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 Designed My Rig, Questions Before I Buy & Build (Updated) 
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Joined: Thu Feb 10, 2011 1:35 pm
Posts: 23
Location: New Orleans, Louisiana, USA
Post Designed My Rig, Questions Before I Buy & Build (Updated)
[Edit: After getting some feedback and subsequently doing more research, I have abridged this post down to only what is left unanswered]

First off, let me thank everyone who has contributed to these forums as it is truly a wealth of information for anyone trying to build a motion control system or get into time lapse videography. I have tried to educate myself as much as possible before posting but I would like the community's feedback on my rig's design before I buy the parts.

I am directing a documentary in which I would like to do some time-lapse tracking shots, both horizontal and vertical.

This system will be built around the PBC Redi-Rails Low-Profile Linear Bearing. I chose this because it seems to "glide" better for using the slider for conventional tracking shots (non-timelapse). The motor/gearing will be similar to this prototype (http://openmoco.org/node/126) but I plan on turning the belt perpendicular to the guide rail (see image of mock-up).

Project Goals:
-Slider must work "manually" as a traditional slider operated by the camera operator's hands on the pan/tilt head--no motors or cranks
-With belt engaged, slider will shoot "stop, move, stop" style time-lapses and will be capable of vertical tracking (final shots will range from 3 to 10 seconds, time lapse periods will range from 10 minutes to 2 hours and carriage will travel up to 6 feet/72 inches)
-If possible, operator will have ability to manually control dolly move w/stepper driver/stepper motor for very slow tracking shots, macro tracking shots and remote mounting situations (I can add electronics to do this at a later time)
-Target budget: ~$500, a little more if necessary

Gear List (full gear description available in PDF packet linked below):

Part/Part or Model#/Qty/Unit Price/Total Line Price

Redi-Rail T Slot Low Profile Carraige G-RRL34C-B2-019F-C0 1 83.4 83.4
Redi-Rail Low Profile Guide G-RRL34R-072.000-R0 1 193.75 193.75
Anneheim Automation - 17YPG Stepper Motor w/Planetary Gearbox (19:1, 62oz/in torque) 17YPG302S-LW4-R3.7 1 83.6 83.6
8mm Bore, 16mm Outside Dia., 440C Stainless / ISO 6 Ball bearing, lube with Oil A 7Y 5MFSS1608 4 11.41 45.64
Polycarbonate Belt clamp for single and double sided belts A 6M53M060 1 5.16 5.16
3 mm GT2 Pitch, 6mm Wide, Open ended Neoprene Belt A 6R53MC060 4 9.81 39.24
8 / 8mm (Side1 & Side2), Zero Backlash Miniature Slit Type Flexible Coupling. S50MSXM19P08P08 1 22.31 8.66
GT (3mm) Pitch, 45 Teeth, Aluminum alloy Timing Pulley A6A53M045NF0608 2 0
8 (-.005/-.014) Dia, 50mm Long, 303 ST. Steel Shaft A 7X 1M080050 1 3.59 3.59
8 (-.005/-.014) Dia, 65mm Long, 416 Stainless Steel Shaft S40PX0MHG8M-065 1 5.92 5.92

+Arduino board, battery and other necessary components

Here are images of two possible designs using mostly the same parts. I will try to fit the belt underneath the carriage but if there isn't room I will opt to run the belt alongside the guide rail:
Image
Image

Questions/Concerns:


Specific Questions:

1) The maximimum torque of all variations of the 17YPG stepper from Anaheim Automation is 1250oz/in but the bipolar torque ranges from 34 to 100oz/in. Being that the stepper will be stopped when it needs to move, does it matter what the bipolar torque is? Can I get the lowest torque or should I opt for higher?

2) Is the 6mm wide, 3mm GT2, 333 teeth per meter belt and corresponding pulley adequate for doing vertical-tracking time lapses? (will it have enough bite to hold the carriage with Sachtler head, canon 5d or 7d and wide-angle lens or will I need bigger teeth and/or a wider pulley?)

3) Does anyone know of a tutorial on adding the necessary components to the Arduino to connect the camera and stepper motor(s)? I haven't been able to find any instructions on doing this specific to Openmoco. I feel like I must be overlooking it.

These forums have opened up a lot of possibilities for me and I am very grateful for all the info and anyone's help with my specific questions. THANKS!!!

PDF Packet with designs, and all details on parts: PDF Packet


Thu Feb 10, 2011 1:45 pm
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Joined: Tue Jul 08, 2008 12:36 pm
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Location: Antarctica/California/New Zealand
Post Re: Designed My Rig, Questions before I Buy & Build
There are others here who can probably better answer the specific engineering questions you have, but a couple of quick notes from me to get you started...
I think you basic design looks pretty sound. I would probably go for the centered belt personally to keep it out of the way and less prone to interference during a shoot.
You should be able to figure out your move distances with a bit of simple math based on the stepper movements and the gear box ratios.
If in doubt, yes, shoot a much faster frame rate than you think you will need, you can always speed it up in post, and it will allow you lots of options for the final "Look" of the finished clip depending on how you process it.

