T-Rex and Vixen Porta Mount Owners

[sharpiel]

I have a JMI Train and Track unit bought from a fellow IIS'er. It's my intention to build a wooden alt-az mount for my Meade 12" OTA for visual use.

I need to work out the gearing ratios so the unit tracks at the right rates for me. The JMI Train and Track I have was made for the T-Rex Mount and works also on the Vixen Porta Mount.

Asking owners of either mounts or anyone knowledgeable out there what the manual gearing reduction rates are on both axis of either/both mounts are so I can replicate that.

Cheers

[LewisM]

All I could find Les is that:

Elevation Axis incorporates 120 tooth Worm Gear Set
Rotation Axis incorporates 120 tooth Worm Gear Set

Not that that helps any with reduction rates I guess.

[sharpiel]

Thanks Lewis. It's a start. For the ratios I'd still need to know how many full 360 degree rotations of the worm results in one full 360 degree rotation of the gear itself.

[Saturnine]

One worm rotation equals 1 tooth pitch on the ring gear so 120 rotations of the worm equals 1 full rotation of the ring gear = 360 deg.

[Saturnine]

So 1 rev. of the worm = 3 deg. axial rotation

360 deg divided by 120 T

[sharpiel]

Excellent. So the reduction is 120:1. Am I right in reading it that way?

[Saturnine]

That's correct, you're reading it right.

[sharpiel]

Thanks both Lewis and Jeff.

[AstroApprentice]

Avalon Instruments motor kits for T-rex state a gear ratio of 720.
http://www.avalon-instruments.com/products/motor-kit

[thebonz]

I just checked my t-rex and to complete a 360 degree rotation in Az I had to rotate the worm 180 times.
John

[sharpiel]

Jason I just looked at the link. It does say 720...I wonder to what specifically it refers? Maybe it accounts for further ratios between the motor and its attachment to the axis pinions..? :question:

John, thanks for doing that test. To me that is fairly definitive. Could you confirm that on both axis for me please?

I wonder if someone with the Vixen Porta Mount could do the same test for me on both axis please.

[Tinderboxsky]

The belt drive shown in the Avalon website image looks like a 4:1 reduction drive. If so, the the total reduction involved will be 4X180=720:1 as quoted on the website.
I have TRex and a Vixen Porta mount - I’ll check mine for you.

[Tinderboxsky]

Les, just checked my mounts:
TRex - 180 revolutions of the worm for 360 degree rotation as John has reported
Vixen Porta Mount - 120 revolutions of the worm for 360 degree rotation.

[sharpiel]

Steve. That is absolutely awesome. Thank you so much. I assume the revolutions are the same for both altitude and azimuth axis for the respective mounts?

[Tinderboxsky]

Yes, you would expect so given the housings are the same size.
John checked AZ and I checked ALT for the TRex, so both the same. Just double checked and both the same for the Porta Mount.

[sharpiel]

Excellent. Thanks everyone for your help. Great community as usual

:thumbsup::thanx: