How do you calculate weight from current?
How do you calculate weight from current?
(OP)
How do you measure the weight of a roller coaster car being pulled up the chain-driven lift hill? I know the weight of the loaded train is directly proportional to the power needed to pull the train up the lift hill so I suspect you can measure the current draw from the motor but beyond P=IV I am not sure what formulas exactly you would use to get the weight or mass (M) of the train from current (I). Any ideas?





RE: How do you calculate weight from current?
David Castor
www.cvoes.com
RE: How do you calculate weight from current?
If you want to get more accurate figure in the losses between electrical power consumed and mechanical powered delivered to lift the mass.
RE: How do you calculate weight from current?
http://excelspreadsheetshelp.blogspot.com
RE: How do you calculate weight from current?
If you do not know the formula but know there must be one, then I suggest looking in some of the popular Engineer's Toolbox type websites that sell you such things, and look for a conveyor HP calculator. It will ask for the load and the angle of inclination, the two most important issues. It may ask for other things like belt width etc, which factors in friction, but for the most part whatever you use for a conveyor belt formula will account for a lot more friction than a roller coaster would, so it will estimate high in terms of the power requirement.
Here is one resource I know of that sells one.
http://www.pwr-tools.com/contents.html
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RE: How do you calculate weight from current?
A
RE: How do you calculate weight from current?
so on I think the weight is not enough!
I want, I can, I do.
RE: How do you calculate weight from current?
RE: How do you calculate weight from current?
Uh, your OP said (I paraphrase) "how do I measure the weight, knowing current"
Zeus answered (correctly) that you calibrate it using a known weight of the car and measuring current for that weight. Do it again for another, different known weight. You should then be able to interpolate between those two numbers to determine other, unknown weights, knowing current alone.
To do it any other way you must include all the effects, including the ones you listed, the ones Zeus listed, and the other effects that neither of you thought of...
RE: How do you calculate weight from current?
I beleive many if not most large coasters are one-off designs to give the amusement park a unique ride.
If this is for something like setting a braking force further down the track then I would do tests as suggested once the coaster is built. You can start with an initial "best guess" and fine tune it using a few different weights during test runs.
If it is required before construction then you'll have to calculate the force required to pull the train up the hill and then calculate the corresponding torque at the motor shaft. Using the motor data, it should be fairly simple to calculate the current corresponding to the weight. Hopefully, you have some prior data from other designs to help pin a number on the expected losses.
RE: How do you calculate weight from current?
http://excelspreadsheetshelp.blogspot.com
RE: How do you calculate weight from current?
Measure the current with each of these cases. This will give you the true weight verses current demand.
As btrueblood sez, just interpolate between these values and you will have a very close weight/amps correlation.
A side benefit will be the ability to track wear and adjustment shifts. During the morning dry runs keep a log of the empty cars currents. If they change dramatically or you see them trending it will be useful information.
Keith Cress
kcress - http://www.flaminsystems.com
RE: How do you calculate weight from current?
You posted it is a DC motor so you likely already have a DC motor controller on it. That controller is also likely able to give you either an analog or communications output for percent load which you can use as feedback to the coaster controls.
RE: How do you calculate weight from current?
Yikes, your application sounds dangerous. How accurate do you need to be in the weight measurement?
RE: How do you calculate weight from current?
then run it in the real state by virtual masses and calibrate your system.
And I agree with BrianE22 in other wise its really dangerous!!
I want, I can, I do.
RE: How do you calculate weight from current?
RE: How do you calculate weight from current?
I want, I can, I do.
RE: How do you calculate weight from current?
RE: How do you calculate weight from current?
I want, I can, I do.