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 I made a new toy today 
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Post Re: I made a new toy today
that is ROCKING!


Sun Oct 19, 2008 4:09 pm
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Post Re: I made a new toy today
Good idea Thomas. I'll be very interested to see how the test footage turns out! If those DS motors are too lightweight you could look into the LXD motors... They run about $200 for a set. I have the part numbers if you need em.


Sun Oct 19, 2008 4:56 pm
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Post Re: I made a new toy today
Awesome! I'm working on a pvc dolly right now. I wish I had known about those DS motor kits before I started, that would have been way easier than hacking apart ds2000 mounts.

Image

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Sun Oct 19, 2008 6:28 pm
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Post Re: I made a new toy today
very cool. once perfected, you guys should think about doing these with metal.

i like the idea of the dolly car being self-propelled. it makes the dolly moves endlessly scalable, plus can eliminate wires running to a moving car on multi-axis rigs.

keep the pics and vids coming. :D


Sun Oct 19, 2008 9:37 pm
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Post Re: I made a new toy today
i'm just wary of using PVC/wood dollies from my motion-picture experience. they generally tend to be a little rickety. my friend chris built a pretty decent one using very wide-diameter PVC - "3 or "4 - but generally speaking, for long-term projects, once the experimenting is done, i would recommend aluminum or some kind of metal. that's just my opinion, though.

what i am looking at these days is low-profile aluminum "rectangular tubing." maybe around "3x"8, to use essentially as a monorail, raised and leveled with a tripod on each end. the trick with a monorail design is making the car's wheels fit snugly. it would be easy to power a monorail car with a simple winch dragging it down the rail, but i am not sure exactly how you could make the car "self propelling" on such a smooth monorail surface. maybe running some fine gear teeth down one side of the monorail?


Mon Oct 20, 2008 12:37 pm
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Post Re: I made a new toy today
I haven't gotten my dolly to run yet, I can't seem to get a motor working properly. I've tried two so far and they will both run for about 2 seconds and then stop, giving me a "motor fault" message on the hand paddle. I'm guessing at this point the problem could be due to my use of a 4 foot cat5 network cable to connect the motor to the circuit board. I don't know much about electronics but I'm hoping the problem is just that the cable is too long. As soon as I get around to shortening it we'll see what happens.

Oh, you can't really tell from the picture but there is a metal strap on top of the drive wheel connecting to another one on the other side. It's kind of a pain to set up but I can tighten the two to put pressure on the pvc track.

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Mon Oct 20, 2008 4:37 pm
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Post Re: I made a new toy today
tom wrote:
maybe running some fine gear teeth down one side of the monorail?


Prepaired to be shocked... I looked into this (as I was convinced that it would be a 'simple solution') and was quoted over $2000 for a 12 foot linear rack gear! Maybe there is a better source... Here is the company that quoted that (they have beautiful parts but frankly the guy I talked to was condescending and an ass) : http://www.schlenkent.com

Now granger has low tooth count (7 per inch) 4 foot sections (with a 1/4" bore pinon to match): http://www.grainger.com/Grainger/items/1L887 for around $65 but I wonder if this would be accurate enough for such small movements...


Mon Oct 20, 2008 5:21 pm
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Post Re: I made a new toy today
tmophoto wrote:
what speeds are you trying to run the motors at? same thing happened to me when i bumped up the ratio past 1.0 i think. I know it wouldnt move the motors for more than 2 seconds at 5.0 and 3.0

switch the paddle to max speed or drop the ratio down below 1

also mine does not like it when both motors are visible to the paddle on powerup, i have to have both plugged in when i power it on and just unplug a motor right after that. I will need to figure out some kind of plug to keep in there all the time or convert the paddle to plug directly into the motor.

t


It seems to happen at any speed or ratio setting. I've regularly run ratios up to 5x without problems on my dedicated panning mount (on the 8x speed setting). Even when I set the speed to 8x, the motor will still run it's 2 seconds at max speed and then stop. Then it goes into the testing motors screen, will cycle each motor for a second or two and then say motor fault. The ALT motor is not affected at all, in fact I've run it by itself for my zoom setup with the wires cut for the AZ motor, and it will still work just fine whether or not the AZ motor is plugged in. I know for a fact the new motor I have in there works, because I tested it before I ripped it out. I think either my circuit board is somehow faulty, or the length of the cord is causing it.

