I have a Halloween prop that I made and has served me faithfully for a few years. It is currently controlled by a PIC18. I am switching to AVR and upgrading my mechanics in preparation for the upcoming festivities at the end of Oct. Here is a description of my current rig:
It is a full size automated guillotine.
The main motor operates a pulley via a 'V' belt to another pulley that is connected to a bait caster fishing reel.
When the motor runs, the pulleys turn the reel which is connected to a strong nylon cord that through a couple pulleys, lift the blade to the top. The motor stops when the top is reached. The action of the reel holds the blade up.
When it is time for the super cool head slicing action; another motor with a 'hammer' connected to it, spins and hits the cast button on the reel and the blade slides down.
The victims head plops down, exposing goo, cool sounds, strobe lights, etc.
Another motor repositions head, and everything resets.
Although my fishing reel solution was the only one I could come up with in my original short design time frame, and actually works well, I am unhappy with it.
I would prefer something like an electric PTO clutch or similar to the clutch on an air conditioning compressor. I also thought about fabricating a type of cog and lever/ratchet; it would add an eccentric sound as the lever hit the cogs as the blade was raised. Then using a servo to lift the lever when it was time to lower the blade (using the spindle from a lawnmower pull starter to allow the reverse free fall action).
The blade weighs ~4lbs and the main motor is out of a run of the mill 120VAC 20" box fan.
The actual question:
Does anyone have any ideas for a new lift/release mechanism? I would appreciate it. I have not come across anything that looks like a viable solution as of yet.
Assume that the cord is wound up onto a drum. One end of the drum has 2 (or more) holes that fit matching pins on a wheel on the same shaft. The drum (or the wheel) can slide sideways on the shaft and is pushed towards the wheel by a suitable spring. The motor drives the wheel to wind up the load. For release something (perhaps a servo) pushes the drum away from the wheel (against the spring) so that the pins disengage and the load falls. ???
That is the basis for the inner workings of some fishing reels like the one I'm using, albeit a smaller version. I like mixing mechanical contraptions I have to fabricate into my little projects.
I may build a prototype of what you describe. I have been modding old transformers today to turn them into electromagnets for testing as a release mechanism. Wouldn't be too hard to turn them into some solenoids that connect the 'pins' of the drive wheel to the drum pulling the line.
As of right now the blade falls very good under its own weight. I just have to be careful that any contraptions are lightweight enough to not counter the mass of the blade. Just so I would not have to add weight to the blade, then motor power would increase, etc....
Thanks for your idea. I have the time, motivation and general know how but I fall short of intuitiveness from time to time.
You could use a simple winch servo.
The cord winds up onto the drum then with a second servo you rotate the whole thing so the cord falls off the edge of the drum. Rinse, repeat.
Mount the drum so its axis is vertical (i.e. so the cord will fall off) and then run the cord through an eyelet (perhaps with a pulley) which is normally at the side of the drum (so the cord will wind correctly). The eyelet is connected to the second servo which can drop it below the drum when the cord is to be released. I think the cord would fall off the drum more cleanly than if the drum is moved from horizontal to vertical.
...R
piratebrian:
You could use a simple winch servo.
The cord winds up onto the drum then with a second servo you rotate the whole thing so the cord falls off the edge of the drum. Rinse, repeat.
I believe I will have to continue and design/develop something myself.
Prior to posting, I had not only searched many search providers but browsed, bugged all hardware, motor, electric shops I could find. As possibilities are endless and many times hidden from plain sight, especially for specialty applications; something may still pop up. So far, most are either small and puny or large and bulky. Ones that seem just right are outlandishly priced (probably not so for their intended market/application). I have forgot to check the local junk yards, may give that a go this weekend.
I am going to start prototyping the following three this weekend:
Combination of Robin's ideas
A ratchet mechanism (used in everything from clocks to trailer winches)
Change drive system to lawnmower starter with bendix that will actuate gear connected to drum. Blade held up by electro magnet.
Still hoping a magic plug and play solution will present itself.
Although I have never had the courage to buy anything on ebay, I found a type of electronic clutch I have been looking at for a pretty low price. I'll throw a couple of bids at it (I currently have it at $11.00).
drobe011:
Although I have never had the courage to buy anything on ebay, I found a type of electronic clutch I have been looking at for a pretty low price. I'll throw a couple of bids at it (I currently have it at $11.00).
I will still move ahead as per post above in the mean time.
-Dave
Interesting. There seems to be no mention of the voltage and current requirements for that clutch, nor if AC or DC. If you win how will you attempt to deal with that unknown?
It is a standard electronic clutch for a riding lawntractor.
Cross referencing this part number to the OEM part number, which gives the lawntractor model it goes to, which gives the manual.
Or short, most modern residential riders are 12VDC systems nowadays. Pretty easy test to determine current it will draw. (The total charging system is 16A on the tractor).
Also helps that before my current career I was a licensed Wheelhorse, Toro, Yanmar mechanic.
It may not be usable/desirable, but as I am a hoarder of things; if I do get the bid and it at least works upon arrival, it will give me a little confidence in ebay and be useful in a future contraption if not used now.
Just to give you an idea of what that thing is used for above:
My current rider, you have to pull a lever to engage the blades in the deck (basically applies tension to a 'V' belt that links the motor shaft pulley to the main deck pulley). More classy/expensive riders do this at the flip of a switch through an electric clutch. They are usually pretty costly.
Another approach is to use friction drive to the edge of the drum - perhaps a piece of rubber tube over a
bare motor spindle would do. A solenoid/servo engages to press the motor spindle against the edge of the
drum, motor turns to life load, and release solenoid to drop. A small DC gear motor might be enough
since the friction drive is already a step-down gear. You could even share supply to the motor and solenoid
like in a car starter-motor...
That is a pretty good idea. Probably the simplest to fabricate of my current options. I like simple. An elcheapo or used throw out bearing and throw out arm may be a good coupling/decoupling device.
I actually just got back from walking up and down the isles of my town hardware store looking for misc pieces for the fabs. Almost picked up a clutch for a weedeater, but I figured if I spun it fast enough for that to actuate I would probably launch the blade out the top of my contraption. The blade only has to travel ~5-6 feet to the top.
-Canned the reel and some intermediate pulleys
-Changed to a smaller pulley on motor (used as drum instead of to drive a belt)
-Hooked power up to different winding on motor that allowed more torque
-Electromagnet holds blade in up position
-Blade heavy enough to overcome intrinsic motor/pulley friction to come down with a good thump
Thanks for all the suggestions. With what I had available, I could not get anything built that was lightweight enough. Turned out better in the long run; a simpler system.
Thanks again,
-Dave
Oh, If I do win the electric clutch ebay thing and it ends up being the right shaft diameter for my rider; push button blade operation here I come...
