Design weight of 1800 pounds loaded up!
So the good news is that the weight can be moved around and main actuator is holding the weight. The bad news is that, although the weight is evenly distributed about the pivot point, the CG is moving around (something I should have accounted for). Basically as the platform tilts forward more of the weight is ahead of the pivot point and it continues to get worse until it hits the bottom of the piston. And the weight ahead of the CG exceeded the 200 pound capacity of the pistons so we were dead in the water.
I came up with a solution using springs to counteract the effect of the CG moving forward – basically the springs will keep it in a neutrally stable situation where the actuators are responsible strictly for positioning. This should make the calculations simpler as well. In an effort to get a spring load I took our bathroom scale out. The bathroom scale is destroyed but best I can gather is we are looking at 160-190 pounds. The CG will be higher in the completed product so I doubled that capacity with the spring.
Finished the other roll actuator, added a sheet of plywood to the avionics bay to support the weight, and loaded up 1000 pounds of the topsoil this weekend. Haven’t had time to do any motion tests – it sure is scary!
Removed the spacer block from the top of the roll actuator to make up the difference in size of the bottom attachment point. Currently filling the hole with liquid nails held in place with masking tape so that the pilot bit of the bore has something to bite into.
I cut the U-joint and widened the holes slightly where it is now attached to the base of the actuator. Then I used the existing eye bracket by trimming about a quarter inch from the front, back, and top so it fit inside where the spline shaft goes. Only thing now is to find two half-height nuts to reattach the bottom flange but it isn’t going anywhere.
I tested it out and immediately notice a reduction in friction (no force on the linear bearing anymore). There is just enough room for the actuator to move around without hitting the deck of the trailer.
Saw it at 12:01 this morning with my dad in IMAX 3D. Quite a ride! The sets and special effects were everything I expected. The acting was great. The music start out great but ended on a good note (pun intended). The story was good… it has a couple of holes that could probably be explained away but for the masses it will be a head-scratcher. Definitely a prequel to Alien, no doubt about it… but we are on LV-223 (if you missed it) not LV-426.
Stopped at the salvage yard on the way home. They wanted $35 on average for a spring/strut assembly and wouldn’t sell the spring separately even if I had the right tool (which I didn’t). They also only had one of the U-joints that I liked so I ended up having to buy something different.
A few notable changes in the software between day 5 and today:
Dynamic control limit for joystick (0-20 degrees)
Calculating and logging acceleration rate
Clamping rate desired and rate differential
Heave is now enabled again
Configurable frame time
Two additional event buttons
Fixed counter for 10 second min/max calculations
Fixed min/max calculation (not resetting pit/rol rates)
pitlimit was NAN
The latency can be visualized as a phase shift in the attached Excel chart.
I have a couple of theories to try for day 7 tests. First, the static friction value should only be used initially if the current voltage above trim is less than the dynamic friction value. Therefore we must also declare a dynamic friction value (in degrees per second).
Second, I think we should try effecting a change on the system and then waiting 0.3 seconds for the results (EDIT: verified this was already the case).
Finally I wanted to investigate the desired rate calculation… is 60°/s really necessary to adjust 20°?
To speed things up I am also initializing the values for all the sliders to the most recent successful numbers.
Home Depot dropped the price from $1.25 to $0.98 per 40 pound bag. I picked up 50 yesterday (1 ton) to eventually load-test the platform.