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Mon Oct 20, 2008 6:16 pm
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Post Re: I made a new toy today
milapse wrote:
tom wrote:
maybe running some fine gear teeth down one side of the monorail?


Prepaired to be shocked... I looked into this (as I was convinced that it would be a 'simple solution') and was quoted over $2000 for a 12 foot linear rack gear! Maybe there is a better source... Here is the company that quoted that (they have beautiful parts but frankly the guy I talked to was condescending and an ass) : http://www.schlenkent.com

Now granger has low tooth count (7 per inch) 4 foot sections (with a 1/4" bore pinon to match): http://www.grainger.com/Grainger/items/1L887 for around $65 but I wonder if this would be accurate enough for such small movements...


Hmm. That's crazy. We should keep looking into this. It seems like you would need very fine teeth for precise, small-increment moves. If you want to be able to run the thing vertically (boom move), or even at a significant grade, some type of fixed gearing is almost mandatory.

If you are simply wanting to move on a level track, rubber wheels resting on a monorail (with the weight of the car on top of the tires, applying downward pressure) might do the trick.


Mon Oct 20, 2008 6:52 pm
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Post Re: I made a new toy today
Good work! I have some questions about the different setups, especially the one with a friction wheel on the side of a PVC pipe - primarily, what are the smallest/slowest speeds you can accurately move like that? I'm wondering if there's any flex and/or play in the connection that would prevent extremely small motions from completing?

That is to say, I've found that if you take a motor attached to something its going to drive, and run at a certain speed for a certain time, you will get within 5% of your actual expected distance traveled at the end. I've been playing with my discrete motion setup, and have found that that 5% means that each motion may vary up to 5% depending on torque load, friction, evenness of the friction/drive plane, etc. Which is a little hard to predict for when doing discreet motions (motion between shots).

Even doing a straight gear setup, some slop in the mating of the gears results in loss of predictable motion - I can pre-load the initial backlash out, but occasionally the gears don't engage perfectly, and a number of movements are slightly off (still working on this) - this is mostly noticeable when making movements of about 1/10th of a degree and above.

I've spent some time thinking about the pipe/skateboard wheel design, whether driven via a direct-attached motor on a friction plane or via a pulley/cable system, and both keep coming up with issues for me doing this. Primarily that the starting torque of the skateboard wheels on the curved plane are different than running torque (takes more power to get them to move than to make them keep moving, due to a fairly high level of friction), and failing to make the tracks perfectly level resulting in nightmares with perspective...

We had talked about standard linear motion components before, and after some experimentation with some of them, I'm thoroughly convinced they are a better choice than the PVC/aluminum piping rigs. They are quite a bit more expensive than the PVC pipe route, but they are far more predictable and easy to get up and running without issue. Currently I've been playing with a single 20mm polished rod mounted on a T-rail w/ two bearing carts (http://www.vxb.com/page/bearings/PROD/2 ... ms/Kit7429 -- the bearings need to be swapped for higher-quality one as I find they freeze occasionally at starting, increasing starting torque and decreasing reliability of motion) - this low-cost solution works ok, but needs a second rail like the PVC designs to prevent roll (rotational slop) under torque. Going to order a second shaft soon, as an out-rigger to prevent roll, with the friction plane mounted lower than the two sides (motor/wheel sizing issues - bigger wheel = more friction + more discreet motion capabilities). The second rails doesn't need to have the T-support, it can use pillow blocks and a round guide block. In fact, both could be straight rail w/ pillow blocks. I purchased the T thinking it would have minimal roll - oops =)

If going this route, you could get rid of the second rail/outrigger all together by using T-style guide block and rail system (like those sold @ mcmaster-carr) and then you would just need a friction plane. However, the price would be nearly the same or even more expensive than using two less expensive rails and block sets.

