New here, amateur, looking for guidance...

[lorddamax]

First, let me apologize if I'm on the totally wrong forums... I've searched for amateur robotics forums and didnt see much, so I took out 'amateur' and found these forums... if theres a better place for me, I'd love to hear about it.

That being said - I'm a real amateur... I've messed with some electronics, I have some electrical experience, and I'm a programmer. I have the foundation, and the smarts for this, just not the specifics.

My situation: I'm building some halloween animatronics. One item I'm looking to make is a coffin, thats motion-sensor activated (that part I have down - I have the motion sensor that will activate the circuit, not worried about that part), that 'pounds' on the inside of the coffin... al la a zombie trying to get out.

My question: What would be the easiest way to do that? I've had a few ideas... I could set up a wooden lever on a motor that swings into the lid... thud... I was thinking of a piston that rams into it, though I don't want to use pneumatics... I have an air compressor but it's LOUD and dont want it running in my home to power it. I had a few other ideas as well, but wanted some guidance on what may be the best (and cheapest/easiest way for an amateur)
to thump the inside of a wooden coffin lid, relatively hard (hard enough to emulate a fist banging on a closed door for example).

My resources are limited, and I want to keep it simple... a motor attached to a stick that when energized swings into the lid, then it de-energizes and gravity makes it fall down again is what I'm leaning towards first... just need to get a strong enough motor, hopefully DC powered... but if not I can do AC. I'd LIKE it to be able to go quickly, like a thump thump thump... which I dont think powering/unpowering a motor could do quick enough - but thats not the end of the world.

So, any thoughts or guidance?

[Soeren]

Hi,

I think that wood on wood may sound a bit to sharp, but if you wrap the wood (which has to have some size) with some layers of cloth, a thin layer of neoprene rubber, or even some inner tube, it will sound more like the real thing (assuming zombies knocks like pre-zombies.

To get a more speady repeat, use a large(-ish) solenoide (surplus stores or DIY).

[waltr]

Looks like this forum is a match for your skills and ideas. Do some browsing and searching in these forums for ideas and solutions and don't miss the SoR tutorials and articles with lots of more good stuff.

Another forum for you is on the SparkFun web site. I believe a few other people posted there were working on the some halloween animatronics.

Just some ideas:
For thumping maybe a cam on a motor (geared) to move the 'fist'.
A gear motor and a drum that winds up a cable should work to open a coffin door. Then a clutch to disengage the motor to allow the door to slam shut.

[blackbeard]

well you've absolutely come to the right forum! you'll find that this is probably the best forum around on robotics and maybe even electronics as well! as for what you've described it's definitely not impossible and depending on your budget can be made very easily. the one thing that will almost certainly be the most expensive is the motor or actuator that opens the coffin lid. this in my opinion can be solved if you carve the lid out of something light like those insulation foam panels you can get at the hardware store. if you use the light lid like i mentioned and it opens horizontaly with the coffin standing almost in a standing or leaning position then a high torque hobby servo might cut it. otherwise you may need to use something a little stronger like one of those $15 30rpm gear motors i see on ebay all the time. for that however you will need a an H bridge and a tougher power supply as well but both should be reasonably inexpensive. now for the light sensor there are some pretty simple circuits you could do. one would be to use a photoresistor and a cheep dollar store laser pointer. a laser pointer will provide a very constant light level to a photo resistor and when broken that light level is unlikely to be matched by nearby light sources. the only thing with that is that you need it to be perfectly aligned in a spot where someone might break the beam but even this isn`t hard. the last thing you need is a microcontroler. these are also inexpensive and the one in the 50 dollar robot tutorial on the main page is a very inexpensive one at that! another one is the arduino which is a very common one that is very easy to use and very versitile. you can find many programs that you can piece together for this kind of effect. good luck on your build!

[lorddamax]

I think blackbeard missed my point - I'm not OPENING the lid, I'm pounding on it from the inside

What are the SoR tutorials? Remember, I'm new, I dont know the terminology yet

I'm thinking a solenoid may be my best bet, but I'd need a big one. In another forum someone suggested using a windshield wiper motor and attaching a rod to the cam... that may work...

I'm just trying to find the easiest/cheapest way to do it

[Soeren]

Hi,

What are the SoR tutorials? Remember, I'm new, I dont know the terminology yet

SoR = Society of Robots = this site
Tutorials, look at the links on the top of the page.

I'm thinking a solenoid may be my best bet, but I'd need a big one. [...]
I'm just trying to find the easiest/cheapest way to do it

Just shop around, there's plenty to find. Some cheap, some less cheap, but don't overdo the power you need, or the lid of the coffin will be smashed in a short time and a scary bit of wood will emerge 

[lorddamax]

I've been doing a LOT of looking today, and cant find a single solenoid thats larger than an inch or so They are all for really small appications...

Anyone have a link to plans to build, or hints as to how to build, a larger solenoid? I know the principals of it (making the electromagnet) but how to thrust the cylinder out... thats where I'm lost.

 

[lorddamax]

Embarassed... I just googled it again and came across this website's tutorials.

Ok, forgive my ignorance and that bonehead move

And then I read that tutorial, and it just says what it IS, not how to build an effective one. Search continues...

[waltr]

You may be surprised at what a 1 inch solenoid can do. Take a 12 inch long level, hinge (pivot) one end and arraign it so the other end can hit to coffin lid. How far does that end need to move to bang on the coffin? about 3-4inch? So attach the solenoid about 3-4 inch from the hinged end and now its 1 inch of throw will move the hitting end of the level 3-4 inch.

You might also want to google 'simple machines' to get some ideas from levels, cams, wheels, etc.

[Soeren]

Hi,

I've been doing a LOT of looking today, and cant find a single solenoid thats larger than an inch or so They are all for really small appications...

First link, second down in the middle column:

DELTROL 12VDC CONTINUOUS HEAVY DUTY SOLENOID
Deltrol PS75 51073-81 heavy duty 12VDC solenoid. When the plunger is fully engaged it activates a micro switch. Overall size 3-1/2"L x 1-1/2" x 2". Brand new inventory. For full spec consult with Deltrol. $19.95 Ea. 1 in stock MD427"

Another possible source is the an auto wrecker. Solenoids are used eg. to pop the trunk in some cars, not to mention the starter solenoid, which, as it stands, is way too heavy duty for your purpose (but a large hammer can be used for small nails too).

Anyone have a link to plans to build, or hints as to how to build, a larger solenoid? I know the principals of it (making the electromagnet) but how to thrust the cylinder out... thats where I'm lost.

Some of the really large ones are made of plates like a transformer and just pulls the anchor tight to the flat end when energized.
If you unwind an E-I style transformer that isn't welded in the core, you may reuse the E-parts of the core for the magnet and the I-parts for the anchor if you're handy. Save the magnet wire from the low voltage side for the electromagnet.

Another way you could make a solenoid is by using a plastic tube with a soft iron core that glides through it without friction (but still filling it out more or less). Adding neodymium magnets to the core will make it more power-full.
Two discs on or near the ends of the tube will help making a good coil - go with a relatively heavy wire or wind it bifilar.

I'd visit a car wreckers place first.

[Jash shah]

hey plz can any one give me some tips to build my first robot...and i want to build some good bot..if any body have links ..so plz send me...

[lorddamax]

hey plz can any one give me some tips to build my first robot...and i want to build some good bot..if any body have links ..so plz send me...

Excellent location for your post.

[Soeren]

hey plz can any one give me some tips to build my first robot...and i want to build some good bot..if any body have links ..so plz send me...

Google!

Please start your own topic (when you have done a bit of work on your own).