2020’s Signature Halloween Trail Prop

Update: Just wanted to give a quick shout out to Creepy Joe for giving me the new soundtrack for my clown props (link here). Maybe I’ll add an animation of a clown sniffing a girls hair (link here, here and here) – if that doesn’t give my haunted trail (link here) guests nightmares I don’t know what will!

I can’t believe we are in June already and the date of our Halloween Haunted Trail of Tears is FAST approaching. Worse yet, I am still trying to get the Halloween project posts out from last year. Whoever told me I was going to have more free time when I retired clearly didn’t know how hectic things are around Intrigued headquarters. I am shocked I found time to even have a day job ha! To chip away at the backlog, figured I would go ahead and finish off the second part of the Foam Coffin project – specifically the animation for last year’s signature piece. If you recall, the first part of this project was making the coffin (link here).

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

That was actually supposed to be the easier part of the project, but putting all the extra design time in to create the foam board connector system and making the foam cutter (link here) added a serious chunk of time. Luckily, I had started work on the animation at the beginning of the year or there would have been zero chance of this prop making it to the trail last year. Actually it started midway through the previous year when I was working on the Servo Man two servo mechanism (link here), but I will get to that after I talk about the concept.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

Hit the jump to read how a spooky concept came to life!

The reason I needed a coffin is I wanted a new animated prop for the graveyard. That area has been building up over the years and now had a good smattering of animated props from the Nightwings (link here) to the Grabbers (link here and here). The graveyard is a large feature on the trail and it was time to take it up a level. After some noodling and looking online for examples, came up with the idea of having skeletons digging up a coffin and then opening the lid to reveal the decaying body inside – maybe even have it raise out of the coffin once the lid was opened.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

So, finally had the concept and now just needed to make it happen. Anyone that has done any project of relative complexity is fully aware that coming up with the idea is a helluva lot easier than bringing it to life – not to mention all of the design changes that are made along the way, some for the better, some because paper doesn’t always reflect real life (that trickster physics seems to always get in the way). I mentioned in the foam cutter post that I originally wanted the coffin to look like it was being pulled from the ground (half buried). That transformed into the full coffin now that I had the foam cutter jig (a change for the better). I still needed to have a way to stand it up.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

That ended up being an easy one to solve. I didn’t want to put a lot of stress on the foam and wanted to have good support for the figure inside to push against. Screwed two pieces of PVC board together sandwiching the foam on the bottom panel (there is a matching board inside). Added two 1″ PVC end caps to the bottom and then two 45 degree couplers to hold the support pipes. This gave a perfect angle for the coffin and was extremely sturdy (legs also came apart quite easily for storage).

Okay, now on to the inner coffin animation. With Ron’s help we figured out that a single pass through axle servo could be used to raise the body out of the coffin. I had picked up several of the stronger 7.2V LIPO servos early on knowing that the standard ones I was using would struggle with lifting long arms with weights on the end. Printed up a coupler that would screw into the rotating servo plate and hold 3/4″ PVC pipe. Here was our test harness so we could test the movement and figure out how much torque it had.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

It ended up not have enough torque to lift a really heavy body (there’s that physics again). Rummaging through my Halloween bins we found a smaller skeleton that had nice articulation joints and surprisingly fit the size of the coffin (the smaller size also gave it an unexpected creepier feel). It took us some time to figure out the mechanics of how we wanted to hook it to the servo and then exactly what movement worked with the opening lid.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

A slight design change occurred here. We wanted the coffin top to slide off as it was pulled by the other skeletons. Due to the range of motion that was available to do that (more on that in a bit), we knew that it was best to minimize the opening to just enough to allow the skeleton to pop out. This meant we had to push the pivot point to the far side and then turned the skeleton so it would come out sideways.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

Like the coffin support, we used two pieces of PVC board (one inside and one on the back) to create a platform for the pivot point. This time we used an end cap and a 90 degree coupler along with the 3D printed coupler and servo (I designed the couplers to both hold the base of the servo and to couple the part to move). You can see the skeleton positioned above and then how it moves out of the coffin when it is opened below.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