So, kind of a silly question, but why not use side-mount track rollers instead of skateboard wheels? You know, like the kind they make for sliding closet doors? Would be easier/lighter than the PVC pipe and skateboard wheels setup. I think that design seems to be more oriented around the big dollies that are meant to be pushed by people, and are probably overkill/problematic for smaller-scale, precision motion control.

!c


Tue Oct 21, 2008 11:07 am
Post Re: I made a new toy today
tom wrote:
milapse wrote:
tom wrote:
maybe running some fine gear teeth down one side of the monorail?


Prepaired to be shocked... I looked into this (as I was convinced that it would be a 'simple solution') and was quoted over $2000 for a 12 foot linear rack gear! Maybe there is a better source... Here is the company that quoted that (they have beautiful parts but frankly the guy I talked to was condescending and an ass) : http://www.schlenkent.com

Now granger has low tooth count (7 per inch) 4 foot sections (with a 1/4" bore pinon to match): http://www.grainger.com/Grainger/items/1L887 for around $65 but I wonder if this would be accurate enough for such small movements...


Hmm. That's crazy. We should keep looking into this. It seems like you would need very fine teeth for precise, small-increment moves. If you want to be able to run the thing vertically (boom move), or even at a significant grade, some type of fixed gearing is almost mandatory.

If you are simply wanting to move on a level track, rubber wheels resting on a monorail (with the weight of the car on top of the tires, applying downward pressure) might do the trick.


You can get 32 pitch (32 TPI, roughly) racks in 6' length for ~ $42 from McMaster-carr.

To do vertical moves, you could just use stepping motors - they have extremely high torque at low speeds and also when not moving they lock quite well, preventing sliding backwards. Of course, you can brake any DC motor, but its holding torque will come into play, and is generally less than a stepper.

You make partial movements up the rack, but you can only guarantee a good hold if you're perfectly mated between the pinion and the rack tooth - meaning exactly meshed - so you would definitely want a higher pitch value. 32 is pretty good, but remember that only gets you 1/32" movements. You could use a pulley system fairly easily (although it would cost more), and get much better resolution - but you would have to sacrifice holding torque unless you used timing belts, and they have the same issue as a rack.

!c


Tue Oct 21, 2008 11:22 am
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Post Re: I made a new toy today
shutter, the Linear Guideway System looks pretty awesome. I do wonder, though, whether it might be susceptible to dust and dirt out in the deserts, etc?

Can you please show me a link to: "32 pitch (32 TPI, roughly) racks in 6' length for ~ $42 from McMaster-carr"?

Thanks!


Tue Oct 21, 2008 11:38 am
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Post Re: I made a new toy today
tom wrote:
shutter, the Linear Guideway System looks pretty awesome. I do wonder, though, whether it might be susceptible to dust and dirt out in the deserts, etc?

Can you please show me a link to: "32 pitch (32 TPI, roughly) racks in 6' length for ~ $42 from McMaster-carr"?

Thanks!


Yes, as the lube runs down the rail (it comes off the bearings) it will collect dust/sand/etc - the solution is to get sealed bearings/bushings that have a lip around them - they'll push the dirt out of the way. Here's one option: http://www.vxb.com/page/bearings/PROD/2 ... ms/Kit7411

McMasterr-carr doesn't seem to have direct links, go to "power transmission -> gears" and then scroll down the page.

!c


Tue Oct 21, 2008 11:49 am
Post Re: I made a new toy today
shutterdrone wrote:
You can get 32 pitch (32 TPI, roughly) racks in 6' length for ~ $42 from McMaster-carr.


Oh snap! nice find! I think that would do the trick... Tom it's PN: 6295k243 @ http://www.mcmaster.com Match two of those up with PN: 6325k89 (32 pitch - 16 tooth - 3/16" bore pinion @ $10) and you have a 12' geared track for $110 or so. NICE!


