I've been having fun making and then improving my attempt at a time lapse dolly over the last few weeks, much to the ammusement of my wife
My first attempt use a geared motor from Jaycar which did 60 RPM. This turned out to be way too fast, so I found a 2 RPM motor on eBay for $12 which is much better, but still completes my current length of 3m track in about 40 minutes, a little faster than desired.
I use a 12v dew heater controller to power the motor and alter it's speed (as much as possible - not much). In reality the dew heater controller is actually one of the Jaycar motor control kits.
Also, my first attempt had a much smaller wheel base, smaller piece of pine I built it on. I quickly realised the weight of the camera needed a much wider platform to balance on.
I still need to work out a spindle for the motor. At the moment I just have a spare William Optics focus knob on it because it has the same shaft size, but I need to get a spindle made to wind the rope on to.
The two rails it runs on are extendable tent poles, this provides for some nice flexibility in travel distance, and I can easily extend them with another two I have to get about 7m travel.
When in use I set it up on two carpentry horses I have. If it works well I might buy two cheap tripods to use in the field instead.
Interesting stuff Roger. I was considering doing something similar using Jaycar's 12v 36RPM motor (YG2734) at 2 volts it's doing a bit under 5rpm - feels to have reasonable torque and starts reliably at that voltage.
Would it be possible to reduce the supply voltage to your motor to slow it down a little?
edit> microwave oven carousel motors are good for hi-torque low rpm applications (2.5rpm (iirc)) but of course being 240 volt, they introduce a bunch of other problems.
The catch is if the motor will operate at such low voltages (well enough t pull the dolly). I am finding the motors need a minimum voltage, for the 2 RPM motor the lowest voltage I can operate it at is about 5v, which results in a speed of one rotation in 43 seconds, so slower than 2 RPM. The jaycar motor was the same, I found I had to have thevoltage higher than 2v, I didn't measure it but probbly about the same 5v too.
Roger.
Quote:
Originally Posted by michael_sa
Interesting stuff Roger. I was considering doing something similar using Jaycar's 12v 36RPM motor (YG2734) at 2 volts it's doing a bit under 5rpm - feels to have reasonable torque and starts reliably at that voltage.
Would it be possible to reduce the supply voltage to your motor to slow it down a little?
edit> microwave oven carousel motors are good for hi-torque low rpm applications (2.5rpm (iirc)) but of course being 240 volt, they introduce a bunch of other problems.
Michael, reducing supply voltage on its own reduces the overall torque and quite dramatically once the voltage reaches a certain point.
The correct method is using PWM (Pulse Width Modulation). This allows the motor to receive full voltage (for torque) while producing spaces of nothing to reduce speed. It is not perfect and the correct PWM is quite complicated but overall produces a far better result than a simple reduced voltage.
The correct method is using PWM (Pulse Width Modulation). This allows the motor to receive full voltage (for torque) while producing spaces of nothing to reduce speed. It is not perfect and the correct PWM is quite complicated but overall produces a far better result than a simple reduced voltage.
Instead of reducing the speed of the motor, control it through an intervalometer to run for say, 10 seconds between camera exposures.
If I understand the technique correctly, there is no need for the camera to track during the exposure, but just to be in another position at the next exposure.
Another good option if you like electronics is to use a stepper motor which is controlled by an Arduino. The following website has some stepper motors including geared steppers:
Very cool And simple Roger. The wheels look intriguing , what are they ?
They're small caster wheels like you have on the bottom of office chairs. I wanted something which would ride over the rail and this was the best I could find .. I would like an option which sits even more over the rails, like wheel rim, but haven't found a suitable one yet.
They're small caster wheels like you have on the bottom of office chairs. I wanted something which would ride over the rail and this was the best I could find .. I would like an option which sits even more over the rails, like wheel rim, but haven't found a suitable one yet.
Roger.
Thats an excellent idea. Are the edges sitting on the rail smooth enouGh for smooth motion?. You could use generic fat rubber tired wheels and take the rubber off,but they are much harder to mount (axel) and I don't think the motion would be any better.
Short wide angle exposures are fine with slow continOuse motion. Stop start control woulnt be hard though. A simple timer that stopped the dolley on the off part of the cycle and triggered the cam(on auto expose) at the same time would do. A timer with double pole relay output would do the trick. One pole to turn the motor on and off and the othe pole to trigger the cam at the same time.
Thats an excellent idea. Are the edges sitting on the rail smooth enouGh for smooth motion?. You could use generic fat rubber tired wheels and take the rubber off,but they are much harder to mount (axel) and I don't think the motion would be any better.
I did get one of the red ones I think you're talking about, from Bunnings ... I found when I pulled the rubber off that the rim has plastic ridges across it, 4 around the rim. I considered grinding them down with the Dremel but didn't think I'd get a smooth enouth result. If you know of any that don't have the annoying plastic ridges I'd love to hear I bought one to see what it was like, haven't tried them all.
I am yet to crtically test it. The trials I've done it's perfectly smooth. I think maybe the fact that the wheels can spin horizontally means they align themselves nicely with the rails to a degree, which makes the trolly a bit more stable and smooth running.
I used the bunnings red wheels but left the rubber on (the rails had edges for guiding) but had the same problem with moulding ridges and bumps on them. I've looked at many cheap hardware store wheels , they are all the same, all required dremmel work to make smooth. They are cheap for a reason, not made for ultra smooth travel unforch. Smoothing them isnt easy either. I'm resigned to getting proper industrial ones now, when I get round to it.
I have seen Fred's marvelous "machine" and watched it in operation. What a joy to watch!
I think his aim was to use readily available parts so that the idea could be duplicated by anyone with the minimum of facilities.
If I ever get interested in that sort of photography I would be inclined to use my engineering expertise in live steam railway modelling and my workshop to build something from prototypes made from Meccano (another of my hobbies). Maybe I can find solutions to some of the drawbacks.
as for the wheels, you could use two hole saws of two diameters to drill out two cores from a ply piece. just glue them together once aligned. very simple source of wheels.
the hole saw kits are available in bunnings for 15 odd, so use say a 20mm first and take out the core, then use a 34mm and take out the core. align the two and use liquid nails. that will give you a wheel with an inner flange. just use the non threaded part of an m6 bolt as the wheel axle.
also, if you tie the thread at both ends with just a few turns on your motor shaft for grip, that will allow it to move in both directions. something like a scanner assembly. you can even spring load it at the ends.
if you're handy with electronics and soldering, you could easily rig up a 555
based variable oscillator, use this stepper controller that can do 1/16 microstepping, and get a stepper motor. that will get the movement slow and smooth.
Thanks for those, I think I will get one to try it. Quite affordable.
Quote:
Originally Posted by alistairsam
as for the wheels, you could use two hole saws of two diameters to drill out two cores from a ply piece. just glue them together once aligned. very simple source of wheels.
the hole saw kits are available in bunnings for 15 odd, so use say a 20mm first and take out the core, then use a 34mm and take out the core. align the two and use liquid nails. that will give you a wheel with an inner flange. just use the non threaded part of an m6 bolt as the wheel axle.
Brilliant idea, thanks. I already have suitable hole saws and wood so will do this if I find I have problems with the current wheels not gripping the track securely enough.
Quote:
Originally Posted by alistairsam
secondly, if you fit a second motor under the camera and manage to get it very slow, you could pan as well.
Yes... have thought of this.. perhaps revision C when I rebuild it again for more functionality
