GraBird
Member
I just built the dolly from Dan Selakovich's terrific book "Killer Camera Rigs That You Can Build" http://www.dvcamerarigs.com. But I wanted to add three PVC caps to hold the tripod legs firmly in place, positioned so that the tripod head bolt is perfectly dead center on the dolly.
After a few frustrating moments trying to remember those very basic high school algebra principles :undecided, I found a great site with the simple way to do this:
http://www.salsburg.com/cadfaq/geometricconstructions.html.
(Look at the third drawing in section B.)
Here's the finished results:
I found dead center on the board first (marked as CTR). I inserted an eyehook at this spot. (Later this will be a hook for a bungee cord, attached to the tripod head area so that tripod's not going anywhere even if I've got the dolly on an angled track or in the event the dolly takes a bounce off the tracks.)
Then I used a string to draw a perfect circle around that point. On the 24" wide dolly, I think I ended up with a radius of about 10.5" (21" diameter).
Mark the first point at the "front" of the dolly. This is easy. It's just the point where the center of the board width intersects the circle. (On the image, it's the PVC cap near the words "RADIUS 10.5".)
Next, find where the center point intersects that circle at the back of the dolly. This is indicated on the image as A, and it's basically the point on the circle that's opposite the front point.
Now it's a simple matter of drawing a bisecting arc from that point, one which passes through the center point. Or in simpler terms, measure from point A to the points on the circle that are 10.5" away from it.
I did a spot check on the measurements, to check how far each cap point would be from each other around the equilateral triangle, and what do you know -- it's approximately 18" from point to point! Very cool!
I drilled a hole through each 1-1/2" PVC cap (actually off-center and at a slight angle) and screwed them into the board at these points.
So now the tripod legs can seat securely into those caps and a bungee cord down to the center point pretty much fixes the tripod firmly onto the dolly.
And the tripod is perfectly centered on the board!
(The wheels look out of whack, but it's just the camera angle, they're actually nice and straight.)
_________________________
The three holes at the back of the board allow attaching strings. (I have a shot planned where the dolly track will be on a downward incline, so this will allow me to just slowly feed the string out and let the dolly smoothly roll down towards the subject for a close up.)
I still plan to add a couple of handles for easier carrying.
(Now with DIY project #1 done, it's on to the "SteadiCam" stabilizer next!) :cheesy:
After a few frustrating moments trying to remember those very basic high school algebra principles :undecided, I found a great site with the simple way to do this:
http://www.salsburg.com/cadfaq/geometricconstructions.html.
(Look at the third drawing in section B.)
Here's the finished results:
I found dead center on the board first (marked as CTR). I inserted an eyehook at this spot. (Later this will be a hook for a bungee cord, attached to the tripod head area so that tripod's not going anywhere even if I've got the dolly on an angled track or in the event the dolly takes a bounce off the tracks.)
Then I used a string to draw a perfect circle around that point. On the 24" wide dolly, I think I ended up with a radius of about 10.5" (21" diameter).
Mark the first point at the "front" of the dolly. This is easy. It's just the point where the center of the board width intersects the circle. (On the image, it's the PVC cap near the words "RADIUS 10.5".)
Next, find where the center point intersects that circle at the back of the dolly. This is indicated on the image as A, and it's basically the point on the circle that's opposite the front point.
Now it's a simple matter of drawing a bisecting arc from that point, one which passes through the center point. Or in simpler terms, measure from point A to the points on the circle that are 10.5" away from it.
I did a spot check on the measurements, to check how far each cap point would be from each other around the equilateral triangle, and what do you know -- it's approximately 18" from point to point! Very cool!
I drilled a hole through each 1-1/2" PVC cap (actually off-center and at a slight angle) and screwed them into the board at these points.
So now the tripod legs can seat securely into those caps and a bungee cord down to the center point pretty much fixes the tripod firmly onto the dolly.
And the tripod is perfectly centered on the board!
(The wheels look out of whack, but it's just the camera angle, they're actually nice and straight.)
_________________________
The three holes at the back of the board allow attaching strings. (I have a shot planned where the dolly track will be on a downward incline, so this will allow me to just slowly feed the string out and let the dolly smoothly roll down towards the subject for a close up.)
I still plan to add a couple of handles for easier carrying.
(Now with DIY project #1 done, it's on to the "SteadiCam" stabilizer next!) :cheesy:
