Making a Hit 'N Miss engine Hit N Miss---

[Brian Rupnow]

Yeah, I know---Screwy sounding thread name. Just thinking out loud here folks. A model hit and miss engine is SO much more effective, if you can show the uninitiated how the engine "hits and misses" when it is in a "no load" situation, but how it buckles right down and hits every time when a load is imposed on the engine. Yeah, I know you can do it with your thumb on the flywheel, but I think thats a bit hokey. I'm thinking off a good weight, something like a chunk of cold rolled about 1 1/2" dia. x 2 1/2" long, attached to an arm, attached to a rotating hub. You would have to put a pretty good gear reduction in there, because we would want the weight to rotate slowly. The gear reducer would be driven off an o-ring drive belt from a small pulley on the engine crankshaft. When it was being lifted through its arc from the bottom to the top, the engine would come under load and should fire every time. Then when it swings "over the top" and starts down the other side of its arc, gravity would take over and all load would be removed from the engine, so it should go into its "hit and miss" cycle untill the weight reaches the bottom of the arc and starts back up again. It wouldn't have to be mounted on an arm as I have shown----Could be a disc. Just thinkin'-------

 

[gbritnell]

Hi Brian,
There is a device called a Prony brake. What it does is put load on the engine, usually driven by a belt from the engine. The brake consists of a band with wood friction blocks attached to a fulcrum which presses down on a scale (weight scale) As the blocks are tightened against the brake flywheel the scale reading are taken in conjunction with the rpm of the flywheel. When the calculations are made the hp. of the engine can be determined.
You could make a lever arm with a wood block attached to it. The movement of the lever arm would be controlled by a screw with a small crank handle attached to it. As you turn the screw the wood block would press lightly against the flywheel adding load and thereby making the engine go into 'hit' mode.
George

 

[kcmillin]

Thats a great Idea Brian. Make you engine work, pretty cool.

I do have one thought though. The weight of the load on the arm when it is on the down side of the revolution might cause the engine to only miss and not hit since there will be energy from the arm getting transfered into rotational energy in the flywheel, I believe it would be like winding a toy car, the farther the weight gets to the bottom of the cycle it would probably speed up as the engines flywheel spins faster.

Just a thought.

Kel

 

[Brian Rupnow]

George---Thanks for the thought. I know about prony brakes, but I was aiming more for something that was more or less self automated. Kel, I've thought about the issue you mention myself, and that is a definite possibility. A perfect solution to that would be a worm drive with greater than a 40:1 ratio, bcause they won't backfeed, but that lays outside my capabilities as a model engineer.

 

[tel]

Yo Brian, your Nodding Donkey oilfield pump should do exactly the same thing as that gizmo.

 

[dsquire]

George---Thanks for the thought. I know about prony brakes, but I was aiming more for something that was more or less self automated. Kel, I've thought about the issue you mention myself, and that is a definite possibility. A perfect solution to that would be a worm drive with greater than a 40:1 ratio, bcause they won't backfeed, but that lays outside my capabilities as a model engineer.

There lies your challenge Brian. Come up with the "greater than a 40:1 ratio" and challenge your "capabilities as a model engineer". :bow:

Cheers

Don

 

[Brian Rupnow]

Yo Brian, your Nodding Donkey oilfield pump should do exactly the same thing as that gizmo.

You are absolutely right Tel.--Its just that the pumpjack I have finished is set up with Elemers#33 on it, and the scale is about right. I don't want to tear it down, and I don't want to build a second pumpjack.

 

[tel]

Fair enough mate. The drive mechanism in the flat bit of a windscreen wiper motor is a worm n wheel with roughly 60:1 reduction.

 

[maury]

Y'all, there is no need to hesitate on a project because of gearing. This site

https://sdp-si.com/eStore/

has worms and worm wheels, and many other types of gearing in a great variety of sizes
at quite low prices.

I too would like to see a project that would demonstrate the hit-miss cycle, it is really about what this method of governing is all about.

maury
www.lonestarengineworks.com

 

[bearcar1]

Hi Brian, I like your idea of showing off the H/M cycle, maybe you could utilize your original idea of placing a load on the engine and then releasing it by means of a pile driver arrangement. A stand-off scale version would be a novel approach and could prove to be fun to design and watch as it does it thing. (desk top rock crusher?) Be a helluva walnut cracker at parties :big: If you could design up a prony brake, now that would be pretty slick as well. Then you could do a hands on demo of the H/M principle while explaining the theory itself. Whatever you come up with will be cool, I'm sure of that.

BC1
Jim

 

[kcmillin]

I think Jim has a great Idea. Some Kind of weight that can be lifted and then dropped, all the while the engine would be controlling a belt of some sort with a hook to grab the weight then release it at the top and the engine would then be missing until the hook found the weight again.

Kel

 

[Brian Rupnow]

I like Tels windshield wiper worm gear reduction---gotta research that one a bit.----Brian

 

[mh121]

Great idea Brian, like someone has already said a windscreen wiper box could yield some useful gearing. I know when I drive the pump I have just made with the R&V engine it hits all the time under load and then goes to h & m mode when running on the loose pulley. It sure shows how hard these little engines can work when they want to, and it sure does run hot when under load !

Cheers
MartinH

 

[Brian Rupnow]

I just called the local auto wreckers and asked the price of a windshield wiper motor/gearbox combination. I was told $35.00 I said that I didn't need the electric motor to be in working condition----still $35.00!!! Sounds a bit steepish to me----

 

[rleete]

That's robbery. I can get new ones for less than that. I think I paid $18 (US) for them last time I bought any.

We use them as the driving force in our "animatronic" Halloween displays.

 

[rleete]

Try here: http://www.sciplus.com/category.cfm/subsection/18

Not sure about problems shipping to Canada. Someone here ought to be able to help you out if that's the case.

 

[chuck foster]

brian there must still be a scrap yard near you, they sell stuff like that by the pound. you go in and remove it your self.

hope this helps

chuck

 

[Brian Rupnow]

brian there must still be a scrap yard near you, they sell stuff like that by the pound. you go in and remove it your self.

hope this helps

chuck

You can't do that here anymore. Insurance regulations won't let you go into a wrecking yard or scrapyard and pull parts.

 

[Brian Rupnow]

Today I was out running all over town looking for hinges for wifeys kitchen renovation project. I had to drive right past an auto wreckers, so I stopped in and asked about wiper motors. I told him that I didn't care if the motor ran or not, and that I didn't care what car it was from. I explained that I built model mechanical devices as a hobby, and all I really wanted was the worm gear and worm shaft and possibly the housing. Bottom line was, I walked out with this for $5 cash. I am busier than a one armed paper hanger right now with "real" work and kitchen renovating, but I think this will work fine for my anti back-drive gear mechanism.

 

[Brian Rupnow]

I just pulled the motor housing off, and by turning the armature and watching the worm gear I have established that the ratio is approximately 42:1---PERFECT!!!