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



## Brian Rupnow (Feb 14, 2011)

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'-------


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## gbritnell (Feb 14, 2011)

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


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## kcmillin (Feb 14, 2011)

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


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## Brian Rupnow (Feb 14, 2011)

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.


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## tel (Feb 14, 2011)

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


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## dsquire (Feb 14, 2011)

Brian Rupnow  said:
			
		

> 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


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## Brian Rupnow (Feb 15, 2011)

tel  said:
			
		

> 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.


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## tel (Feb 15, 2011)

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.


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## maury (Feb 15, 2011)

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


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## bearcar1 (Feb 15, 2011)

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


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## kcmillin (Feb 15, 2011)

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


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## Brian Rupnow (Feb 15, 2011)

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


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## mh121 (Feb 15, 2011)

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


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## Brian Rupnow (Feb 15, 2011)

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----


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## rleete (Feb 15, 2011)

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.


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## rleete (Feb 15, 2011)

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.


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## chuck foster (Feb 15, 2011)

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


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## Brian Rupnow (Feb 15, 2011)

aermotor8  said:
			
		

> 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.


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## Brian Rupnow (Feb 24, 2011)

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.


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## Brian Rupnow (Feb 24, 2011)

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!!!


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## Brian Rupnow (Feb 24, 2011)

Of course, once I get everything removed that I don't need, it becomes obvious why I got it for $5!!!!! Somebody has turned on their wipers with the wiper blades frozen down to the windshield and stripped a spot on the nylon worm gear. Damn!!! However, the worm still engages enough to turn the worm gear---just barely. I have to machine a housing to accomodate both gears, and when I do I will run enough of an interferance that the steel worm will cut a little deeper into the nylon. There won't be nearly as much load as would have been imposed by the electric motor, so it will probably be okay for what I want it to do. Ya just can't trust them greasy buggers at the wreckers--Although in all honesty, I don't think they knew either. That wiper motor has probably been setting around inside the wreckers shop longer than the kids been around who sold it to me.


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## Captain Jerry (Feb 24, 2011)

Hey Brian, I like your rotating hammer idea. You might look into a one way bearing or an over running clutch so that the hammer freewheels on the down stroke. The more I think about it, so what if it unloads the engine on the down side. It will "miss" like its supposed to. Sounds like a good demo cycle to me.

Jerry


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## Brian Rupnow (Feb 24, 2011)

Jerry---Thanks for having a look. I hadn't thought about a total freewheel. Thats a great idea. I'm not sure where I would get one unless I broke out some cash and ordered one from Canadian Bearings. I know that the old bicycles with coaster brakes has a free wheeling rear hub, but thats a bit large for my "scale". I like the concept---the engine works hard when raising the hammer, the hammer goes "over the top" and swings down to bottom and inertia carries it part way back up.--The engine goes into "miss mode" while this is happening, then back into full "hit" when the hammer tries to swing back and the freewheeling clutch kicks in.


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## kcmillin (Feb 24, 2011)

FWIW, if all els fails. I have made a worm gear setup in the past using a homemade regular style gear, and a piece of aluminum threaded 1/2-13. Of course with a lathe you can make whatever thread type you want to fit whatever gear you got. This may not be a "Real" worm gear setup, but it worked flawlessly for me. 

The gear I used was cut using a single point cutter I made to resemble a gear tooth, it was by no means a proper gear cutter. I then used the rotary table and eyballed the first tooth to the closest denominator of 360, and proceeded to cut the rest of the teeth to that degree setting. 

I think if you used a 60 degree single point for the gear teeth, than the screw you cut should fit.

Sorry for the long winded, and possibly irrelevant response. Just thinking out loud.  

Kel


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## Captain Jerry (Feb 24, 2011)

Brian

$6 or $8 US in small sizes from here.

http://www.vxb.com/Merchant2/mercha...ings&Category_Code=One-Way-Bearings&offset=60

Or something like a 1 tooth dog clutch which would be a simple shop project. The weight would swing like a pendulum with the engine in "miss" mode until the single tooth caught up. Might even be better because the viewer could see the operation of the driving tooth. One way bearings might be more mysterious.

Jerry


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## rleete (Feb 24, 2011)

I've ordered from them through ebay. One word of caution, Brian. If you do order from them, be sure to uncheck the box for email "specials". They tend to over do it quite a bit. But decent quality bearings at good prices.


