order to decide which sized sprockets I am to use.

Thanks!
 
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Using the rating and the drum diameter you can find out how much torque it will produce (you'd only need this to confirm that the motors are strong enough to power your dolly for a certain vehicle weight and/or certain incline). You'll have to find out what the rpm of the drum is either via the description or by testing it out. You know the wheel size and you'll have to decide what vehicle speed you want so you can pick out the sprocket based on that. Or if there is a maximum sprocket size that you can put in your design or that you wouldn't want to exceed you can choose than to find the vehicle speed. I'm a little confused about how exactly the motors will be driving the motorized dolly. Are you going to attach sprockets to the wheel shaft and the motor shaft? Or are you going to attempt to make the wench cable go around a pulley to turn the wheels? Or something else? Maybe a simple drawing would help.
 
If you have the horsepower/kW you can calculate the speed.
 
Thank you for the quick response, and sorry if my explanation was not too clear!

My plan was to attach one sprocket to the winch drum and another one to the shaft in order to drive the wheel..

My issue was deciding on the ratio of the sizes of the two different sprockets. I first calculated the RPM of the drum using the diamater and line speed. Then I calculated the RPM of a 19" wheel with a speed of 3 km/h

Basically both RPM's are roughly 33rpm which means that both sprockets must be the same size!

Does this make any sense??
 
fanning21 said:
Thank you for the quick response, and sorry if my explanation was not too clear!

My plan was to attach one sprocket to the winch drum and another one to the shaft in order to drive the wheel..

My issue was deciding on the ratio of the sizes of the two different sprockets. I first calculated the RPM of the drum using the diamater and line speed. Then I calculated the RPM of a 19" wheel with a speed of 3 km/h

Basically both RPM's are roughly 33rpm which means that both sprockets must be the same size!

Does this make any sense??

Yup, that makes sense. The sprockets would be the same size since the rpms wanted for the wheel shaft and what the winch produce are the same. Good luck with your project.
 

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