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 Affordable low backlash worm gearing? 
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Post Re: Affordable low backlash worm gearing?
Well i will put my bit in as i have always done multipass as A) a way of testing your system and B) Its essential in modern stop frame animation for rig removal .
I have done laser tests too but i find these rather misleading . Its hard to read a tiny division the lights to bright and sometimes dispersed . Secondly if the thing isn't mounted well you may get a bit of movement or even movement from other areas such as the floor you may be standing on at the time .
As Gerald says just run your proposed range of shots and see if you rig can cope with it. You may be pleasantly surprised or sad depending on the results :( I had this problem with my robot arm early tests indicated it would never be able to mulipass therefore it was a no goer and a considerable waste of time . Sciencelookers never did a postmortem on his robot arm so i always wonder how that one went
I cant remember what ratio your gearbox is ?I had a little look back but nothing jumped out i assume its around the 50 to 1 mark. I can easily achieve this with just a couple of timing pulleys and belts with no noticeable backlash with or without load. So what i am thinking is you are working very hard to achieve something that is all ready possible a lot easier and cheaper with pulleys and prob offers better results. Soz just a opinion !
D1


Sat Jun 25, 2016 4:43 am
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Post Re: Affordable low backlash worm gearing?
@James, @Gerald,
Thank you for your kind words, thorough feedback and advice!

Gerald, I'm not very familiar with the black screen testing. I mean, I learned about it here, on timescapes, I know that in principle it's all about shooting two identical scenes and superimposing the frames while using a "difference" blending mode, to detect any differences between the two frames. But I'm not sure if we're talking about film or about still shots. Since I'm focused more on time-lapse than on real-time video, I will do a still frames repeatability test, with both an 11-16mm Tokina (having some objects very up-front) and a 70-700mm Canon (these are my most extreme glasses).

Just a note on video: I remember a very productive conversation about the Chinese HDs being sub-par in terms of working vibrations, when compared to the real McCoy. My gearbox is definitely not as smooth as an original HD, because it's not using an elastic ball bearing, but a steel-bronze interface. However, right now, the biggest source of vibrations in the rig isn't the gearbox, but the closed-loop stepper motor, when homing in to a position (some positional error also comes from minute amounts of servo error in there, at the input - hence the sub-arc-minute variations). This (besides me not being familiar vith real-time video) is the main reason for not going to do a black-screen test with real-time video.

So, in line with your so very common sense approach, I will devise a rig to control the camera on only one rotational axis (should this be PAN or TILT? My bet would be on PAN, because TILTing preloads the system and this is not desired). This is both because testing one variable at a time makes so much sense, AND because for now we only have this one gearbox prototype ;). Then I'll do a couple of still frame sequences, to test the repeatability, and post the results back here. This will happen no sooner than the middle of July, since in 2 days I'm going away on a much awaited vacation ;)

Thank you again for bearing with me after all this time,
Eros

P.S. Here's your truly (in red), today in the Fagaras Mountains (south of Transylvania), with a coleague, setting up a simple slider for a cloudy day, simple time-lapse:

Image


Sat Jun 25, 2016 10:51 am
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Post Re: Affordable low backlash worm gearing?
@DISPLACEMENT
Sorry, just now did I see your reply too. Yes, the gearbox is a 1:50, in itself, and the complete unit will be a 1:100 or 1:200 (as I plan on using a pair of timing pulleys for biffing up the stepper 2x or 4x - what for enabling me to use lighter motors)

Absolutely right: all the dry testing in the world won't help if real life conditions prove your efforts futile. Sure, lasers do help you at first (at least to know you're in the ball park), but real scenario testing may very well wake you to the realisation that for instance you have a spot-on gearbox but that the rest of the robotic arm is so flexible it itself induces more error than the gearbox's backlash...

I did try the old timing pulleys and belts trick, initially. A very ambitious custom pulley, 2-stage 1:100

Image

BIG FAIL. For a couple of reasons:
1. Belts too slim (I went with 6mm, should've tried 12mm at least)
2. Too flimsy setup (5mm aluminum flats)
All would have been fixable (to double the belt widths, to biffy up the jig) but what I did notice worth of interest was that, while belts themselves are indeed pretty strong, THE rubber TEETH themselves are always soft enough to yield to shearing forces way below the tensile strengths specified for the belts. In other words, it's futile to have a strong belt, when the teeth themselves act like gummy bears. Sure, when you have 50 belt teeth engaged with the timing pulley, you'd be hard press to find any flex, but when you're using a 20 toothed timing pulley, of which the belt only engages, say, 8 teeth, the effect is immediately evident.

