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 Mantis Previs move for "Offspring" series promotion 
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Joined: Wed Jan 20, 2010 4:50 pm
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Post Mantis Previs move for "Offspring" series promotion
Here's a good example of a long camera move designed in Maya.

The location was first mapped as a guide for the animator Mathew Makereth. The move file was then imported to Mantis, with the moco rig placed according to measurements from the Maya environment.

The move was then shot in segments - not in sequence unfortunately... This wouldn't normally be a problem, but because the move had to be tweaked in many places to adjust actors' timing and composition, I had to be careful not to corrupt in or out ranges from previous or forthcoming sections of the move. A lot of locks on keyframes were used... but generally the process was quite efficient due to Mantis's diverse editing features..




Left of the rig is DOP John Brawley - well known for his work with Black Magic Cine Camera. A Red Epic was used for the shot. I requested it cut down as light as possible, but still it ended up with an extra kilo of equipment and cables - mainly for the wireless follow focus... perhaps the head is a just a tad small for this rig, but it worked well...

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Tue Mar 25, 2014 5:29 pm
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Post Re: Mantis Previs move for "Offspring" series promotion
Great shot shows what motion control is for .So the move was built first i Maya so everybody happy with it then it was transported to Mantis ?
See what you mean about the Epic they do like loading stuff on to it . So one the other day in exactly the same state and was wondering it was all necessary . Way to big for my little rig .
Noticed you have markers on your axis . Is this for setting a standard zero or do you do that automatically with say hall effect sensors . Was thinking of going this route but not sure if it would be any more accurate than the little registration marks i have at mo .
Just realized way i think i am sticking to stop mo . Used to do commercials and what do they say never work with kids and animals . Frame at a time is a lot less stressful :D


Wed Mar 26, 2014 1:23 am
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Post Re: Mantis Previs move for "Offspring" series promotion
Yes - director and DOP approved the previs before the shoot and I was given the file in advance so I could check it would run ok. Lots more adjustments on the day...

Seems they can never load enough junk on the Epic... next time I might go with my own wired follow focus - it needs much less stuff than the wireless system.

For home positions I use tape markers on the motor shafts, as well as rough marks. Doing it on the motors is this only way to be truly accurate in case of a reset and to keep an eye on things during the day. It also helps if you have a back shaft on the motor to mount an inching knob. To use electronic homes would add even more cables to what is already complex enough!


Wed Mar 26, 2014 2:43 am
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Location: Hindmarsh Valley, South Australia
Post Re: Mantis Previs move for "Offspring" series promotion
Great work Gerald. It's interesting to see how using Maya to visualise the shot saves LOTS of money for the production. Didn't have that in my day (elderly man voice !).

How did you sync the rigs movement with the sync of the camera ? Not necessary ?

Steve R.

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Wed Mar 26, 2014 3:25 am
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Post Re: Mantis Previs move for "Offspring" series promotion
geraldft wrote:

For home positions I use tape markers on the motor shafts, as well as rough marks. Doing it on the motors is this only way to be truly accurate in case of a reset and to keep an eye on things during the day. It also helps if you have a back shaft on the motor to mount an inching knob. To use electronic homes would add even more cables to what is already complex enough!


Think i will follow your lead on that one. I too want to avoid to much clutter . Only problem with marks on motor shaft is if the timing belts jump and in my case they do in extreme circumstances . I thought this would be better than snapping lenses of camera bodies in a over enthusiastic tilt . But suppose its obvious if one marker on the motor doesn't correspond with the other on the tilt arm something is wrong .Problem is the more people who get hold of my rigs the more i have to be certain everything is fool proof and their are some fools out their :(


Wed Mar 26, 2014 4:09 am
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Location: Merritt Island, Florida, Estates Unitas
Post Re: Mantis Previs move for "Offspring" series promotion
Edward Teller once said "If you think something is foolproof, the fool is always bigger than the proof". Then he went on to give hydrogen bombs to idiots. So what does he know?

Clever quotable saying though.

Gerald, I am always impressed with Mantis. Seems like it can do more every day. You're making me want realtime movements more than I though I would. Thanks also for the pictures of the rig. I agree, you can hardly see the camera under all that stuff. Wish I had one.

That video is awesome by the way. I forgot I was watching for the motion, so I had to watch again. It plays out that well.


Wed Mar 26, 2014 9:49 am
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Post Re: Mantis Previs move for "Offspring" series promotion
Hi Steve

I think the previs artist spent a lot of his own time working on the shot, but it was time well spent. I checked the move though several versions and had to fix a few glitches in the transfer and apply a bit of smoothing to acceleration here and there but it was basically quite true to the plan - other than previously mentioned timing and composition adjustments. To program such a long move would have taken ages on set and tested everyone's patience. I gave him the rig parameters - which he applied to a virtual rig in Maya as a guide so he could see how it worked in the space, and could avoid going beyond the rig's limits.

Sync was extracted from the red frame pulse output which provides a TTL pulse at every frame. Mantis used this at the start of each run to synchronise to the shutter. I'm not sure how perfect it was in practice since I was not starting at the beginning of the move for each section - but seems like it was good enough for the compositors to work with..

Dman - re timing belts. I've never had one jump - that would imply that maybe the belt is not tensioned enough, or as you say an extreme situation. Some of my marks are on the input shaft to the gearbox - that can overcome the issue if it arises. I use a variety of belt profiles - AT5 T2.5 MXL and GT2 Even so it can be a source of anxiety keeping a check on things over the course of many takes. Accidents can happen due to operator error, cables snagging, or someone moving a stand into the path of the rig unexpectedly! I also make marks at the start or end of the move if time permits so the position can be confirmed before or after each take.