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## Brian Rupnow (Feb 27, 2011)

Well Dang!!! I should have lestened to Aermotor8. Wife and I had weekend guests from out of town, and the fellow wanted to go to Princess Auto to buy something. I went over with him, and took a look in the "Surplus" section. Brand new wiper motor assemblies for $9 and change. I bought one for my new toy.


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## Brian Rupnow (Feb 27, 2011)

Some very interesting findings here. First, the permanent magnets are glued into the motor casing, but readily release when the sides of the motor housing are heated with an acetylene torch. The housing itself is made from mild steel.


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## Brian Rupnow (Feb 27, 2011)

The armature shaft is one straight peice, and the armature itself appears to be made from a stack of metal discs that are attached to the shaft with some kind of epoxy. It cuts easily with a carbide tool in the lathe. The copper commutator is not really attached to the shaft at all. It is held in place by the 2 miles of copper wire that are woven thru the armature discs and soldered to the copper commutator bars. Once the wires are cut away on the lathe, you can pull the copper commutator off the shaft easily.


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## Brian Rupnow (Feb 27, 2011)

Since the motor housing is cylindrical with a flat on each side, the current plan is to make up a peice of aluminum plate that will fit into the peice of motor housing which has the flange on it and center drill it for a .3125 bushing. The shaft is 9mm, but since all my reamers are imperial sizes, I'll turn the end of the shaft down to .321' (5/16") 7.94MM and have enough shaft sticking out of the end of the housing/aluminum plate to mount a pulley on.


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## Brian Rupnow (Feb 27, 2011)

And voila'---A really nifty little 40:1 worm gear reducer. I will probably have to put some kind of collar on the shaft inside the aluminum endplate I will create, because depending on which way I rotate this thing the worm shaft will have a tendecy to "unscrew" itself from the worm gear. This wasn't an issue in its original shape, as there was a peice of nylon acting as a thrust bearing in the end of the motor housing.


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## tel (Feb 28, 2011)

Brian Rupnow  said:
			
		

> 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!!!



 ;D All you hadda do was count the teeth on the wheel - 1 turn of the worm = 1 tooth!


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## Chaffe (Feb 28, 2011)

as long as it is single start worm that is


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## Brian Rupnow (Feb 28, 2011)

Good plan guys, but you can't get at the wheel on this unit. Its sealed.


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## Brian Rupnow (Feb 28, 2011)

So there we have it---a beautifull little gear reducer. And this one is a 60:1 ratio.


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## Brian Rupnow (Feb 28, 2011)

Add a pulley, and we're good to go. Man, that was almost too easy!!! as you probably noticed, i didn't turn the shaft to a smaller diameter. I used the full 9M and bored a peice of brass to 9MM to make the bushing----No reamers involved!!! ;D ;D


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## Brian Rupnow (Feb 28, 2011)

I stand corrected!!! That is not a windshield wiper motor as originally thought. It is a power window motor.---brian


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## kcmillin (Feb 28, 2011)

Brian Rupnow  said:
			
		

> I stand corrected!!! That is not a windshield wiper motor as originally thought. It is a power window motor.---brian



Yep, thats it. Now your gonna have to start over :big: :big:

Kel


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## Brian Rupnow (Mar 1, 2011)

The crankshaft on my engine was just a tad too short to put a pulley on. It stuck out about .28" from the edge of the flywheel, which was enough to get a .093 dowel pin through for my electric start adapter, but no room left for a drive pulley. Today I took a peice of 7/8" dia. 1018 mystery metal and machined a "crankshaft extender". Its bored 3/8" to slide over the end of the crankshaft, and is dowelled in place with a .093 roll pin. The large diameter has a groove cut for on o-ring drive belt, and the other end is turned to 3/8" dia. and cross drilled for the starter roll pin.


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## Brian Rupnow (Mar 2, 2011)

It gets curiouser and curiouser---The machined and split hub has a clamp bolt which locks the hub onto the drive gear. The 5/16" diameter bent rod is pinned into position in the hub. There will be a 1.5" diameter brass ball with a 5/16" hole through it to slide over the rod, and a set screw to lock it in place at various distances out from the center of the hub. once I get the mounting bracket made up, the gear reducer will mount so that the pulley groove in it lines up with the pulley groove in the crankshaft extender that I put on the hit and miss engine. Then when I put an o-ring drive belt on it, and if I'm very very lucky, the brass ball will slowly rotate on the end of the arm. The axis of rotation will be horizontal. that means that when it is swinging from bottom to top, the engine should be "under load" and should fire every cycle. Once the brass ball passes over the 'top" and starts back down, gravity will assist it, taking the load off the engine and hopefully letting it go into "miss" mode. I chose to use a worm gear so that the weight of the ball would not "back drive" the engine as it is on the downswing.


