Thread: Motorcalc spreadsheet errors
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10-03-2015 #1
I can't find where I downloaded it from now, so I'll put this in General.
Here's what I found. Perhaps someone can check this over.
I deconstructed the spreadsheet and simplified it, getting the same results.
Then I looked at the equations.
I think I have found these errors:
1. rotor inertia conversion error. Should be 1e-7 conversion not 1e-8.
2. torque to accelerate the gantry should include the ballscrew efficiency.
3. <deleted> my error
Net result is I get different values for 2 of the 4 torque components.Last edited by jimbo_cnc; 10-03-2015 at 04:17 PM. Reason: removed 1 non-error!
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10-03-2015 #2
Ye and then in real world use the Net result will be another complete different reality.!! . . . Why because of the stuff like build inacuurecy and friction etc not bearing any resemblence to what the limited data in those sheets work upon.! . . . . So IME treat it as a very rough guide only before wasting too much time on it.!
Last edited by JAZZCNC; 10-03-2015 at 03:21 PM.
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10-03-2015 #3
Not completely different I would hope.
The acceleration torques are not much influenced by alignment.
Besides I would build accurately :)
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10-03-2015 #4
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10-03-2015 #5
I can't reply to that, because it makes no sense. 'Not completely different' does not equal 'exactly the same'.
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10-03-2015 #6
This is the thread:
http://www.mycncuk.com/threads/1524-...2489#post42489
You have correctly identified the errors.
I made my own version, as a script posted here. I added calculations for efficiencies, friction in different parts and the pulley inertia's. The latter makes a big difference... after including those things I've found it to be a good match with reality.
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