Tue Oct 21, 2008 12:55 pm
Post Re: I made a new toy today
tmophoto wrote:
i used skateboard wheels because i had a set i wasn't using and the the bearings are extremely high quality. there is virtually no starting friction on the setup that i have (I think it comes down to high quality bearings, i think mine are abec 5's) the actual contact are between the wheel and the pipe is tiny, close to a 2x2mm contact patch i would bet. also the PVC/ skateboard setup can be extended to 100' easily if i need it to be that long


Starting friction (initial torque requirement) would come from the contact of the wheels to the pipe, the primary friction caused by the uneven surface of both the wheel (which becomes less even as it is used) and the PVC (the same issue). It's basically the amount of torque required to get to the two surfaces to un-mate and allow the wheel to begin rolling. The bearings allow the wheel to spin around its axle with little friction, but that does not negate the friction between the wheel and the surface. A harder surface and harder wheel will reduce friction. Hence my comment about the standard linear motion components - they use a highly polished plane, and polished and greased bearings directly on that plane, resulting in minimal friction in general. Although, as you point out - starting friction is of little concern due to the fact that you're using a continuous motion setup.

tmophoto wrote:
the cart i built moves so slowly there is really no point in stopping it for the photos for my uses. currently i have it set up to move 5 feet in 2 hours 30 min, it can go as fast as 5 feet in 18 seconds and I am sure i could probably drop the speed to 5 feet in 5 hours by reprogramming it.

that rail guideway system looks amazing. I may need to get something like that or at least some of the bearing sleeves to play around with.

t


Have you tried working with long exposures? 30+ seconds? The reason I ask is because I went to a "discrete" motion system based around the desire to do very long exposures while also keeping a variable speed. That is, in long exposures, to prevent blur, you have to assure that no individual element in the photo moves further than 1 pixel during exposure. (Hence the tracking 'scopes, etc.) This would lock motion-speed to exposure-speed, such that you would have to re-adjust the speed based on your exposure time. Discrete motion prevents that issue, but creates the issue of having to tie exposure awareness (when the shutter is open and closed) to the motion-control system, which pretty much requires integration of the intervalometer and motion control system. It adds some complexity to design as well, but building one from the ground up is actually easier, imo - as I tried with continuous motion first, then had to destroy the device and start with discrete motion, it required less software in the end =)

Of course, I'm not in any way implying that continuous-motion systems are problems or incapable of doing great work - in fact, many of the designs are 'awesome' =) I'm just leaning towards discrete motion being more flexible and easier to work in the end. I'm going to post up some new software (for the AVR/arduino platform) soon that just lets you plug in the arc distance (e.g. 180 degrees) for each axis, "real time values" (e.g. 1hr), "output time value" (e.g. 30s), and exposure time (e.g. 1/15th sec) - and it will automatically map out the discrete movements, timing, etc. and run three steppers and a camera. Basically, when I was last out shooting - I got bored calculating timing, motion amounts, and all that jazz - and started changing the software to do all the heavy lifting for me.

tmophoto wrote:
sealed bearings will increase the initial stiction substantially, i think that kind of system would only work on a continuous motion system


These are used quite heavily in dirty machining environments for things like lathes and mills, that have a lot of stop-start motion (attached to a worm-drive, for example). Most of them are designed such that they don't actually increase friction (unless there's a lot of gunk on the plane) by being fractions of a mm off the plane its self. The tolerances are tight on the more expensive ones, and less tight on the cheaper ones (like VXB). You just have to get "close enough" as they say =)

!c


Tue Oct 21, 2008 1:50 pm
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Post Re: I made a new toy today
milapse wrote:
shutterdrone wrote:
You can get 32 pitch (32 TPI, roughly) racks in 6' length for ~ $42 from McMaster-carr.


Oh snap! nice find! I think that would do the trick... Tom it's PN: 6295k243 @ http://www.mcmaster.com Match two of those up with PN: 6325k89 (32 pitch - 16 tooth - 3/16" bore pinion @ $10) and you have a 12' geared track for $110 or so. NICE!