Did I mention all this work was being done a mere two weekends before the party! Can’t thank Ron enough for coming down and helping me get this thing together – we got very little sleep that weekend and if you see us in a picture, assume we are completely exhausted. During our testing we realized that the lid had a lot of friction as it moved off from the grit in the paint. It felt/sounded like sandpaper grinding as it moved past. Although a spooky effect, not efficient for what we were trying to do. Rummaged through the backroom and found some extra supports for wire shelving that we originally used in our bedroom closets. Replaced those with wood units and had these left over. Cut them to fit across the bottom and then on the upper left side (see picture above). Slapped some wooden dowels on the end and used the foam connector holes to hold it into place (double duty as they also held the sides together). Now the lid could slide easily and from right to left.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

Okay, now for the last part. Unfortunately, in the heat of the moment to get this done in time I didn’t have a lot of time to take many in process shots. To give you an idea of how close this came to missing the trail, we had to get it functioning a few hours before the event started – that rush also caused me to make a serious design error that we didn’t find out until we went to move it out of my den.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

I need to talk through the shot above as it represents months and months of work. First the servos that make up the arm. I had spent most of the year working on a 4 axis arm that was capable of replicating any movement of the human arm. That meant a servo for the shoulder, bicep, elbow and an elbow twist that allowed me to rotate the wrist. I must have studied my own arm movements for 2 solid months to figure out how to mimic our incredibly complex and flexible structures with servos and PVC pipe. Figured it out and then created an Arduino sketch that allowed me to move each servo independently for detail positioning and then in the end move all the servos in an interlaced fashion to mimic whatever movement I wanted (throwing a ball, shaking hands, lifting something etc.). This would give me full flexibility when I went to construct the planned coffin prop. Turns out I didn’t need all that complexity for this prop – still incredibly nice to have for future projects! Technically I only needed two movements, the shoulder and the elbow. Rebuilt the arm with just those two pivot points and then connected them up to my large skeleton. I will clean up the frame for this year, but in the limited time we had, we just fit the PVC frame into and around the skeleton as needed. It definitely took some trial and error to get the movement we wanted replicated so it could open the lid smoothly. As physics came into play again, we had to overcome the extra effort to get the lid moving from rest and then be able to push it back along the right plane. We hooked the hand to the top of the coffin and then attached the forearm with a spring to the underside of the lid. This damped the initial jerkiness of the pull.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

Then it was just a matter of getting the timings right in the program. Trigger the two servos on the external skeleton to open the door, move the servo to pop the small skeleton out of the coffin, after a bit, pop the servo to bring the small skeleton back in and then reverse the external skeleton servos. Forgot to mention, there is a dowel rod in the lower left corner that the lid rotates on. Oh, and the orange power cord was temporarily draped over the skeleton to get it out of a pool of water it was sitting in thanks to the nonstop rain we were getting (had to put all the controllers in the Tupperware container you see in order to keep them dry as well).

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

The angle above is the direction our guests would be viewing it. There was supposed to be a flag in the little skeleton’s raised hand that announced my retirement, but we didn’t have time to get that made. I did notice the upper arm wasn’t attached to the pipe and got that fixed before the guests came.

Project Foam Coffin Halloween Project for Haunted Trail of Tears 2020

Couple of things to mention that will be fixed for this year. First of all, I didn’t get a chance to add in the rechargeable LIPO batteries to power everything. Those things can be a bit scary to the point they can blow up if you don’t treat them right. Taking that concern to heart, we simply used my configurable power supply and dialed in the 7.2 volts and current they needed. Hated having my expensive power supply out in the rain, but it turned out okay. The other thing is the design screw up. I hard wired all the servos in – all of them – the two in the exterior skeleton and the one inside the coffin. If you think through more than I did you would have realized that doing that meant that both pieces (the coffin and the external skeleton) has to be moved together. Now that was a pain in the ass and a good example of what happens when you are completely exhausted and not thinking right in the heat of the moment.

Okay, now for the video!!!

All our guests really liked it and admittedly pretty proud of what Ron and I were able to come up with in a relatively short period of time. It will undergo some definitely improvements for this year and will be a signature piece for years to come. I owe Ron a lot on this one – hell, a lot in the overall event as he is my sounding board for ideas, mentor on all things electronics and physics and spends countless hours helping me set up and tear down every year.

Can’t wait to see what we are able to bring to the trail this year – especially now that I am officially retired.

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