ANYONE???? Reduction ratios in Harmonic mounts

[Nikolas]

I'm confused and not very mathematically technical so hopefully someone can answer this for me in laymans terms
I was looking at harmonic mounts and came across this comparison. They are made by Umi (could be any manufacturer really the brand is not important)

In terms of specifications the umi 17 vs the umi17se is the reduction ratio

(500:1 vs 400:1) the payload is identical etc.
Is there a reason or a benefit of one over the other? I have seen this on other mounts as well.

[Nikolas]

Come on we have tech heads in here someone must know

[ChrisV]

Well I'll have a guess. Normally you'd associate a higher ratio with greater precision and higher torque on any drive from stepper motors. But their numbers don't seem to suggest a higher payload. Go figure ! It certainly makes the mount heavier

[joshman]

The 1:400/1:500 is the final drive ratio between the Strain Wave Gear output and the motor input, This ratio would also take into account the SWG reduction and any reduction in getting drive from the motor to the SWG.
If i were a betting man, i would say that they've either:


Changed where they source their SWG from, and have to change out of necessity, or
They've recalculated pay load limits and can get away with a smaller SWG unit to save some manufacturing costs.

[Nikolas]

Thanks but I still want to know

Which ratio is better 500 or 400?

[AlexN]

You'll probably find the answer is neither...

Typical knowledge would have you say that you'd get more torque and precision from higher reduction ratio, but when you're talking about the difference between 400:1 and 500:1, on a motor that's already moving in microsteps I'd say the tangible difference is negligable at best.

The lower reduction ratio mount will slew faster than the higher reduction ratio mount (by simple rule that if you're slowing things down, the motor has a max speed... so it will slew 20% faster at 400:1 than it does at 500:1.

The 'gold standard' ZWO AM5N runs a 100:1 ratio, if that's of any assistance?

Mounts like the RST135E, and the WarpAstron do not run such a reduction gear, and are direct drive via servo motors, so they are different in that respect... I'm not saying the Zwo is the best harmonic mount in the game, but if you look at proliferation, its kind of like the EQ6-R in the mid 2000's to early 2010's... Sure, the losmandy was a better mount, but the EQ6 did absolutely everything the average user needed for 1/5th the price, so they filled up majority of the market segment...

I guess with the UMi mount, you're looking at the underdogs because they are around half the price of the ZWO, hoping to find the 'EQ6R' of the harmonic mount era... What I'd say though, is the AM5 IS the EQ6R of the harmonic mount era... You've got Rainbow Astro, Warpastron and Pegasus in the higher end of the 'common' consumer market, You've got the middle runners with ZWO, iOptron, Sharpstar and Emcan Astro, then Proxisky/meowastro and a handful of other clones of them in the cheaper space...

Facts are:
Will it do what you want it to do without issue - most likely.
Will understanding the mount ratio differences make the mount better or worse - probably not.
Will you be sacrificing SOMETHING in order to get a harmonic drive mount with similar specs to the mid-range mounts at half the price... Yes.

I wouldn't obsess too much over which harmonic mount over another... Remember they are all made in China and the components are probably all made by the same OEM... Its really a case of 'pick your favorite colour and buy that one'...

[Nikolas]

Thanks Alan makes sense