Sunday, 18 August 2019

Parametric (re)model for motor housing

What up, Fatty?
So, one or two improvements came to mind last time round. I've been busy building an ensuite bathroom in the house, so had little in the way of serious workshop time. 

A couple of weeks ago I set to on the motor / drive housing (yet again), hopefully for the last time. There's only so much you can bugger about but when you sit back and look at what I've created so far, although it looks pretty nice, when you ask why certain features are the way they are - and more to the point - what purpose they serve, I must admit there are one or two legacy features that complicate the design and its production while adding no obvious functional benefit. That's one of the problems with humans.


The housing is currently dimensioned to suit the Leadshine closed loop stepper I bought several years ago (iSS57-20). I'm aware that there is no clear standard for the flange and register design, despite all the NEMA etc stuff. So the chances are that most other motors of this approximate size would require different dimensions. I have also be buggering about with different pulley and bearing sizes and belt lengths. So why not use "User Parameters" to control the dimensions in Fusion 360? That way, it should be possible to change some of those variables without having to dive deep into the design history to find where they are defined. Obviously there will be a practical limit on the range of variation possible but nonetheless I should be able to accommodate some.

At this point, The Stupid Fat Bloke got into the CAD seat and predictably got rather carried away, trying to parameterise(?) almost every possible dimension near the thing, based on a single master sketch. Obviously that was never going to work, due to the sheer number of lines and constraints at play. This became evident when it came to creating extrusions etc from the master sketch. And as for the idea of creating offset shapes from chains of segments, forget it! Some happy(?) medium exists between a single master sketch and a whole series of sketch / extrude / sketch / extrude operations.

Here's a "middle way" - a fair degree of parametric dimensions for the core model, which will be extruded and then modified later:

And an initial parameters table:

A bit more buggering about...

...and this is what I've got now. Sort of simpler in many areas.

Top view:

It's mostly parameter driven and has lost quite a few silly (unnecessary) features. I need to finalise the key measurements such as the distance of the ballscrew from the spindle (currently 50mm but almost certainly an imperial 50.8mm?) and the motor dimensions. A couple of features still missing such as a mans of fixing the lid. Otherwise, seems like a reasonable result for now.

I've also reduced the bearing size to a 4200 (30x14x10 double row), which gives me more modesty space between the bearing and the quill, while still having plenty of margin on the max loadings etc. Combined with an 18t driven pulley and a 10t driving (motor) pulley, I've reduced the belt length. This in turn reduces the size of the housing slightly. 

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