How to spec a motor for this floor testing system?

  • #1
ktheslabguru
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I am designing a system to test floors, called the "Robinson-Type Floor Test". I have the basic design below, but I'm having trouble determining how exactly to spec the motor here. The large pulley on the rotary shaft is 12in in diameter and the small pulley on the motor is 3in in diameter. At most, the carriage will be holding 900 pounds (300lbs on top of each wheel). The wheels underneath the carriage will be hard rubber or steel. The surface that the wheels will be rolling on will be various different smooth tiles. The pulleys are heavy-duty v-belt pulleys. The carriage (the assembly) needs to rotate at a constant 15±0.5 RPM.

The distance from the center of the base plate to each wheel is 15in, and the rounded corners of the triangular base plate have 6in radii. The base plate is a 1/2in thick hot rolled steel plate. The rotary shaft itself is 60in tall, to give a sense of scale here.

Any advice? Trying not to go overkill and spend way too much on a motor, but I also don't want to buy a motor that's too weak.

Help is appreciated, thank you!


Mockup For Torque Calcs.jpg
 
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  • #2
Welcome to PF.
Since the RPM is specified, only the torque is needed to compute the power required. The torque will depend on the highest frictional drag floor you will need to test. For that reason, you can use the same power rated motor as any other similar tester. The power needs to be sufficient, excess power will increase the range of the machine to test softer floors.
 
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  • #3
ktheslabguru said:
The wheels underneath the carriage will be hard rubber or steel. The surface that the wheels will be rolling on will be various different smooth tiles.
There are two ways to handle this problem.

- you can give an estimate to the rolling friction, then calculate a required force based on the expected load: at the end of the day you will get a power requirement which you will double for safety margin, and so you will have it with the certainty of a decent guesswork, for the price of a never-again-used math exercise. And still, all the numbers can be wrong, of course.

- you can check the datasheets of electric trolleys with some similar-looking wheels and 1000kg load capacity: what kind of motor do they use? ....and then you can choose a bit bigger one.

I would say something around 0.8-1kW. With good cooling.
 
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  • #4
ktheslabguru said:
Robinson-Type Floor Test
Perhaps you could give us a link to an actual explanation of what the test actually involves. All I can find is websites that assume you already know what it's all about. Is it a strength test or a test of sound insulation? Cheers
Also, your diagram seems not to include bracing to improve how that single rod would behave during 'violent?' oscillations. Could you comment?
 
  • #5
sophiecentaur said:
Is it a strength test or a test of sound insulation?
https://www.astm.org/c0627-18e01.html
"1.2 This test method is intended solely for evaluating complete ceramic floor tile installation systems for failure under dynamic loads and not for evaluating particular characteristics of ceramic tile, such as abrasion resistance. This test method does not claim to provide meaningful results for other than evaluating complete ceramic floor tile installation systems."

This describes the process, with a 3/4 HP motor.
https://tcnatile.com/wp-content/uploads/2022/08/Heres-to-you-Mr.-Robinson.pdf
 
  • #6
Baluncore said:
This test method does not claim to provide meaningful results for other than evaluating complete ceramic floor tile installation systems."
I'm not too familiar with the specs that are used for building installation but it strikes me that you would need to buy the equipment for testing a floor. Making your own Robinson unit would not give a consumer any redress for a floor that was thought to be 'unsatisfactory'. You could probably make a near copy of an available unit and save a lot of money but would its results be accepted in any complaint or action?

The motor characteristics would be the least problematic to specify.
 
  • #7
ktheslabguru said:
I am designing a system to test floors, called the "Robinson-Type Floor Test".
Then you NEED a copy of the current ASTM standard that was linked in Post #5. That ASTM standard specifies how to design the Robinson test fixture. You need to build the test fixture exactly to the ASTM standard in order to have test results that other people will accept.

The image below was copied from an obsolete copy of that ASTM standard. It looks nothing like the sketch in Post #1. You need to start over with a current copy of the standard, which costs only $75.00. That cost is cheap compared to the cost of the test fixture, and extremely cheap compared to the cost of building a useless test fixture. Note that the ASTM standard tells you exactly what motor to buy.
Robinson test.jpg
 
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  • #8
jrmichler said:
in order to have test results that other people will accept.
You need to come to terms with this. Annoying, perhaps but . . . . .
 
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  • #9
ktheslabguru said:
I don't believe posting a screenshot of the latest standard would be legal.
Why ever would it not be, as long as you acknowledge the source?
As far as I can see, your problem was to post 'sketch' diagram (albeit, produced with an up-market method) which is actually nothing like the real Robinson gear. So your post has no credibility because the image implies that is your basic design, which is not very convincing (even for a humble Electronics engineer)..

If you want an answer to your question, why not ask for a price and spec from a manufacturer? The user / maintenance manual will have the motor spec for sure. If you believe you can save on cost then that's up to you.
ktheslabguru said:
just wanted to look for some assistance first
I'd say that the 'assistance' on the thread is highly appropriate, given your initially supplied information.
 
  • #10
ktheslabguru said:
The exact motor is not specified in the standard - just the requirement for turning the assembly at a constant 15±0.5RPM with, at most, 900lbs distributed evenly on each of the three wheels.

Will likely end up purchasing an over-spec'd motor and going down from there, but just wanted to look for some assistance first.
3/4 HP was specified, and there is no reason why that has changed. You will need to select a gearbox, chain or belt reduction to give 15 RPM. The line frequency will determine the induction motor RPM.
 
  • #11
Baluncore said:
3/4 HP was specified, and there is no reason why that has changed. You will need to select a gearbox, chain or belt reduction to give 15 RPM. The line frequency will determine the induction motor RPM.
Noted, thanks.
 

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