On Sunday 21 March 2021 16:16:59 Viesturs Lācis wrote:
> otrd., 2021. g. 26. janv., plkst. 19:26 — lietotājs andy pugh
>
> (<bodge...@gmail.com>) rakstīja:
> > You have two internally toothed gears and a double-height
> > flex-spline. The gears have 202 and 200 teeth, the flex-spline has
> > 200.
> > That means that the flex-spline is static relative to the 200 tooth
> > gear, but moves the 202 tooth gear.
>
> My apologies if I missed it explained somewhere in this thread, but I
> have a question about the design of those two gears with internal
> teeth:
> If I understand correctly, pitch diameter is equal for both gears. But
> the number of teeth is different. IMHO it should affect the pitch of
> the teeth. Is that correct? Does it mean that there are 2 different
> rows of teeth on flexspline - for each of the internal teeth gears?
> There was a suggestion to use timing belt as flexspline, so that would
> mean that teeth pitch is equal on both internal teeth gears, but then
> I do not understand, how to get equal pitch diameter with different
> number of teeth...
>
> Viesturs
>
I don't think you can call me an expert on openscad but the only thing I
changed to go from 60 to 62 was the incremental rotation I used the
place the teeth, which are in fact triangles made from passing a $fr=3
to the cylinder code, getting an equilateral triangle whose tips are the
diameter passed to cylinder. The roots of the tooth overlap changes very
slightly which changes the pitch diameter by a miniscule amount that I
haven't tried to compensate for. There are at least 3 ways to go about
assuring a consistent pitch diameter but that code is a bowl of noodle
soup already. Ideally, the size of the cylinder that forms the tooth
should change too, but my code doesn't do that. That would also change
the inner circle diameter, but I jusr sized that to assure there weren't
any floating parts of the tooth base where it sits on the inside face of
the outer shell.
I hope that makes sense. Attached for your entertainment is the .scad
that generates the outer rings, I switch tooth counts by having all
three possibilities in there with 2 commented out. Don't bust a gut
laughing at it... But it seems to work ok.
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
// new example, using a low ratio harmonic drive floating
// splined belt with 60 teeth.
// s/b 30/1 when finished.
$aa=69.0000000; // was 70.00000000 a blond one too big
$xx=9.750000000;
$dd1=111.40000000;
$dd0=120.00000000;
$fx = ([ 360.00000000 / 60.00000000 ]); // arc of circle per tooth, works but...
// overall span of armature plus bearings equals 96.6mm's
$fr = [ 0.00000000]; // establish its storage
echo ("10 ", $aa, $xx, $dd0, $dd1, $fr, $fx) ; // echo? yes, once
difference() { // outside smoother, room for bolt holes
cylinder(d=$dd0, h=$xx, $fn=360); //outer is fussy
cylinder(d=$dd1, h=$xx, $fn=180); //but the inner isn't
}
// don't forget the bolt holes!!!
// for 6.00000 we got 60 teeth, for 62 teeth inc is 5.8064516129
// those 60 teeth rendered at 3.69mm peak to valley
// use this "for" for 62 teeth
//for($fr=[ 0.00000000: 5.8064516129 : 360.00000000 ]){ //can't pass $fd to
this for, why?
//use this "for" for 60 teeth
for($fr=[ 0: 6.000000000 : 360 ]){
//use this "for" for 58 teeth
//for($fr=[ 0 : 6.20689655172 : 360 ]){
//cylinder(h=11.75, d=8, center=true);
rotate([0.00000000, 0.00000000, $fr]) // works, finally
// this below works, but again, can't pass a var to translate
// what the hell???????
//
translate([54.05000000, 0.00000000, 0.00000000]) // mv x only
scale(v= [.1000000, .1000000, 1.000000]) // might use a small xy
// differential here to improve tooth fit.
rotate(180) // same here, using $var's doesn't work here or for
// cylinder. switch rotate on for outers and readjust sizes
cylinder(d=$aa, h=$xx, $fn=3); // make thick triangle
}; // switch h=9.500 for outer rings
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