My Tractor Forum banner

1 - 20 of 27 Posts

·
Registered
Joined
·
210 Posts
Discussion Starter · #1 ·
I'm trying to think up a way for a Rev Limiter on a lawnmower engine. I know it seems useless for those of you that still have hand controls. but if you have a foot throttle it could be useful for those agrivating times where you get a lead foot and decide to hold the throttle wide open for about 30 seconds... right now my idea is like the throttle control on most push lawnmowers, with the little "flap" inside the shroud that catches the air off the flywheel and regulates the throttle. Well, my idea is to have one of those, and have a little switch wired for a 'secondary' kill wire it pushes when you get to whatever rpm you have it adjusted to 'activate' the switch at. Thoughts? critisism? people telling me to stop bein an idiot and get back to mowing?

:greendr:
 

·
Registered
Joined
·
1,016 Posts
Shouldn't the governor regulate it to a safe RPM at all times????
 

·
Registered
Joined
·
210 Posts
Discussion Starter · #3 ·
Shouldn't the governor regulate it to a safe RPM at all times????
well yes, but if you have a foot throttle set up like I do, then no. I bypassed mine because the max RPM's the governor allowed weren't quite enough for what I do.
 

·
Registered
Joined
·
123 Posts
I would do it electronically. The existing ignition is electronic so just add to a limit for the RPM to a quantity that you wish and shut the ignition off. When the RPMs drop to a safe point, turn it back on.

You would need a Hall sensor to count RPM's from the magnet on the flywheel. A definite period refreshing counter with a high count on and low count off so that when the RPMs reach a high - shut the system down until it reached an RPM low that switches it back on.

The whole system could be programmed into a Programmable Integrated Circuit chip that would do all of the counting and switching. There are PIC chips with ample power to do the task. The existing module would be under the PIC chip's control through either relays or MOSFET's. MOSFETs are more reliable...

It would be an exercise in smashing the brain against a problem and learning a massive amount at the same time. There is plenty of info either on-line or text to steer you through. You can probably do this just fine - not as complex as you may think.

Bill C.
 

·
Registered
Joined
·
210 Posts
Discussion Starter · #5 · (Edited)
I would do it electronically. The existing ignition is electronic so just add to a limit for the RPM to a quantity that you wish and shut the ignition off. When the RPMs drop to a safe point, turn it back on.

You would need a Hall sensor to count RPM's from the magnet on the flywheel. A definite period refreshing counter with a high count on and low count off so that when the RPMs reach a high - shut the system down until it reached an RPM low that switches it back on.

The whole system could be programmed into a Programmable Integrated Circuit chip that would do all of the counting and switching. There are PIC chips with ample power to do the task. The existing module would be under the PIC chip's control through either relays or MOSFET's. MOSFETs are more reliable...

It would be an exercise in smashing the brain against a problem and learning a massive amount at the same time. There is plenty of info either on-line or text to steer you through. You can probably do this just fine - not as complex as you may think.

Bill C.
I like that idea. my main problems right this moment is I'm broke. just figured I would post here and get some gears turnin in peoples heads. Thank you alot.

First I need to find a way to moniter my RPM's. then I guess I can go from there. Any ideas on a *cheap* way to do that?
 

·
Registered
Joined
·
248 Posts
We use a throttle stop, adjustable at the carburetor and/or the pedal, with a stop screw. We have a digital tachometer (available at Northern Tool for $30) that we use to set our limit at 4000 rpm. We block the travel on the pedal, to stop the throttle at the desired rpm...so not a lot of pressure is placed on the cable and carb linkage.

MSD makes a digital limiting ignition control box, that limits the rpm electronically (p/n 4217, available for around $300).
 

·
Premium Member
Joined
·
1,307 Posts
Could you run the fuel line underneath the throttle pedal? When you mash it the whole way down, set it so the pedal pinches off the fuel line, choking supply and limiting it to running on the fuel in the carb only? If you back off in time, it doesn't stall. If you keep it mashed down, you run out of fuel. Just my crazy thought.
 

·
Registered
Joined
·
683 Posts
Could you run the fuel line underneath the throttle pedal? When you mash it the whole way down, set it so the pedal pinches off the fuel line, choking supply and limiting it to running on the fuel in the carb only? If you back off in time, it doesn't stall. If you keep it mashed down, you run out of fuel. Just my crazy thought.
:biglaugh::sidelaugh:ROF:congrats:
best thing i heard all day!!
 