To me, the only two systems in the world that have mathematically linear power reduction AND real-world zero backlash are the smooth-contact, zero-pitch, infinite-tooth ones used in astronomy:
- biffy, chunky, smooth surface, case-hardened wheels with different diameters, contacting each-other under constant pressure (absolute precision, pretty low load carying capacity due to slippage under biger loads)
- smooth-surface, case-cardened wheels with smooth steel belts (higher load carying capacity due to much bigger contact area, but prone to belt elongation)

Obviously, the above are only applicable in high-budget, big-weight applications, not here, but I thought I'd bring them into discussion simply because they are the extreme of the world of gear-meshing ;)

Eros


Sat Jun 25, 2016 11:30 am
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Post Re: Affordable low backlash worm gearing?
Eros,

You don't have to use rubber belts, you could use anti backlash PU belts with steel reinforcement such as Synchroflex Generation 3 in AT5 teeth, for instance.


I am sure you have explored these, but here is the description anyway:

The Synchroflex GEN III range of belts consists of only two components, a wear resistant Contilan carcass as well as high grade endless steel wire tension members in 'S' & 'Z' pairs. The strong bond between the two results in a Synchroflex belt with high tooth load capacity combined with low elastic elongation, making them unsurpassed for quality and accuracy.

The Synchroflex process produces close tolerance timing belts to ensure optimum mesh in all power ranges.

SYNCHROFLEX belts comply with DIN 7721, having proved themselves in operation for more than 30 years. Synchroflex timing belts are manufactured in moulds giving pre-defined lengths up to approx. 4780mm long.

----------------------------------------------------------------------

As D1 mentions, it's not too difficult to achieve a 2 stage reduction of 50:1, although with a tooth profile of 5mm, the pulleys would be rather large, maybe you could aim for 25:1 instead?. There is also AT3 in PU which would be suitable with smaller pulleys. Lately I have been very happy with rubber HTD3 belts for smaller pulleys, as the rounded tooth profile has better contact and less drag, allowing higher torque with less tension. Still your gearbox sounds like fun, but maybe you are complicating your life too much?

If you have a good stepper driver, you can get away with less reduction.

Edward


Sat Jun 25, 2016 2:07 pm
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Post Re: Affordable low backlash worm gearing?
Hi Eros

"I know that in principle it's all about shooting two identical scenes and superimposing the frames while using a "difference" blending mode, to detect any differences between the two frames. But I'm not sure if we're talking about film or about still shots."

Re film and stills - the same testing approach applies to each, but realtime is much more likely to show issues than stop frame. In stop frame the rig has a chance to settle before the exposure. During constant motion there may be instabilities introduced by the structure of the rig - though this applies mainly to transverse or linear motion, rather than pan and tilt. Pan and tilt will normally be less prone to vibration and other issues, unless the camera is unusually large or heavy.

It may also depend on the control system, since in real time the axes may not be so accurately coordinated. For instance using an Arduino controller with DF - in realtime movements the axes are only approximating the move - so if you compared the stop frame recording with the realtime move - they will likely be different. Also of course the realtime move will have motion blur - which is why I mentioned using a small shutter angle.

Another issue not mentioned is camera sync. In stop frame sync is guaranteed, but in realtime, while the passes may be the same, they could be captured up to half a frame offset if the motion control playback is not synchronised with the camera shutter. That is an important difference between Mantis and DF, since DF has no option to lock the move to the camera in realtime.

This is also why testing should include direction changes and a variety of speeds. In a slow regular movement it is easy to hide an offset that might only reveal itself when speed or direction changes.

As for using difference matt (black frame) vs split screen. I prefer split screen because it renders faster and also enables you to see more immediately if one image is advanced or retarded relative to the other. Difference matt can also have more difficulty if there is a lighting change between passes... but really it's up to you.


Sat Jun 25, 2016 8:22 pm
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Post Re: Affordable low backlash worm gearing?
PS - re the "big fail" example. In addition to the comments by Edward I would add that the structure is a problem. The size and length of the camera support arms will increase any inclination for the belt drive to vibrate. For this reason a pan tilt head should be as compact and well balanced as is practical. A more extreme example is a boom arm, which must be rigid and have a strong gear drive without flex.

As you have effectively demonstrated by applying a friction load to your gearbox, all gear drives have "lost motion" which is equivalent to adding a spring to the system. If there is too much, then oscillations can arise. Luckily with a pan tilt head this is normally not such a problem, since the inertia of a small and balanced load is relatively low...

