Saturday, 26 September 2009

Assembling the real thing

Today I started to put the rest of the wood together to form the coffin plinth. I fitted the skeleton raising hardware and realised that the force required to lift the skeleton was warping the back panel of the plinth so I added some reinforcing struts.

Here's a pic of the plinth with the lifter bar raised.



And a close up of the lifter bar mounting. The two pieces of wood next to the lifter bar screw into the sheet of wood that covers the innards of the plinth. The helps to further reduce the torsion on the back panel of the plinth.



I also fitted the coffin lid and the lid lifting mechanism. Here the skeleton lifting bar is in the down position with 'Albert' attached.



Here's a video of it working:




video

Busy week

I've been busy. I've spent the last few evenings assembling the electronics that will enable me to control all the pneumatics from a PC. I've made two mistakes on the board design:

1) The linear regulator holes were too small. It was a simple job to drill them out to the right size but this removes the through hole plating, the result of which is that I've had to solder the pins top and bottom.

2) I got the pad spacing of the 25 way D type connector I was going to connect to the PC with completely wrong. So wrong that the conenctor I wanted to use will not fit in the holes. Fortuanately I had some 25 way cable lying around (as one does) and I've soldered this cable directly to the board and put a connector on the other end to plug into the pc.

Here's a pic:

Sunday, 20 September 2009

Coffin time

Got some 9mm plywood yesterday and started on building 'the coffin'

Thursday, 17 September 2009

Fast boat from China

The printed circuit boards I had made arrived today. They are good quality and four turned up when I only paid for one! Not bad considering I only placed the order on the 4th Sept. and they have been made in and shipped from China!

This sometimes happens when they have a big space on the PCB blanks that they use. It is cheaper for them to fill as much space as possible and so if they have a small design (like mine) that can fill the gaps with they will use it repeatedly.

Good news for me as the boards work out at £11.50 each. Can't argue with that.
Trouble is though, I seem to have got the silk screen over the pads on one of the surface mount footprints. Ah well.



Now where's that soldering iron?

Saturday, 12 September 2009

Raising the dead

I've had to abandon my plan for skeleton raising as detailed in my last post. The forces required are just too high. The problem is that with the lift bar flat, the force required to get it moving is considerable. My piston can just about supply this, but once the lift bar starts to move, the force required to elevate it decreases as it rises from the horizontal. As I cannot reduce the cylinder pressure once the bar is moving then this extra force results in acceleration, the outcome of which is I've made a siege engine.

Here's my test rig with the full length lifting bar installed:


I've only dared to run it once, which resulted in plan B. This involves having the pneumatic cyclinder at 45 degrees ish to the lift bar. This means that the skeleton coffin will have to be on a plinth to accommodate the cylinder. Not a problem.

Here's a video of plan B with the recently arrived 'Albert'

Note the slightly bemused Matthew in the background.



video

I was pleased with the damping effect as the system returns to the start position. I have some 'connectors' that limit airflow in one direction only. The system returns to the start position under gravity and the damping effect is caused by a build up of pressure within the cylinder as the piston compresses the air within it.

Tuesday, 8 September 2009

(Almost) Raising the dead

Finally the rod clevis for the end of the skeleton raising cylinder arrived today:




Here it is attached to the cylinder complete with foot clevis at the RHS and plates to mount to the lifting bar at the LHS.




Here is a highly technical plan of what I'm trying to do.




After a test run my rig failed to lift anything, then almost destroyed itself as I increased the pressure. Due to the short distance between the hinge and the piston attach point then once it got going the unhinged end of the lift bar went too fast.

I am going to have to maximise the angle between the cylinder and the base plate as the piston attaches to the bar quite low so a large force is required to make it move. Maximising this angle helps to reduce the force required to get it started.

Wednesday, 2 September 2009

Still waiting..but some progress

I'm still waiting for a 'rod clevis' to go on the end of my 250mm cylinder which will enable me to test the skeleton lifting mechanics. Ironically the website 'instockdirect.com' informed me they no longer stocked such an item 2 weeks after I ordered it.

Whilst waiting I designed the PCB for the parallel port interface. Here it is:




I originally intended to manufacture it myself but I found someone to make it for me in China for £46 delivered. Bargain!