Star Adventurer belt conversion

[8472]

Hi,

To reduce the PE of my tracker, I'm toying with the crazy idea of replacing the three spur gears with a belt driven system.

There's no off-the-peg commercially available solutions, so I'm weighing up doing it myself.

I've stripped down an tuned mounts, including the SA previously, but never undertaken a belt conversion.

So, my question is, the gear arrangement is a 24T drive gear going to a 42T intermediate spur gear, to a final 37T spur gear connected to the worm. What two size belt and pulleys would I need to replicate the gear reduction ratio?

Thanks,

Kev

[newbie alert]

Belts will turn in the same direction, cogs turn in opposite directions.. I can be done but would require more work than a SA is worth

Many people belt mod other mounts, not seen a SA done thou, probably for the above reason

 

[malc-c]

From my experiments with the HEQ5 over a decade ago (long before Rowan came out with their belt drive kit) I was told that you can ignore the interim gear and work out the ratio by using just the other two gears.  So the worm is 37T and the motor is 27T so you could simply use that if pulleys of the same number of teeth are the same physical diameter as the gears.  It would seem that the motors have a lot of torque if the motor gear is only 10 teeth less than the worm gear.  One thing to consider is the clearance of the cover.  I had to form a spacer in order to clear the machined pulleys as the gears are naturally a lot thinner.   

The problem you are going to be faced is locating commercial made pulleys with the same number of teeth in order to make the mount compatible with the handset.  I opted to use EQMOD as the mount was in an observatory and could use standard ratios such as 4:1 by using a 60t on the worm and 15t on the motor and have EQMOD do the math.....  This is where Rowan Engineering stepped in as they could machine pulleys to give the same stock ratios and thus allow the mount to use the handset.

[8472]

Yes, I've just been told the intermediate gear can be ignored, so I've calculated the setup to be 1:1.54167.

As said, the interesting bit will be finding a set that will fit...

Cheers all

[newbie alert]

Beltingonline can supply many different versions of pulleys and adapt the bore size and even reduce the face width if space is the issue..

Pe comes from the worm

Edited April 18, 2022 by newbie alert

[8472]

23 minutes ago, newbie alert said:

Beltingonline can supply many different versions of pulleys and adapt the bore size and even reduce the face width if space is the issue..

Pe comes from the worm

Thanks for that.👍

I'm aware of the PE in the worm. Just thought maybe elimination of spur gear backlash may help, or is it an exercise in futility?

[newbie alert]

Just now, 8472 said:

Thanks for that.👍

I'm aware of the PE in the worm. Just thought maybe elimination of spur gear backlash may help, or is it an exercise in futility?

I can't see that it will work.. it won't be a case of buying pulleys and belts and slapping them on...  Can't see it's worth it,not on a SA anyway

[malc-c]

23 hours ago, newbie alert said:

I can't see that it will work.. it won't be a case of buying pulleys and belts and slapping them on...  Can't see it's worth it,not on a SA anyway

Adding a belt drive to a mount that has a gear train with intermediate gears does improve backlash to a point as you are removing one or more areas where the it occurs.  However I agree that there will be a lot of effort in sourcing suitable pulleys and machining them to fit, so the whole process may indeed not be worth the effort 

[newbie alert]

And the belts will turn in the same direction meaning the board will have to be either hacked or the wires reversed

[GTom]

Interested on this for an Adventurer GTI! Very capable little mount, would be great to eliminate backlash and reduce PE.

[Guest]

So it seems the gear assembly might be different from the azgti so reducing backlash via belts would be useful I think, but more in dec than ra though.

To put it in perspective, the azgti had an internal set of reduction gears mounted straight on top of the motor.  The output shaft came out of that asbly and connected to the worm via two equal tooth spur gears.  The problem was that internal gear assembly allowed a lot of shaft play side to side that no amount of backlash adjustment of the two spur gears could fix.  So make sure this assembly has nothing like that.  The skyguider pro on the other hand had a belt assembly that worked much like you plan to do, and it had very little backlash as a result.

Another observation.  If you remove the intermediary gear and just drive with a belt you don't have to worry about reversing directions as far as I can figure out.  The intermediary gear reverses the direction of the third gear so it turns in the same direction as the first, just as if you'd be using a belt.