Motorcalc spreadsheet errors

[jimbo_cnc]

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.

[JAZZCNC]

Net result is I get different values for 3 of the 4 torque components.

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.!

[jimbo_cnc]

Not completely different I would hope.

The acceleration torques are not much influenced by alignment.

Besides I would build accurately :)

[JAZZCNC]

Not completely different I would hope.

The acceleration torques are not much influenced by alignment.

Besides I would build accurately :)

No I'm lying to you it will be exactly the same has the sheet says.!! . . . Crack On.

[jimbo_cnc]

I can't reply to that, because it makes no sense. 'Not completely different' does not equal 'exactly the same'.

[Jonathan]

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.