[intel2you]

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.
Thanks in advance

[Al_The_Man]

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.

[intel2you]

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

[Al_The_Man]

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.

[txcncman]

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.

[johnsattuk]

How about -

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

[mike_Kilroy]

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

[intel2you]

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.
[ame=http://www.youtube.com/watch?v=rWQKoEB7tl0&feature=relmfu]LightBridge Meade Telescope balans test on RB 100 mount - YouTube[/ame]
[ame=http://www.youtube.com/watch?v=dAiYPMANUns&feature=relmfu]RB 100 amateur mount - testing - YouTube[/ame]
[ame=http://www.youtube.com/watch?v=CdUiJ-g_oEE&feature=relmfu]RB 100 amateur mount - YouTube[/ame]

[Al_The_Man]

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.

[intel2you]

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

[wildwestpat]

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

[intel2you]

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"

[johnsattuk]

How about -

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

Looks like you don't need continuous rotation, just 90 deg or so. If I were making it as a DIY project I would try use T5 toothed belt driving a flat pulley 220 ish dia (would need to work out actual dia from belt geometry) and fasten it to the pulley (to avoid it slipping) with a screw in the centre of your arc.

I would also look at a laser cut gear/pulley made from several 2mm cuttings fastened together. (2mm would cut cleanly and acurately).

As you are not doing continuous rotation you do not need a whole tooth solution eg: 10 tooth pinion/pulley driving 110 ish (70.5 teeth) pulley, this may enable you to fit into your design more easily.

A combined stepper motor and harmonic drive gearbox is neat and quite robust with zero backlash, it will have a 10/12mm dia. (depending on size used) shaft running on radial thrust bearings that you can mount the pinion/pully on to directly, . Would give a simple solution with minimum effort.

[wildwestpat]

I am rewriting this reply as there are some fundamental design points that you should be considering if the bigger head is intended to have greater magnification as well as light gathering.

1. The heavier the head the greater the need to ensure the head is mounted through its centres of gravity in all three planes. This goes a long way to eliminate any toppling effect as the head moves. This toppling force would cause errors in the bore sight to computer calibration so balancing the head is the best way forward.

2. The side saddle type of mount in your illustrations is less than ideal but could be made to work at the expense of beefing up the mount to accept the increased out of balance load variation. You could add an arm with a counter balance weights but this is going to get clumsy.

IMOH your way forward is to balance the moving head about the elevation pivot bearings such that the head has little or no tendency to tip under its own weight due to gravity. All the increase in weight means greater load on the support bearings and structure including the azimuth bearing. But with the head is statically balanced about both elevation and azimuth pivot centres there would be no extra errors introduced when the head is tracking. The use of the single sided mount makes this difficult to achieve - you could add counter balance weights to achieve the balance but IMOH providing elevation support on both sides of the scope would make for a much steadier viewing. Suggest you look at the design of large radio and optical scopes - they have supports on each side of the dish / reflector to avoid the changes in turning moments as the dish / head rotates.

Returning to the gear box the size of the teeth is very much a secondary issue provided the head is statically balanced about its axis of rotation (both elevation and azimuth) However the motor torque required will increase with the inertia of the mass to be shifted increases. There are formulae for working this out but it is complicated by the high gear ratio you need. I would use the existing motor having balanced the head.

If you opt for not balancing the head about its axis of rotation then you will have improve the rigidity of all the parts from the elevation bearing down to the ground support to cope with the changes in forces involved as well as increasing the motor torque and increase the torque the gearing will stand. It is likely that these forces will cause problems with scope aiming and thus negate the use of the computer drive as the droop would probably exceed the field of view. But the torque required will make this a difficult design as each step of the motor (I am assuming this is a simple stepper motor powering the axis) will try and induce resonances in the structure.

Thus I suggest you need to work on both the static balance and or the strength of the support for the elevation pivot/s before beefing up the gear teeth. Assuming this is a stepper motor drive then it is probably going to have enough grunt (torque) and if not it is simple to upgrade the motor and or driver. More torque than is required runs the risk of inducing more wobble in the field of view.

Hope this helps. Regards - Pat

[Al_The_Man]

Using a BLDC or AC servo will allow up to approx 6000 rpm max input rpm. So gearing is not a problem, for a similar application I have used a couple of Bayside Planetary Gearboxes, If the output style is the largest with a ratio up to 100:1 and the smaller input gearbox is 10:1 that is 1000:1 if needed driven by a NEMA 25 sized frame servo .
This makes for a very compact mechanism.
With a servo driven system the rate can be easily programmed.
Planetary G.B's are usually available cheap on ebay.
Al.