PS - beautiful location in Transylvania! :)


Sat Jun 25, 2016 8:42 pm
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Post Re: Affordable low backlash worm gearing?
@Edward: I didn't use rubber belts. I only called them "rubber" as a metaphore for the apparently weak results I've gotten with them. In fact, I used the best ones I could find on SDP-SI: TruMotion® Timing Belts (polymer compound with fiberglass tension member - http://shop.sdp-si.com/catalog/product/?id=A26Z16M200095). Also, another reason for failing might have been my ambition to achieve a compact dual-stage 1:100. This means two 1:10 via timing belts. As you can see, the big pulleys ended up too big anyway to be practical, even at a 2mm pitch.

In hind sight, to have a decently robust timing belt reduction, you'd need to use bigger everything:
- wider belts (you can easily end-up with 2 inch thick dual stages - huge)
- bigger pitch, like 5mm (but this makes the pulleys huge, even for modest reduction ratios. A 1:4, for instace, means a measly minimum of 12:48 teeth, or 19mm:76mm diameters; rather, a 18:72 teeth, or 28.5:114mm diameter pulleys. Absolutely impractical)

This would scale everything up to cumbersome volumes and weights, utterly inappropriate for anything backpack portable. Adding to this the multiplication of the first stages' backlash through the second stage, I put the whole idea of exclussively-belt-based reduction to rest, for now...

3mm belts sound more decent and doable, even if more teeth would be required on the pulleys, which would again result in big, custom made and expensive pulleys - but my dual stage experiments led me to believe, for now, that timing belts are good for precision under small loads, not for strength. As you might have read in my replies, I will still definitely continue to use timing belts, but only for lightweight applications, like a modest motor up-gearing at the input of a gearbox.
Eros


Sun Jun 26, 2016 2:43 am
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Post Re: Affordable low backlash worm gearing?
Hi Eros.

It's likely the fibreglass tension members are not as rigid as steel? I think a dual stage pan or tilt can still work and that 100:1 is unnecessary.

I have personally used 37:1 via a worm gear and found the resolution quite adequate for general use - though not so ideal for telephoto or extreme macro. But also as mentioned it depends on the inertia of the load. Working with DSLR's actually requires very little torque in a well designed frame. ie. where it is balanced.

But as you say, a small belt pitch is necessary to avoid overly large custom pulleys..


Sun Jun 26, 2016 3:11 am
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Post Re: Affordable low backlash worm gearing?
As Gerald says, 100:1 is unnecessary.

I use At3 steel reinforced belt and it's much much better than MXL. Unfortunately, the pulleys would still be quite large.


Edward


Sun Jun 26, 2016 3:51 am
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Post Re: Affordable low backlash worm gearing?
@Gerald: Your thorough replies make me feel - again - a complete noob here :) Thank you so much!

These last two replies made me realise and re-state two essential tings:

1. That I'm definitely too far away from the technical/financial resources needed to advance my project, right now, from still frame-by-frame, to real-time video. So, for now, black-screen, instead of split screen, since synching will not pose a problem ;). I'll be more than happy, once we're ready for it, to manufacture a couple of extra gearboxes for some of you guys (@James, you'll be the first!) for testing on your own real-time rigs. But for now, I stand limited to frame-by-frame.

2. That my current omnihead design, while still much more compact and weight-centered, may still be too large to be very rigid. It came out like that mainly to accomodate the biggest DSLR on the market, with a 200mm lens on it, optically centered on the intersection of the three movement axis (you can see a smaller, Canon 5D, with an 80mm on it, for reference, below).

Image

So my next focus, after the black screen tests, will be to try and refine my current omni-head design to make it more compact and thus more rigid.

About timing pulleys: My main focus, from the get-go, was to achieve a wide spectrum of optical capabilities: from ultra-wide lenses (requiring that nothing on the omnihead protrudes more than 30-40mm beyond the focal distance, lest it should be visible in the frame) to medium tele lenses (around 200mm, where you need quite a lot of movement resolution and rigidity). So my requirements / limitations were, from the very beginning, to have something very compact (for ultra-wide) and very resolution-capable (for the tele). That's why I shot to achieve that unrealistic 1:100 (and still am, via the gearbox). But, again, it's very un-realistic via timing belts, not as much because of the tension member elasticity, as because of the micro-yielding of the teeth themselves (and un-realistic because of the bulkness of the required pulleys which, by the way, are non-standard, hence expensive as hell - some shops in the US asked as much as 900$ for a single 130 teeth GT2 pulley... ridiculous)

About balancing: it's you guys, here, who turned me around long ago, from the ambition to build a strong, unbalanced rig, to the practicality of building a well balanced one, so thank you for that! I'm sold on that one! ;)

Eros


Sun Jun 26, 2016 3:58 am
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Post Re: Affordable low backlash worm gearing?
About MXL belts: can't even remember why the hell I went with those in the first place... Maybe just because, being cheaper, they were the preferred choice in the 3d-printer building community where I drew my first experience with stepper motor control... Nowadays I'm also a fan of GTs...