Very interesting! This might be the way to go.

If you built a monorail, using, say, 3" x 8" or maybe 4" x 10" aluminum rectangular tubing, you could put the gear racks on top, with skateboard wheels on top as well as on both sides of the monorail, providing several inches of distance between the car and the monorail on top. The spur gear then comes down out of the bottom of the car and engages the teeth on top of the monorail.

The reason this would be useful, rather than putting the teeth and gear on the side, is that you could disengage the gear drive and use the monorail dolly for free-hand motion picture shooting with a Red One, Red Scarlet, Sony EX1, or any movie camera.

shutter, i agree with you that "shoot-move-shoot" motion is mandatory. making a continuous-motion dolly is actually pretty easy. you could just pull the motor out of a grandfather clock and have it spool up some fishing string, dragging the car down any simple track. having a dolly that moves between exposures is best.


Tue Oct 21, 2008 2:40 pm
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Post Re: I made a new toy today
tmophoto wrote:
thanks for letting me know about the arduino platform looks like some good stuff. what is AVR system?

t


Oh, AVR is the line of chips Atmel makes - the ones running on the Arduino boards are of the AVR platform. (Differentiating them from the PIC uC's, Propeller, etc.)

BTW, I think you've done a good job so far on your project - I didn't want to come across any other way - just like discussing these things (not many other places we can have these conversations *grin*). If you start working with the Arduino, and run into any problems, let me know - I'm always glad to help! :D

As far as running the standard DC motors between shots -- you're right in that it's problematic, the DC motors will elicit less torque as they spin up, and especially running them at slow speeds (by reducing voltage or PWM frequency) will reduce their torque even more. So, you'd find they take a bit to actually catch and start moving the load.

!c


Tue Oct 21, 2008 6:08 pm
Post Re: I made a new toy today
tmophoto wrote:
no need to apologize this was my first attempt and i quickly found out it was not ideal, its always a work in progress and i am always open to suggestions. if we all work on this i think we can come up with an inexpensive solution that is rock solid and highly reliable.

so far i have nailed the inexpensive part but not the other 2.

t


Well, it will all depend on one's definition of "inexpensive" *grin*

Going with linear motion components, for a 55" run, it looks like the least expensive just for the rails and slides are about $300. If one is building everything else from scratch, it could go from about $250-300 in other components (expert skill level) to about $800 (limited skill level) for three axis. The price will be determined by how much one can design and build themselves vs. having to have built for them. All-in-all, I don't think it's that bad, since those rotary tables a lot of people are using are being sold at about $500, IIRC, and another $350 for the controller.

The trick is finding the right components and the right way to piece them together.

!c


Wed Oct 22, 2008 6:40 am
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Post Re: I made a new toy today
Well, digging up an old post.

Have you seen this rack & pinion drive assembly: http://www.cncrouterparts.com/product_i ... ucts_id=50 ?

Do you think it could work?

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Sat Mar 12, 2011 5:36 am
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Post Re: I made a new toy today
rikun wrote:
Well, digging up an old post.

Have you seen this rack & pinion drive assembly: http://www.cncrouterparts.com/product_i ... ucts_id=50 ?

Do you think it could work?


Hehe, yeah I know him - he's got a great product at a great price. It's a little beefier than some people would like, but its definitely a nice setup.

!c


Mon Mar 21, 2011 6:07 am
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Post Re: I made a new toy today
Those earlier posts are sure a blast from the past.

You will also have to factor in hi-voltage drives to get those sorts of real time speeds.
That particular rack and pinion system employs a narrow length of steel plate that must run the entire length of your profile to carry the linear bearing carriage.
It is sure beefier than just running the bearings inside the side channels of a profile.


Mon Mar 21, 2011 10:22 pm
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Post Re: I made a new toy today
Yeah,

That's the bad thing about his linear slides. With the steel plate they will weight a bit more than I'd like...

But you think the tooth profile and resolution would be good with that setup?

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Wed Mar 23, 2011 12:35 am
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