·
CalifornianGravelynator
Joined
·
4,330 Posts
Could you run the fuel line underneath the throttle pedal? When you mash it the whole way down, set it so the pedal pinches off the fuel line, choking supply and limiting it to running on the fuel in the carb only? If you back off in time, it doesn't stall. If you keep it mashed down, you run out of fuel. Just my crazy thought.
no i dont think that would work
 

·
The voice of reason !
Joined
·
2,720 Posts
well yes, but if you have a foot throttle set up like I do, then no. I bypassed mine because the max RPM's the governor allowed weren't quite enough for what I do.
Not enough for what you do ?

Ok I'm curious just what are you doing racing ?
 

·
Moderator
Joined
·
22,781 Posts

·
Registered
Joined
·
210 Posts
Discussion Starter · #12 ·
Not enough for what you do ?

Ok I'm curious just what are you doing racing ?
Anything that involves the phrase "well that was stupid" afterwards. :trink40:

as for the $300 box thing :Stop: bit steep.

as for the governor and throttle stops, That's not as cool as a rev limiter. who want's a boring old governor.

I float the valves just about every time I run my mower. I want to hear the "WHABABABABABABA" that a rev limiter makes, 200-300rpms before my valves float. And I have never seen a rev limiter on a lawnmower, so it's always cool to be the first. :thThumbsU

I've found a couple Tach's with built in rev limiters, but I don't know if they would work for 1-2 cylinder engines.
 

·
Registered
Joined
·
210 Posts
Discussion Starter · #14 ·
I hope the flywheel doesn't come apart on you.
Didn't even think of that...I'll have to build a guard...Thank you for bringing that to my attention. :fing20:
 

·
Moderator
Joined
·
22,781 Posts
as for the governor and throttle stops, That's not as cool as a rev limiter. who want's a boring old governor.
Boring is good. Ask any old pilot. :trink40:

Bob :rauch10:
 

·
Collector of many tractors
Joined
·
15,274 Posts
Run an extra spark plug wire up under the gas pedel...
After it bits you a few time you will keep from pushing the pedel down so far....
 

·
The voice of reason !
Joined
·
2,720 Posts
I like that idea. my main problems right this moment is I'm broke. just figured I would post here and get some gears turnin in peoples heads. Thank you alot.

First I need to find a way to moniter my RPM's. then I guess I can go from there. Any ideas on a *cheap* way to do that?
Hmmmmm ok you're broke but you like to over rev the engine to hear it braapp ?

And who are you trying to impress ?

Because if you keep doing that and blow it up I don't think anyone will be impressed with the 4 foot tall grass because you killed your mower.

I think you should just put it back to stock and use it for what it is a way to mow your lawn.

And if you cant live without that noise get a recording off the internet and use your MP3 player while you mow.

JMHO
 

·
close enuff works for me
Joined
·
3,193 Posts
When the connecting rod comes through the side of the block..:Stop:.It tends to limit the RPM's.....:sidelaugh:sidelaugh
 

·
Registered
Joined
·
537 Posts
I'm trying to think up a way for a Rev Limiter on a lawnmower engine. I know it seems useless for those of you that still have hand controls. but if you have a foot throttle it could be useful for those agrivating times where you get a lead foot and decide to hold the throttle wide open for about 30 seconds... right now my idea is like the throttle control on most push lawnmowers, with the little "flap" inside the shroud that catches the air off the flywheel and regulates the throttle. Well, my idea is to have one of those, and have a little switch wired for a 'secondary' kill wire it pushes when you get to whatever rpm you have it adjusted to 'activate' the switch at. Thoughts? critisism? people telling me to stop bein an idiot and get back to mowing?

:greendr:
That little flap is a govenor, just powered by the air coming off of the flywheel. (try unstreching the tension spring sometime when you have one running, just not for too long) I think you'd get more reliable results using a govenor and tweaking the weights or spring on it. (dunno what style you have on your machine) Whatever you do, keep in mind that most engines were engineered with a certain operating range in mind, and exceeding it can do bad things to the engine.
 
1 - 20 of 27 Posts
Top