Sun Jun 26, 2016 4:12 am
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Post Re: Affordable low backlash worm gearing?
Hi Eros. From a balance point of view this is better, though a small point remains with the roll motor which will make it top heavy. If it can be located level with the rotation axis it will be better - though it will need to point forward not up - so the drive may need revision.

Note that for driving the roll axis, a long belt wrapped around the ring is entirely satisfactory, as the gearing is integral with the motor and not much gear reduction required there anyway.

Finally if you can reduce the overall width by using a smaller ring diameter, it will also reduce the inertia experienced by the pan axis. If you assume that the camera body is always mounted behind the ring, then this is entirely possible.


Sun Jun 26, 2016 4:19 am
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Post Re: Affordable low backlash worm gearing?
(..) The size and length of the camera support arms (..)

hi all
some interesting facts about stiffness and strength I didn't know..

2 aluminium bars with rubber bands:
https://www.youtube.com/watch?v=MtxA20Q-Uss#t=1m23

and the formula for stiffness:
https://www.youtube.com/watch?v=a_E-tYRxBkU#t=13m10


Sun Jun 26, 2016 4:58 am
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Post Re: Affordable low backlash worm gearing?
Hey, Gerald,
Yes, a symmetrically placed motor, positioned on the horisontal axis, would be better, indeed - but it would entail the extension of one of the gymbal horisontal pivots. Not a biggy, anyway.
About the orientation of the motor: my initial plan was the same as yours: to have a belt around the whole inner ring of the bearing. But I wasn't sure if I could/should machine teeth into that extra surface, to engage with the belt, or if any rough surface would do, given the big contact surface...
The current approach uses a different orientation of the motor, involving the shaft transmitting power via friction exclussively to the side of the inner ring. VERY doubtful it would work reliably, VERY tempted to go back to the initial approach (the one suggested by you too) and to test it without any teeth on the belt-ring surface. Thank you for reminding me of this.
Now, after today's delightful feedback from you guys, I am also totally re-considering the size of the gymbal bearing - now that I already made one, I am confident I can repeat the experience any time, so I'll re-do all the math, to see if I can make the whole gymbal unit sensibly smaller.
Eros


Sun Jun 26, 2016 5:02 am
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Post Re: Affordable low backlash worm gearing?
I just watched Mr. Dan Gelbart's tutorials some months ago... Truly inspiring, for noobs / non formally educated in these matters, like me, coming from a guy who could have sitten on his big pile of money instead of sharing from passion and knowledge... Thanks for bringing those links up!
Eros


Sun Jun 26, 2016 5:53 am
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Post Re: Affordable low backlash worm gearing?
DISPLACEMENT 1 wrote:
Its hard to read a tiny division the lights to bright and sometimes dispersed . Secondly if the thing isn't mounted well you may get a bit of movement or even movement from other areas such as the floor you may be standing on at the time.


@D1: Forgot to mention:
- For the laser testing, I looked for (and used) a laser with a pattern dispersing crystal (as can be seen in my video, where you can see an actual dots pattern showing up, instead of a single dot). This presented itself to me as the single most cost-effective ($12) way of getting a laser spot that is small enough at over 10m distance, since all small divergence lasers are neither that "small divergence" (just marketing, really) nor that affordable, at over $600-700. With this patterning crystal, all the resulted dots are, individually, much smaller than the original single dot - hence less bright and more precise.
- For avoiding any floor-related issues, we had the rig set up in a different room, remotely controlled via WIFI


Sun Jun 26, 2016 6:42 am
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Post Re: Affordable low backlash worm gearing?
Eros - yes you could get away with a friction surface on the ring for the belt due to the large diameter - or very simple machining of "teeth".

Friction drive on motor shaft is a non-starter - it will creep very soon!

