DIY Dolly Track

[caerus_sam]

Hi guys,

Hopefully I'm in the correct neck of the woods here! I'm currently working on a DIY Dolly Track for some video work, but I'm also going to be utilising it for some timelapse photography over night (The imagine below is what I'm working towards, not the actual Dolly Track). I will be motorising the Dolly Track to assist in making my life easier, but I have a slight concern over timings. Would I need to add a delay in to the motor circuit to account for the time delay in recording the images, or would it all seamlessly blend in to one? As an example, if I shoot for 30s, and the delay between shots is 15s, would that 15s be noticeable whilst tracking the camera?

It seems a bit wrong posting this question here, but I will also use the thread to document and show you the Dolly Track as it gets completed.

TIA and all the best,

Sam.

[Gweedo]

That's clever, that is.  I like it!

[Squagnut]

I assume you mean the dolly will be moving only during the 15s interval? If so, it depends on how far the dolly moves in 15s and on how distant your subject is. For the night sky it shouldn't be an issue, but for something much closer you'd probably notice the jump.

I like it! Are you planning to use a long belt drive?

[caerus_sam]

Yes, just the dolly. Sorry for not clarifying that! I think it'll just be generic widefield shots for the night sky, nothing up close and personal. During the daytime, I'll more than likely use a normal video camera for that, so it's just the night sky that'll use the DSLR. 

I'm looking in to belt drives, but I might go for something a bit simpler. I'm considering utilising motors and drives already available to power the setup, something like this: http://www.firstlightoptics.com/celestron-mounts/dual-axis-motor-drive-for-cg-4-and-omni.html In my minds eye, it'll just be a simple case of mounting some sprockets and then attaching a belt, but I'd be interested to hear what you guys think. The advantage of this would be the low rpm of the motors. Assuming they're 1rpm motors to match the rotation of the Earth, the lateral distance covered should be around 2in per minute (ipm). That would work out to be around 30 minutes to cover the distance of a 5ft slider. 

I'm sure I have more in my head, but putting it in to words is a bit difficult at the moment.

All the best,
Sam.

[caerus_sam]

..further to my last, it can be done. 

http://youtu.be/DsER8q7gWzk
 

The guys is using an Igus DIY Timelapse Dolly with a Skywatch EQ-1 motor mount to power the slider. That's given me hope that it's possible!
 

[caerus_sam]

..and again. I do apologise! 

Just looked at the EQ-1 Motor Drive on a few websites and noticed that a lot of people are using them to power DIY Dolly Sliders. Being a single axis unit, it saves any unnecessary faffing about, which is always a bonus, and the built in ability to regulate the speed helps too!. This guys review caught my eye, because it gave a little insight in to the distance I can cover dependent on rpm the speed selected: 
 

: I bought this to move my camera along my slider for timelapse photography. Did the trick well. Need to gear down between the motor drive & the slider to slow things down further, enabling me to do longer timelapses over a period of 8 hours or more. Currently will move the camera over the 31 inches in 1-4 hours, depending on the speed dialed in.

It's looking promising! Now, to figure out mounting and how to actually get the slider to move in step!
 

[Psychobilly]

Flexible toothed timing belt and pulleys driven by a stepper would be my first choice....   We used to have some very high precision and fast motion control systems usign that drive mechanism...

Peter...

[Squagnut]

Yeah, I must say steppers give more precision, if precision is important, and it'd cost a lot less than that DC setup for the CG-4.

But then, I tend to think that Arduino is the answer, now what's the question?! It'd even be fairly straighforward to synch in the camera.

I've had a good look at making a slider, and of the three main ways to make the dolly move - belt drive, archimedes and toothed track - I favour the toothed track. But all methods have advantages and disadvantages.

[Psychobilly]

I have built Precision linear slides  in the past using re-circulating ball mechanisms and a 3m x 3m XY system  that was belt driven with a 3rd rotary axis that was also belt drive ... The advantage of toothed belt is that it is easy to split the track into sections the end of the belt can be clamped on the moving "trolley" and a simple sprung belt tensioner mechanism use dto take up any slack....

Peter...

[dtokez]

very impressive - where did you get the parts for the rail?