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## Brian Rupnow (Mar 3, 2011)

Here are a couple of (from my point of view) interesting videos of the hit and miss engine under a variable load. It definitly does go in and out of hit and miss mode. However, its not CONSISTENTLY going in and out. Part of the reason for that is that my o-ring drive belt slips a bit, right at the crucial moment when the engine is supposed to be working its hardest to lift the weight. ---in fact, in one of the videos you can see my hand helping the weight "over the hump". Also, the fact that there is considerable tension in the drive belt (o-ring), means that there is some load on the engine all the time which imposes some load even when the weight is in the downswing side of its arc. The engine certainly doesn't lack for power. There are a couple of fixes for this belt slipping issue. I could go to a larger diameter pulley on the engine, which would give a larger contact area with the belt, but the slippage appears to be happening at the pulley on the gear reducer, not the engine. (All pulley systems slip a bit, its just not visible at high speeds). The better solution would be to substitute a pair of light sprockets and a roller chain for the o-ring drive and pulleys. A chain drive has a double advantage---zero slippage, and practically zero tension related drag on the engine. In the middle of one of the videos you can hear the chime that my wife rings to call me up to dinner!!! I have a two way speaker system between my office/test bench and the main floor of the house. The ratio between the engine crankshaft and the output of my worm gear reducer is about 137:1----not because I needed that much torque multiplication, but because I wanted things to happen in a slow enough time sequence that you could see and hear what was happening. As I started my preliminary testing, the first few weights I used were to puny for the engine to even notice that it was under a load. By the time I got to a load heavy enough to make the engine set up and take notice, the o-ring drive belt began to slip. I'm enjoying this, and it is very interesting.---Brian


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## Captain Jerry (Mar 3, 2011)

Brian

If the slipping is occurring at the big pulley, I would bet that the problem is in the belt groove. Probably too wide or too shallow so that belt contact is only at the bottom of the groove. You might try taking just a small shallow v out of the bottom of the groove. 

You may find that the worm mech while preventing back feed to the engine also limits the acceleration and prevents the engine governor for reaching miss kick-out speed as easily.

Another way to reduce belt slippage while reducing belt tension is to put an idler on the slack side of the belt that forces the belt to make contact on a longer arc around the pulley. 

Lots of things to mess with. Have fun!

Jerry


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## Brian Rupnow (Mar 3, 2011)

Jerry--You might very well have something there. The groove in the small pulley (which is not slipping) was plunge cut with a threading tool. The groove in the big pulley (which is slipping) was plunge cut with a cut off tool, and consequently has a flat bottom. That is an easy one to fix. I'll let you know.---Brian


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## tel (Mar 3, 2011)

That might go some way toward fixing the problem, but the rancid truth is that 'O' ring cord is not good belt material. You would be better getting, say, a sewing machine belt - either flat or toothed.


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## Brian Rupnow (Mar 5, 2011)

Captain Jerry--You were right. When I recut the groove in the large pulley so that it has a tapered bottom instead of a flat bottom, that stopped the belt slippage. The problem is that this small engine is too powerfull for this type of mechanism to "display" really well. And the mechanism, while correct in theory, is too damn big and clunky looking. I'm pleased that it works, but I think I will take a closer look at G Britnells suggestion of a Prony brake. Perhaps not a band style brake, but rather a pad style brake with a felt pad, on a peice of spring steel which could be activated by a small handle with a rotating cam. The felt "pad" could possibly bear directly on the outer face of one of the flywheels.(I'm not sure how the bronze would stand up to that). By simply flipping the short handle on the cam thru 90 degrees it would engage and lock the brake in place, imposing a load on the engine to make it 'hit" every cycle, and the amount of pressure would be regulated by the spring steel supporting the pad. Hmmm---I'll have to think on this.----


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## Chaffe (Mar 8, 2011)

very interesting, one question, does the engine hit and miss without the bob weight? i wonder if you could put some sort of hook lifting a weight that then drops it over tdc, free wheels down then picks up another weight? would work with water too i suppose


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