I'd love to have a more elegant system to find homes quickly. In theory it can be done but only with excessive complexity or expense. There are such things as absolute encoders that can read the position of a shaft to very fine degrees - but they cost... there are also schemes for an axis to search for home - but don't like the idea of the dolly moving up and down the track by itself looking for index marks!

G

Otherwise - it's hard to imagine a truly foolproof rig. Some people can be trusted to undermine even the most bombproof system!


Wed Mar 26, 2014 5:28 pm
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Post Re: Mantis Previs move for "Offspring" series promotion
So does the TTL pulse from the camera supply the timing for the whole process or just as a start point ?

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Wed Mar 26, 2014 7:14 pm
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Post Re: Mantis Previs move for "Offspring" series promotion
Hi Steve The camera outputs the pulse continuously when running - so you roll the camera, then roll the moco, which looks for the edge of the first pulse it sees, then starts the move. After that there is no more checking required, since both camera and moco have crystal time bases and will stay in sync for a considerable period. So short answer - it's just a start point...

In the days of Kuper the moco also had to keep tabs on the pulse during the shot - that was necessary in the days when not all film cameras had crystal locked motors.

The same routine can be used with a video signal from the camera, provided the video monitor is in sync with the shutter. On professional cameras this is the case, but DSLR's don't have a consistent sync between their shutter and the monitor output... so it's not possible with the majority of DSLR's. I have tested a 5D for example and found I could get sync about every other 2nd or 3rd run - it seemed a bit random... :(

It is also possible to sync in reverse. ie. generate a pulse per frame from Mantis (or an independent sync generator) and lock the red camera to that. I don't use it in practice though because the Red will behave badly in this mode. If the sync source is disconnected then Red will appear to lock up. It's actually looking for the sync signal and only refreshes itself when it sees a pulse. This is just plain annoying and disconcerting...!


Wed Mar 26, 2014 8:24 pm
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Post Re: Mantis Previs move for "Offspring" series promotion
I'd gathered it would be fine as a starting point. I've used my old rig (just dolly) with a 5D2 for some multilayered, matte shots without any sync with the camera and it was fine. Well fine at SD resolution. :-) I had a basic audio sync which start the rig based on music. It was for a film clip I did of my own music. I had a sync pulse which would start the dolly moving based on placement within the music so I was actually playing along at the musically correct position. Fun stuff.

_________________
Amongst Myselves - ambient, landscape and space music
Canon 5Dm2, 450D, 17-40mm EF f4, 70-300mm L, 50mm f1.8 EF, Custom Intervalometer (UM9 and UM12) and MOCON, Meade LXD75 SN10


Wed Mar 26, 2014 8:53 pm
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Post Re: Mantis Previs move for "Offspring" series promotion
geraldft wrote:

Dman - re timing belts. I've never had one jump - that would imply that maybe the belt is not tensioned enough, or as you say an extreme situation. Some of my marks are on the input shaft to the gearbox - that can overcome the issue if it arises. I use a variety of belt profiles - AT5 T2.5 MXL and GT2 Even so it can be a source of anxiety keeping a check on things over the course of many takes. Accidents can happen due to operator error, cables snagging, or someone moving a stand into the path of the rig unexpectedly! I also make marks at the start or end of the move if time permits so the position can be confirmed before or after each take.

I'd love to have a more elegant system to find homes quickly. In theory it can be done but only with excessive complexity or expense. There are such things as absolute encoders that can read the position of a shaft to very fine degrees - but they cost... there are also schemes for an axis to search for home - but don't like the idea of the dolly moving up and down the track by itself looking for index marks!

G

Otherwise - it's hard to imagine a truly foolproof rig. Some people can be trusted to undermine even the most bombproof system!


Hi Gerald the jump is a conscious thing after years of having Land Rovers i prefer a half shaft to brake rather than a gear box :D .
What gives on your rig when it meets a immovable object . Are your drivers clever enough to cut out under extreme loads. That would be handy specially when these rigs are getting bigger and bigger . In stop frame mode its very hard to tell if any damage is been done until its to late and the steppers have a lot of torque at such slow speeds .
As for home switches we got one of those cheap laser cutters at work and its got hall effect sensors for limit switches . Will try and test how accurate they are if i have a spare moment . The plus side of them is the wiring feeding them can be very thin so i don't think it will clutter to much . The reason its sort of a issue for me is shoots are some times left over night in animation . Which means in a perfect world the rig should be a able to home and reset itself exactly . Mind you i suppose that's why you pay a lot more and get yourself a Mark Roberts Rig .
D1


Thu Mar 27, 2014 12:02 pm
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Post Re: Mantis Previs move for "Offspring" series promotion
Re hitting limits - Generally I always set the motor currents so they are strong enough for the job, but if they hit a limit they will stall. All belts and gears should be strong enough to withstand this. I've never damaged a gearbox or rig or even a camera yet... sometimes I have dented a set though... especially the polystyrene type...

If you use servo drives then you have more options - they will cut out as soon as they are out of commanded position by a preset amount.

For overnights it's preferable to leave everything powered up, or just disable motors without turning of the power. Otherwise - You can just mark where you are, and after turning back on, recheck the marks. (Mantis can re-initialise the position for you without needing to return to home.) Also shoot a reference frame in the camera.

Steppers will often kick a little when turned on - so you may need to readjust. Mostly you'll find something in the set has moved though - especially any timber...


Thu Mar 27, 2014 3:44 pm
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