Thread: Help/advice with a coffin thumper

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Hey all, new here... also relatively new to halloween animatronics, although this year I am jumping in head first with a huge plate of stuff I plan to do.

So... here's my question in search of advice...

I want to make a coffin thumper this year... I'm going to build a coffin for my yard, and when activated, I want something inside it to thump the inside of the lid, like something is trapped inside trying to get out by pounding on the inside...

I'm an extremely amateur electronics guy, a moderate electrical guy, and an experienced programmer. So I have a lot of tools at my disposal...

So I had a few ideas - no idea how many are feasable...

The simplest idea I had was a wooden arm attached to a motor... energize motor, arm swings into lid. Thud.

Problem is to get decent power for it I think it'd have to be an AC motor - I'd rather use DC.

Also I'd like to be able to tump thump thump like a fist beating on a door... and that kinda arm wouldnt reset fast enough.

So I thought a piston.

Don't want to use penumatics, as I dont want to deal with the air compressor noise. But I dont know any other type of piston I could use... a solenoid wouldnt have a long enough throw I'd imagine to make a good solid thump.

So, any ideas?

What about the motor idea you originally had but instead of an arm, use a custom designed cam that runs off the motor and has "lands" in it that , when it operates, makes it sound more random than an arm constantly striking at the same times. You could even put a couple of cam discs on the shaft to make it even more random sounding and it wouldn't be that hard to do. Make a wooden disc, circular, then use a jigsaw to shape the disk any way you desire, a bump here, another there and......."voila" instant coffin thumper!!!!

My concern with a cam is that it wont have enough force. I want it to THUD the lid, not tap or bump it...

I'm not worried about randomness of the sound, that I'm controlling via a computer program or other method.

Just trying to think of an affordable way to do it, thats not pneumatic, that can possibly move quickly if necessary. Piston still seems like the best way, but I'm not even sure if there are electric pistons like that thats not a small solenoid...

I would go with the wiper motor







Connect the piston to a non threaded bolt and the piston will slide on the bolt and knock on the coffin . Like the bolt in this picture. You would need to adjust the length till you got a "knock" instead of a push like I have.

Looks good - what is 'the wiper motor'?

Here is an idea:

Take your motor and attach a circular disk to the shaft.

On the shaft attach some lengths of bicycle chain at several points making sure they don't unbalance the motor. (bicycle chain is great because it wont flop around side to side)

At the end of the lengths of chain put some bolts or something with a bit of weight to slam against the coffin door. Maybe even pieces of wood for a bit less damage to the coffin lid.

Here is a quick sketch of this:




The only down side to this design is that your motor must have enough torque to get his disk moving quickly. It isn't instant.... for what you are doing this would be inexpensive and would do the trick. If you are willing to work with solenoids that might be a bit more complicated but if you are willing to do the work with providing pulses at a specific rate you would probably be better off going in that direction.

Originally Posted by lorddamax

Looks good - what is 'the wiper motor'?

A wiper motor is a DC motor that is used to move the wiper blades on a car. You can power one with a car battery, car battery charger, most printer power cords, or a PC power supply.

You can get a motor at monster guts or the local junk yard which will be cheaper and no shipping. I believe the monster gut motor cost $17 plus shipping, new or rebuilt and a junk yard motor usually cost $5 to $10 dollars, used.

I planned to make one this year with what I have going it looks like it will be next year. I was planning on using a cam for this. But the cam would be used to draw back the hammer and a bungee would cause the hammer to strike the coffin lid.

Sounds like a complicated setup - maybe a bit more points of failure than I'm looking for.

I think at this point I'm going to go for a wiper motor that will pump a wooden lever into the lid. Given the variable speed and the DC power I can run it pretty much how I want to... now I just gotta find the parts somewhere. To be honest, I've never been to a junkyard and I'm a bit intimidated! My local one is in a bad part of town, and I'm not a car person... so... I may just use the net

a lot of folks used pneumatic box pusher kits that will make the coffin jump and slam around. The were really cheap on some of the surplus sites. I will check and see if I can find one for you