Searching the internet about camera movement – I tried the phrase motion control curved track.
Viewing the search results in Images mode, I found a few interesting pictures at http://www.general-lift.com/Services/curveTK.html
Getting a camera to move around an object – can become a big production effort…
Got the idea to just move the tripod – with the camera sitting on top. Probably been done a million times before, but for my simple projects, having a nice smooth surface or floor to drive on – would be just fine…
After thinking about how to make this “tripod dolly” – there were several desired requirements.
Making it move forward or backward – needs one motor. Being able to steer it – requires a second motor. It needed to have a low center of mass – which keeps the Gitzo tripod, as close the the ground as possible.
It also needed to be strong – perhaps being able to hold a couple hundred pounds (66 lbs x 3 areas of contact = 198 lbs). And I wanted something simple – for keeping the 3 tripod legs from slipping off the dolly. Nor a complicated clamping mechanism. And if one wanted to use a tripod at its lowest height – it could easily adjust. One could even remove the tripod and attach the camera directly to the frame, making it operate – just a few inches above the ground.
I envisioned this “dolly” moving down a hallway, then going thru a doorway, into another room. Assuming I come across a narrow door frame with an opening of 36 inches, this “dolly” could pass thru it. So for the maximum width – this device could be no more than 34 inches.
Last fall, I went to the Okotoks Salvage Center, and looked at their collection of roller-skates. Purchased 3 used sets for $10. That’s a total of 24 wheels.
One set was exactly like the ones used on the Slider. Picked 4 of the 8 for this project. Once I inserted the 2 inch long bolts thru the bearings and spread the 2 wheels apart – I now had the desired length of the side-plate, which was 5 inches. After those 2 plates were cut, four 0.25 inch holes were drilled and the bolt heads were mig welded.
A 31 inch long piece of 1.5 inch angle iron, was cut. The two end plates, were then welded on. Two tripod legs would sit in those two corners – with good support on the side, back and bottom.
The excess bolt threads – were cut off with the zip blade – flush to the nylock nuts. That gave me the overall required width of 34 inches…
The next task, was to add another piece of angle iron and rotated so that the 90 degree inner angle – would face up. This would make a V channel – for the 3rd tripod leg, to sit in.
If one adjusts the tripod legs, so that all the leg bottoms are 31 inches from each other, then marking the mid-way point between the back two legs – is 15.5 inches. If one now measures the distance from this point, at 90 degrees and towards the 3rd leg, this length is only 27 inches. The “T-Bar” piece was cut to 27 inches and welded in place.
Each corner is now 31 inches apart, and forms a triangle – just what a tripod was made to do… 🙂
Next task was to design and build the drive system. For added stability at the front end, I decided to use two large 6 inch plastic wheels (with a rubber coating on the outside rim). Figured that a 3 inch gap between them, would still allow for a decent turning radius. Plus I needed some room for the clamps – which will hold the wheels, and room for the big chain gear – mounted in the center of the axle.
I also ordered extra gears, since I didn’t know exactly which set of gears, would provide the best performance – a combination of torque and speed ratio.
The wheels came with 1 inch diameter centers, so a 1×6 inch aluminum tube was used for the axle. A few extra clamping devices were added, just to keep everything from shifting…
At this point – I still didn’t know the best location to mount the 12 volt DC drive motor (somewhere above or in front)…
There are lots of ways to attach an round axle, but I decided to use square bearings… 🙂
Found some scrap steel flat bar, used a torch to heat and bend it to the desired width. From there, I had to measure how much of a gap I wanted above the wheels…
On the top face, I drilled a 0.5 inch hole for a bolt – that would pass thru a 1 inch bearing, located above and inserted into the Riser Arm.
Once this Steering Fork was kind of figured out, I could then get a rough measurement of the height and reach needed – for the front Riser Arm.
Found another thicker piece of flat bar – that was heated and bent to a 90 degree angle. The biggest bit I had was 7/8 inch. Had to use a die-grinder to finish making the hole to a 1 inch diameter. A 1 inch bearing would serve as the steering pivot point.
Close-up of the cuttings. At least the bit was sharp…
Here’s a quick assembly of the Riser Arm, holding the Steering Fork.
Next was to mark and cut slots in the Steering Fork – where the two square bearings would be located.
Removing the center section is a bit of a chore…
With careful cutting and hand-filing of the slots, both bearings have a tight friction fit.
With the steering mechanism assembled, a quick test was done – to join both sections with a magnet. Each end of the 90 degree Riser Arm – had extra length – to allow for design changes. Now that everything looked good, the excess material was cut off.
Found a large double pane window, which would keep all the wheels sitting flat. The concrete floor was fairly rough and uneven…
Once I had the T-Bar parallel to the glass, the free end was welded to the back side of the Riser Arm. I then was able to position – where the 4 inch linear actuator would sit. Another vertical flat bar was cut, bent and welded onto the T-Bar. The back-end of the actuator would attach to this bracket.
Everything was then taken apart, the main frame cleaned and painted…
After 3 coats of spray paint, the frame was ready for re-assembly…
A short piece of angle iron was cut, fitted and welded – onto the front edge of the Steering Fork – just off center. The 4 motor-mount holes were drilled and the drive motor attached. Ended up making 3 different chain lengths, before I found the right gear combination. A bolt was welded on the side of the Steering Fork, for the front-end of the steering actuator motor.
Wires were quickly connected and a test was done, using the Motor-Mixer.
Here’s a shot of the Tripod_Dolly being used in a recent project…