The lessons from Dan Gelbart are interesting. But do consider using a tube structure for the arms. Stiffness is proportional to depth, so a hollow section will be much stiffer than a solid of the same weight.

Also from Dan - the bearings on either end of the gimbal don't need to be so substantial due to distance between them - but the ones you use on the pan base are very critical! Perhaps large diameter cross roller or 4 point contact bearing (expensive. :( ) or if you can allow the extra height - a pair of normal bearings with some pre-load.

The wider and higher the whole structure, the more critical is the base pan support bearing... but even if you make it stiff enough, a high center of gravity is still an issue - so keep it all as compact as possible... :)


Sun Jun 26, 2016 6:55 am
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Post Re: Affordable low backlash worm gearing?
Hey, Gerald,
Now, that you mention it, this alternative does sound much more reliable than my planned one and, should I determine that we can do with a smaller bearing, it will most likely include this feature (the extra rim for accepting a slim timing belt).
My initial approach was with hollow rectangular tubes (2-3mm walls). People tell me openbuilds profiles might be much stronger (but heavier too). I wonder which solution would provide the best rigidity/mass ratio...
About the panning bearings: My plan is to use two preloaded tapered bearings set apart by around 30-40mm, and perhaps an axial bearing to help secure some of the weight of the rig that might slip, in time, downwards. Would this axial bearing be overkill?
The height of the structure will most likely depend on the diameter of the big ROLL bearing. As I write this, I see that I could also reduce height by offsetting the PAN motor to the side, and driving a timing belt from it to the pivoting axis. The forces involved in panning are so low, that this might actually work, and save a good 6-7cm of height...
Eros


Sun Jun 26, 2016 8:25 am
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Post Re: Affordable low backlash worm gearing?
Hi Eros

Extrusions are quite heavy, their main advantage is ease of fitting bolts etc. Tube will definitely give the best weight strength ratio.

For the pan base you won't need a thrust bearing - tapered rollers can handle the thrust load easily...

PS - You probably realise already, but the base tube needs to be stronger than the two sides, since it will experience twisting forces. Maybe some ribs inside can help or use a slightly larger section.


Sun Jun 26, 2016 3:39 pm
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Post Re: Affordable low backlash worm gearing?
Just a few weeks ago I had asked Gerald about whether certain extrusions would be strong enough for a short crane arm. Since then, I have tried to do something a bit less artistic and more engineering-like. One exercise was to compare the weight per unit length of various aluminum extrusions. Because I live in the US, I work with antiquated measuring units. T-slot extrusions similar to makerslide are available here, but they are measured in inches and feet. I weighed some of the 1030 profile T-slot extrusion used in Dynamic Perception's stage zero dolly, then compared it to rectangular and square aluminum tubes of various sizes and wall thicknesses. I was surprised to see how light the T-slot extrusions are compared to the others, although the square or rectangular tubes will be stronger. Just for reference, here is the list I compiled. Weight is per foot of extrusion. At far left is the size of the extrusion cross section, in the middle, its wall thickness and to the right, after the "=" sign is the weight in pounds per foot of extrusion. The only rectangular extrusion lighter than the T-slot one is the 1 by 3 inch rectangular tube with 1/8 wall thickness. Some of the larger extrusions I was thinking about using are much heavier. Those of you living in the real world can have fun converting this stuff to metric, or preferably post your own list with extrusions available everywhere else.

1030 T-slot extrusion = 1.33 (pounds per foot)

1x3 1/8 wall = 1.11
2x3 1/8 = 1.3966
2x4 1/8 = 1.6733
2x4 3/16 = 2.55
2x4 1/4 = 3.3
2x5 1/4 = 3.8219
2x6 1/4 = 4.48
3x6 1/4 = 4.99
4x6 1/4 = 5.586
4x8 1/4 = 6.72
6x8 3/8 = 11.675

Square tubes
8 inch 1/4 wall 9.09 pounds
6 1/4 = 6.745
6 3/8 = 5.1337
5 1/4 = 5.58
4 1/8 = 2.28
4 3/16 = 3.354
4 1/4 = 4.47
4 3/8 = 6.378
4 1/2 = 8.23


Mon Jun 27, 2016 8:20 am
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Post Re: Affordable low backlash worm gearing?
Hi SL

It's a bit like comparing apples and oranges, since you are comparing square tube to rectangular extrusion and only the larger sizes of tube. Wall thickness is also relevant.

