Steadicam Prototype v3 Test
I think I’m making some progress! Here is some video I shot of the steadicam prototype arm curling some weights. There are still some obvious problems, but at least it’s encouraging.
3A style topstage
Starting to think about the other parts of the steadicam, working on a 3A style top stage, here’s what I have so far. I worked off some photos I found online, so the dimensions are a total guess. I found a rack and pinion gearset on mcmaster carr, the rest should be pretty straighforward. Going to glue the rack in the top plate, and add some screws to add friction to the sliding parts, as well as some hard stops to make sure the camera doesn’t fall off.
Changes changes
Did some thinking, and I’ve made several changes to the cam/ride mechanism which should help with the issues I’ve been having.
1) made the bottom of the lift assembly thicker so it will have less chance to twist on it’s bearings. I may at some point change this further to grip the post tighter- right now it’s just a set screw, but it might need to be a clamp instead.
2) the ride mechanism gets new larger bearings and shafts- going from 1/4″ to 3/8″ should help with the twisting.
3) I moved the lift adjust screw to the side so the pivot for the ride mech. can be closer to the post, meaning a shorter moment on the twisting action
4) see #2- did the same thing on the bone side of the ride mechanism.
5) changed the cam, now it’s a single piece with a 3/8″ post sticking out.
Hopefully these changes will help.
Design + Development = wow, I respect engineers even more now.
I added a second cam and connecting rod to my arm yesterday. It definitely solved the twisting problem. In the long run, I’d rather just have a single cam, because adding the mechanism to adjust the offset from the cam will be twice as difficult with 2 cams. For now, twin cams, fixed connecting rod length.
The most obvious problem right now is that as the cam switches from pushing UPwards on the connecting rod, to pushing DOWNwards on the connecting rod, the whole assembly clicks and jumps a bit.
I’m also getting way too much friction in all the little rods and bearing surfaces, part from the design, and part from my lack of holding tight tolerances in the machining process. This friction is so great that the arm is sluggish, and I doubt would do much stabilizing in use.
Prototypes are frustrating
I finally completed a prototype of my Steadicam G-series style arm. Yippie!
The bad news is that there are some pretty severe design flaws in my plans. Not sure how the G-series arms cope with this issue- that the cam at the top is pushing only on one side of the top of the spring attachment mechanism… makes the whole thing torqued sideways, as you can see in the top view. Going to try to add a matching cam and rod to the other side to compensate. I’m starting to see how things get over-engineered.
FEA follys
Turns out the FEA I’ve been doing with Solidworks 2007 was based on some mis-information. I was using Cosmos Express (the simple/beginner’s FEA tool in SW2007) and once I realized that I needed some sort of saftey factor on my parts, suddenly I couldn’t make anything strong enough to hold the 300lbs that the spring would be pulling inside each arm segment. I decided to look at some different materials than 6061-T6, and that’s when I found that SW’s material library had the yield strength of 6061 @ 8000psi. Wikipedia and ALCOA list it as a yeild strength of “over 35,000PSI” (http://en.wikipedia.org/wiki/6061_aluminum) which is quite a big difference! Now that I made that change in SW, suddenly all my parts are more than strong enough.
I also re-designed my spring holding apparatus- I’m running 5 steel springs of a smaller diameter to get enough range of motion, and hold enough weight. The upside is that I can also run 4 if I find that it’s way too strong for my camera, or I can run just 1 for very light weights.
Home Built Steadicam
I lurked on HBS (homebuiltstabilizers.com) for years before getting up the gumption to try my own build. Now nearly 6 months later, I’m still planning things out. I’ve reverse engineered the Steadicam G50 arm, and am going to try that as my first shot. Why not eh?! If it works, I’ll be stoked. What’s more likely, is that I’ll learn a lot about machining, and use those skills to make some simpler items.
Here is one of my CAD drawings of the G50 arm mechanism. If I understand it correctly, (from reading the patent) I think that the red parts work as a cam to reduce the spring force as the arm booms to it’s maximum height- which makes certain the arm doesn’t lock up, or bump at the top. At the same time, it also lessens the force of the spring at the bottom of the motion- I’m not sure why this is, and might try to make a prototype to figure it out.