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Thu Feb 10, 2011 3:54 pm
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Joined: Thu Feb 10, 2011 1:35 pm
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Location: New Orleans, Louisiana, USA
Post Re: Designed My Rig, Questions before I Buy & Build (Updated)
Thanks for your reply. I have done some more research and think I understand a little better now. I updated my original post, leaving only the specific parts questions. Anyone?


Fri Feb 11, 2011 7:47 am
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Joined: Fri Dec 24, 2010 8:26 am
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Post Re: Designed My Rig, Questions before I Buy & Build (Updated)
Looks like a cool design! Sorry, I don't have enough knowledge to answer any of your questions, but I have one of my own:
What is the advantage of using a looped belt with the motor fixed at one end versus putting the motor on the carriage and fixing the belt at each end of the rail? It seems like the looped belt/fixed motor design has more parts, and thus more cost, involved.


Fri Feb 11, 2011 10:29 am
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Joined: Thu Feb 10, 2011 1:35 pm
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Location: New Orleans, Louisiana, USA
Post Re: Designed My Rig, Questions before I Buy & Build (Updated)
harmonic_exposures wrote:
What is the advantage of using a looped belt with the motor fixed at one end versus putting the motor on the carriage and fixing the belt at each end of the rail? It seems like the looped belt/fixed motor design has more parts, and thus more cost, involved.


Thanks harmonic.

I considered doing an "omni design" with the motor mounted on the carriage but I opted to keep the weight and size of the carriage down in case i want to use a heavy lens and/or tripod head. I use an expensive but great sachtler tripod (about $6000) and didn't want to have to buy another cheap head, especially since I plan on using this thing out in the swamp. Also, I want a design where I can easily disengage the belt and use the slider manually. I suppose this could be achieved with an omni configuration but I like the looped configuration better. My only concern is that a smaller belt that could run underneath the carriage won't be heavy duty enough for vertical tracking.

I'm also not crazy about having to run so many wires to the moving carriage. If I was going for a time lapse-only rig like the dynamic perception, I would probably go with the omni configuration, heck, I would probably just buy the dynamic perception package but I really want a great slider for traditional real time tracking shots, which I forsee myself doing much more often than time lapses.

In terms of cost, the additional belt length, pullies, shafts and bearings you would need don't cost that much relative to the cost of the linear bearing itself. For an omni setup, you would need to make the carriage bigger and clamp the belt at each end, which would incur costs as well.


Fri Feb 11, 2011 12:18 pm
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Joined: Wed May 27, 2009 5:10 pm
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Post Re: Designed My Rig, Questions Before I Buy & Build (Updated)
I'm also about to order parts for my dolly. It's going to use the omega-drive.

I was just wondering wouldn't it be beneficial to use a Trapezoidal belt, since they are designed for linear motion?

I'm also considering using a long trapezoidal lead screw (it's a metric Acme) instead of the whole belt-drive, but I'm not sure of the advantages / disadvantages of such approach?

I'm assuming it would do vertical moves a lot easier than a belt-driven dolly? I already have anti-backlash nut for it and some other stuff from dumpstercnc...

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Wed Feb 23, 2011 8:43 pm
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Joined: Wed Nov 11, 2009 10:45 am
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Location: Merritt Island, Florida, Estates Unitas
Post Re: Designed My Rig, Questions Before I Buy & Build (Updated)
Sorry that I too am incapable of answering your three remaining questions. That hasn't stopped me from typing my two cents worth anyway. If you are concerned about the belt not fitting under the carriage, you'll get more room by laying the belt flat on the rail instead of supporting it on edge (perpendicular to the rail). I have found that the belt can sag a bit if you substitute rediculously long rails for the convenient 6 footer the DP dolly comes with. The sagging belt likes to ride up on the edge of the toothed pulley. I have never had this effect a run, or drop off the pulley entirely, so it hasn't become a functional issue. A dolly where the belt lays flat on the rail wouldn't have this potential problem lurking.

I am a big fan of the dynamic perception dolly in spite of the above comment. Is there some reason why you want to go through all the trouble of reinventing the wheel (or teflon slider)? You can easily pull the DP slider manually for real time shots by just not connecting the belt. If you want slow, smooth, silent motorized movement for full motion video with sound, just get a long belt and mount the motor off of the dolly track. Attach the belt to the dolly slider. Place the motor and toothed pulley on a tripod or some support a short distance beyond the end of the track and use the belt to pull the trolley along the rail. It is almost completely silent in this arrangement. This also takes the small weight of the motor off of the trolley if that is a concern for you.


Mon Feb 28, 2011 9:14 am
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Joined: Wed May 27, 2009 5:10 pm
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Post Re: Designed My Rig, Questions Before I Buy & Build (Updated)
I'd say the belt width seems a bit small... It might cut it, but over-engineering a bit when in doubt is always a good idea :-)

I'm doing something a bit similar, for very heavy loads (60-100 pounds of payload) and I'm probably getting a 16mm AT5 gear. I was considering a 10mm variant, but the price difference is small.

But then again, that Redi-Rail is very low-profile, you probably can't fit very wide belt inside...

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Sun Mar 20, 2011 8:28 am
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