In fact the strongest would be thin tube with internal ribs - but not really available off the shelf... you can also find online calculators that will tell you the exact bending rate of tube in different materials in various thicknesses. But it also depends on whether you are concerned about twisting forces vs bending. It can get fairly complex and sometimes testing is required. I often use 3mm wall (<1/8th) but you can use even lighter tube for a small pan tilt head..

Cheers G


Tue Jun 28, 2016 1:19 am
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Post Re: Affordable low backlash worm gearing?
Hey, guys,
It's been a long while - sorry for the slow updates.

I took it upon myself to start relying more on other's wisdom, so I found the formulas for calculating the torsional rigidity for various readily-available profiles (round bar, round tube, square and rectangular tube), both in aircraft-grade aluminium and in steel.
The parameters for this "experiment" are the piece's length (I chose 500mm) and the applied torque (100Nm).
The result is a Google Sheet with the results in angles in the first page and the possibility to change the length and torque in the second sheet.
I hope you enjoy and find this of some help sometime.
Here-s the link: https://docs.google.com/spreadsheets/d/1WDv2LhlTuL8n0sL_lNhaDqnJT1jIBrhPQai30LqBMpk/edit?usp=sharing

That's it for now - take care,
Eros
P.S. Since the sheet is editable, it goes without saying that leaving it in good working condition would benefit everybody interested in these numbers. I do have a backup, just in case, though ;)


Tue Feb 28, 2017 11:57 am
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Post Re: Affordable low backlash worm gearing?
Oh, one more small update: I don't have the easy access to a Solidworks-licensed computer anymore, so I saw myself forced to do something I dreaded: to turn to Fusion 360 for the modelling.
I really miss SW, but Fusion 360 does help, for now. Here's a screenshot of the current rebuild-sketch I'm working on (you will notice the stronger horizontal member with lighter vertical ones).
As a side-note, Fusion 360 tells me that what you see there (gymbal bearing, gearboxes, motors, frame) weigh in at around 6.5Kg. Quite a back-breaker for my taste, but that'll have to do for now...

Image


Tue Feb 28, 2017 12:32 pm
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Post Re: Affordable low backlash worm gearing?
Yes Eros. Saving weight on the frame makes less difference when the gears and motors are so heavy.. Don't use big motors unless you really need to. :(

If the camera load is balanced then tilt can have a smaller motor than pan. Normally pan should be the fastest and the most rigid axis.

My suggestion is try and keep it compact - with less height and width it will be more rigid... I mean think of it like a weight on the end of a stick.

The roll axis also creates some problems - if you can live without that it will be less of a headache...?


Mon Mar 06, 2017 4:26 am
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Post Re: Affordable low backlash worm gearing?
Hey, Gerald,
As always, I'm so grateful to be part of such a nice group and to receive such thoughtful feedback!

About the weight: couldn't agree more!
I'm painfully aware that balancing a bear on top of a straw is never a good idea ;)
The motors are this heavy just because the gearbox has a rather high starting friction - because of the bronze-steel interface used instead of regular rolling element bearing inside. Still trying to figure out a way to reduce this. As of right now, gearbox + motor = more than 1.5 Kg (3 pounds), which aches my back just thinking about it. Maybe I'm overdoing it...

As for the roll bearing: I initially thought the whole camera MUST fit inside the roll bearing - hence its very large diameter. In the meanwhile, talking with some local guys, I found out what I should've known years ago: that the nodal point is always outside the camera, into or beyond the lens body - which allows me to squeeze just the lens inside the bearing, not the whole camera.

So, as proud as I am for having built such a large diameter and nice bearing myself, I think a better idea would be to go with smaller diameter bearings (nowadays 300$ can bring you a nice pair of thin section ball bearings from China). This would allow for a much more compact mechanism, while leaving space for any follow focus rings actuation - see the image below, for comparison...
Eros

Image


Mon Mar 06, 2017 7:24 am
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Post Re: Affordable low backlash worm gearing?
Hi Eros.

The design looks quite good. If it is still with Fusion you are very patient. That program drives me crazy sometimes...

Yes the lens node is typically inside the lens. Though I think the need for making the camera nodal is not so important. So long as it is centered on the pan and tilt it's ok...

I arranged my roll head so the lens goes through the ring as far as possible, leaving space at the front for focus control. I also have horizontal sliding mounts on the side of the ring, so it can be moved forward to balance the camera. Otherwise I would need a strong tilt motor to prevent it dumping.

It is also worth considering allowing the roll to be swapped with a lighter weight U plate - for times you don't need roll... This could allow faster moves and also more clearance for skimming close to the set...


Mon Mar 06, 2017 3:48 pm
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