# Thread: How to get a 705:1 gear ratio

1. ## How to get a 705:1 gear ratio

I am be posting in wrong place if so please let me know where to put this and I'll post it in the right place.
I need to end with a 705:1 gear ratio and cant seem to find how to end up with it? My plan is to run a smooth round wheel (as my large gear) running direct for the 1/4" motor shaft the large gear will then run put up against the last shaft witch will run the device? If needed I can post a quick diagram if ya don't understand what I mean put the end result need to be a 705:1 ratio.

2. It almost sounds as though you want to achieve the reduction with just two reduction elements directly connected?
You will actually be gearing up not down 1:705.
You would end up with large devices, e.g. a 705" dia and a 1" dia wheels and your torque will be reduced by the ratio!!
Why not run the final shaft direct at a fixed or controlled rpm?
Al.

3. I can run more gears if need be but as few a I can but it has to be a 705:1 one I have no choice in this or it will not Aline right and I need as much torque as possible as it will lifting a 100 pound. when I get home I'll try to get some pics of what I'm trying to do. Thanks

4. If your motor is on the large wheel side, as I mentioned your torque will be reduced by the ratio 1:705 which will be considerable however you gear it.
Al.

5. Put a 70.5" gear on your 1/4" shaft. Then have the 70.5" gear drive a 1" gear. Have the 1" gear coupled to another 70.5" gear. Have that gear drive another 1" gear. Have that 1" gear coupled to another 70.5" gear. Have that 70.5" gear drive another 1" gear. Have that 1" gear coupled to another 70.5" gear. Have that 70.5" gear drive another 1" gear.

...Do this until you have 10 gear sets with the final 1" gear coupled to your final drive shaft.

Or, like Al said, you can have one 705" gear on your motor shaft and one 1" gear on your final drive shaft. 705" = 58'-9". Are you sure your shop is large enough to handle it?

Also divide your motor horsepower/torque by 705 to get the final drive torque (not accounting for friction). Also multiply motor RPM by 705. (705 times 0 RPM = 0 RPM when the motor cannot overcome the torque needed to start.)

Please post pictures of the result.

6. ## 705:1 gearing

100:1 harmonic gearbox with a 20 tooth pinion driving a 141 tooth gear.

7. how about buying a 705:1 gearbox? we sell em so I am sure many others do too.

8. 180*47/12=705

(180 teeth on worm gear, 47 on worm and 12 on motor shaft)=this is the motor and controler doner gear specs its a skywatcher eq6 mount.
these are the gears in this this thing stock none are biger then then 5" these are done in teeth but dont need to be i hope its ok to post links to videos but this is what im trying to build.

9. Well your video's appear to be the opposite of you initial description which was described as 1:705.
You apparently need 705:1.
Which is a different story!.
I am still unsure how or why you came up with this particular ratio, if the final output rate is the only requirement, then the ratio is a design criteria, IOW what is the significance of the 705 figure?
There is a previous post here by Ceefna of a terrestrial camera operated mechanism which appears akin to what you want, no?
Al.

10. Lol ya I need 705:1 this Is what the controller is programmed for witch I can not change I'm not good at describing stuff but yes that's what I need. I was told even though it's 705 gearing I could change the gears around to get the 705:1 and take some stress off the motors is by going strait off the 1/4 motor shaft and not using the intermediate gears is that true? And I think I seen that post he did not stick with the 705:1 gearing as he was going to use a computer to run it and not the stock controller. As the guy did in his video hes got a 100 pound hanging on there an I'm trying to do the same. I asked him we talked a little but hasn't been back on sence and I'm stuck on this gearing problem and I guess I suck at gearing because I can't figer out what I need for the sizes. I will also need to upgrade my 1.8° steppers to what he has. But I'm now at a standstill an he not answering. Thanks

11. This ratio appears to be much in demand by star gazers here is one link

EQ6 belt drive modification - Page 2 - Stargazers Lounge

They use a high ratio worm drive with a conventional input gear or toothed belt. the ratios are 47:12 + 180:1 Ratio is 704.9 recurring. You might also use a third stage reduction to split the 1:180 down in to sizes to suit your construction BUT a worm wheel drive is good as it protects against back driving to a very large extent. I think smoothness of operation and backlash are also issues so toothed belts and antibacklash worm wheel might be requirements if this is to computer track distant objects. High viscosity grease with large plain bearings might help damp the beast!

But the astro site is where the action is on this one.

Hope this helps. Regards - Pat

12. Yep I have read them all on the astro sites the mounts they are working on are the stock mounts that only hold up to 48 pound and that is pushing there upper weight limit and I will be hanging a 100+ pound on mine the same setup as the videos to the Tee a what u fail to see there is the timing belt only get rid of one gear there are 4 in it and a single belt will not hold that weight. I need a gear setup like the video has. I've ask on a half dozen astro site and all I got was wow you need a gear with this many teeth but I can't make teeth I can cut the wheels on the cnc then turn them smooth in the lathe. I tryed one set I made in it with the small motors and just a 4"scope straped fast to it it turned good but not where it was apost to go my gearing was wrong. No where close "lol"

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