[intel2you]

Wow now u guys are getting me so lost in translation lol. The mount is done and yes it is balanced you can turn the 16" scope with one finger when it's on the mount only reason I say 100 pound is that when turn at high slew speed it needs to stop all the weight under it own enersha.
I tryed my hand twice at figering out the gearing 1st time it turned backward (ops hehe) time 2 gearing was wrong and didn't stop at the right place. I just made smooth round gears of stainless I got $500 in wasted try's stainless is not cheap in in 1 1/2 thick plate the pec was only at 2 arc min witch I think was good for something of this size at least the what the controller said. I just need the gear sizes in between motor shaft is the driver at a 1/4" and the shaft to be driven (output shaft the scope plate is fast to) is 1 7/8" and if that's to small I can make a bushing to make it bigger. Maybe I'm not asking my questions right my head gets foged full of sh.t thanks to my ADHD and sh.t don't come out right all the time. Long storie short is I just need to know the size to make the gears to get the 705:1 and still have some toque I can change any of the size I have to make it work. Thanks again

[Al_The_Man]

Gearing factors are a direct result of the ratio, if you commit to 705:1 to obtain a certain output this means that your input rpm is already defined and set in stone?
Al.

[wildwestpat]

Hi Interl2you

Lets take this one step at a time.

1. Your scope head is balanced so it stays where ever it is put.

2. You need to have the gearing down of the motor fixed at 705 turns of the motor to one 360 degree flip of the scope head.

3. Yes the motor must be capable of not only turning the head but also stopping it and holding it on station.

Is the answer to 1 and 2 yes?

The reduction ratio 705 : 1 can be arranged in several different ways. I would suggest that a worm wheel be placed on the shaft that supports the scope head. This will put the motor in charge of the position and go a very long way to stop the inertia having an effect. Ideal find would be a 180:1 worm reduction. The wheel being the output shaft and the worm the input. Find this part first and try and get a high reduction ratio. Note the shafts are at right angles to each other on a worm drive gearbox. You may strike lucky and get one with low backlash. (Backlash is slop in the input shaft which on reversing direction causes no motion of the output - worm is input and gear is out put).

At the expense of more weight a source of high reduction precision worm gearing is a dividing head would be a source of 90:1 worm and wheel built into and a nice mounting bracket. Both 90:1 and 60:1 are around just check how many turns for a complete revolution.

Thus if the found worm drive has a 90:1 reduction then the 47:12 reduction increases to compensate. That is 90:1 + 94:12 Put the put the pulley with 94 groves on the worm input shaft and the 12 groove on the motor shaft. Ask again if you find 60:1 as the other gearing will need to compensate.

Google for 'dividing head picture' and because you do not need the dividing plates - chuck you may find a bargain as all you need is the basic worm and wheel mounted in the nice cast iron angle bracket.

Hope this makes it a bit easier to get the picture. You have done well to get the head balanced. Normally the computer drive to the stepper motor would have a slow acceleration and a slow down to stop built in to make stopping easy. As you have doubled the weight the inertia will be at least four times as great but the use of a high raduction worm gear reduction will help stop the tendency for the inertia to cause an overshoot.

Keep asking if I am not making sense - regards - Pat

[intel2you]

I've been doing more reading I got to possible options one is a timing belt as some one said but what size would I need to hold it next is to cut some worm gears on the cnc and cut the gear teeth on the lathe I would need 705 teeth how would I figur out how big around to make it? These are just posable options thanks
Found the reason they use worm gears is that the only way the scope can move is if the motor turns as a worm will not turn and hold on less the motor turns it.

[intel2you]

Hi Interl2you

Lets take this one step at a time.

1. Your scope head is balanced so it stays where ever it is put.

2. You need to have the gearing down of the motor fixed at 705 turns of the motor to one 360 degree flip of the scope head.

3. Yes the motor must be capable of not only turning the head but also stopping it and holding it on station.

Is the answer to 1 and 2 yes?

The reduction ratio 705 : 1 can be arranged in several different ways. I would suggest that a worm wheel be placed on the shaft that supports the scope head. This will put the motor in charge of the position and go a very long way to stop the inertia having an effect. Ideal find would be a 180:1 worm reduction. The wheel being the output shaft and the worm the input. Find this part first and try and get a high reduction ratio. Note the shafts are at right angles to each other on a worm drive gearbox. You may strike lucky and get one with low backlash. (Backlash is slop in the input shaft which on reversing direction causes no motion of the output - worm is input and gear is out put).

At the expense of more weight a source of high reduction precision worm gearing is a dividing head would be a source of 90:1 worm and wheel built into and a nice mounting bracket. Both 90:1 and 60:1 are around just check how many turns for a complete revolution.

Thus if the found worm drive has a 90:1 reduction then the 47:12 reduction increases to compensate. That is 90:1 + 94:12 Put the put the pulley with 94 groves on the worm input shaft and the 12 groove on the motor shaft. Ask again if you find 60:1 as the other gearing will need to compensate.

Google for 'dividing head picture' and because you do not need the dividing plates - chuck you may find a bargain as all you need is the basic worm and wheel mounted in the nice cast iron angle bracket.

Hope this makes it a bit easier to get the picture. You have done well to get the head balanced. Normally the computer drive to the stepper motor would have a slow acceleration and a slow down to stop built in to make stopping easy. As you have doubled the weight the inertia will be at least four times as great but the use of a high raduction worm gear reduction will help stop the tendency for the inertia to cause an overshoot.

Keep asking if I am not making sense - regards - Pat

1 yes it is weighted 1.5 pound to the back to make up for eyepieces
2 yes 705:1 I would assume they mean to one turn of the motor