A new mower model "Mow All" coming soon...

[JASTN70D]

Re: A new mower model \"Mow All\" coming soon...

Nomad

Maybe spinning is not the way to go at all. I use a finish mower a rotary cutter and a sickle bar mower. The sickle mower can cut much heavier than the rotary cutter and does a fairly nice finish although it is not designed for finish. I think the principle of a sickle could be improved upon to make it a better finish mower. It is harder to manuver though.

 

[fishman]

Re: A new mower model \"Mow All\" coming soon...

Jim,

The Ace Hardware next door has that tool. They sell them in two parts, The eye hoe, and the handle. /forums/images/graemlins/smile.gif

 

[nomad]

Re: A new mower model \"Mow All\" coming soon...

</font><font color="blue" class="small">(
(ratio of inertia forces to gravitational forces)

Are we talking about the same thing?????

Egon
)</font>

Didn't you mention Froude number? So, this ratio gives the Freud number. That is, ratio of inertia forces (ma) to gravitational forces (mg) - If we simplify by taking characteristic length (l), etc., Fr = v^2 / (g l) - Yes, this number can be used in modelling free surface flows (aerofoil, ship, etc), but if the flow around the foil is turbulent, making a model of prototype will be very very difficult (remember simulating turbulent flow is very complex/complicate and it is usually not modelled - only direct numerical solving is efficient today especially if the boundaries are irregular.) Hmmm.. Or, were you talking about Freud number? lol -

</font><font color="blue" class="small">( Nomad

Maybe spinning is not the way to go at all. I use a finish mower a rotary cutter and a sickle bar mower. The sickle mower can cut much heavier than the rotary cutter and does a fairly nice finish although it is not designed for finish. I think the principle of a sickle could be improved upon to make it a better finish mower. It is harder to manuver though.
)</font>

I don't have the sickle pulley sizes at my hand now. With the figures (sizes and rpm) in my mind, I think the linear speed of sickle bar cutter is about 250 ft per minute while it is about 1000-1500 ft per minute at rotary cutter blade if we assume its RPM is about 1000 RPM and blade tip distance to disc center is 1-1.5 ft.- So, assuming the rotary blade mass is more or less equal to sickle bar cutter mass, we can say that rotary cutter blade is applyig a force of 4-5 times more than the sickle bar cutter. So, rotary cutter should be able to cut much heavier tasks than the sickle bar cutter can do. So, why are sickle bar cutter cutting as heavy tasks as, or even heavier tasks than rotary cutter? Simple - sickle bar knives are much sharper than rotary cutter blade, meaning that sickle bar can do the work using much less force due to the sharpness of its blades/knive. Imagine these very sharp sickle bar knives in a rotary cutter rotating around a disk with a 1000-1500 RPM. It will cut even a tree easily. So, yes, I think blades of finish mower and rotary cutters should be made much sharper so that they can do the same work even when they are operated at much lower speeds. Finish mower blade is rotating at about 2500-3000 RPM and this is causing many troubles/problems in finish mowers. If the blades of finish mower were sharper like sickle bar knives, then a low speed like 600-700 RPM would have been sufficient to cut the same grass with same finishing quality. Hey, there are many oppurtunities out there. Who wants me to make him/her such a mower at my home?;-0

 

[Villengineer]

Re: A new mower model \"Mow All\" coming soon...

Nomad, Once again you're living in a theoretical world. I'm not going to attempt to debate you on all your theoretical flow stuff, but you obviously don't understand how these various cutters work or why they are designed different.
First, lets start with the finish mower. Finish mowers are designed to provide a close clean cut with as physically small exhaust clippings as possible on relatively light vegetation. This accomplished in the main design differences from other cutters: deck, blade, and rpm. The deck is designed to create "lift" on the vegetation and to recycle the clippings to have them cut several times thus resulting in the small exhaust particles. The blades are light weight with a relatively sharp edge and some "flap" design to work with the deck to create the air flow to "lift" the vegetation. You see with out this "lift" the finish mower would leave much of the vegetation uncut. The blade must be sharp to cut the grass that is only being held up by air, otherwise it would simply push it out of the way. The high rpm is necessary to create the flow needed. The reason that 99% of finish mowers incorporate belt drive is that it will slip far sooner than a clutch when the light blades contact an object with significant inertia. The cross section of the blade doesn't permit for trying to cut high inertia objects. There is actually very little force applied to a single blade of grass. Think paring knife.
Second, lets look at the rotary or brush cutter. Brush cutters are designed to clear heavy thick vegetation quickly without much regard to how it looks other than it's no longer standing. The deck is designed to let as much in and out as possible. "Lift" is not a concern since it's expected that the vegetation will provide enough resistance to allow the heavy blade to clobber it. The blade edge isn't really all that important either as secondary processing of the exhaust is just icing on the cake if it happens to occur. The high inertia is important to allow to constantly apply this brute force and to reduce stress on the pto and gear box. The heavy cross section blades are necessitated by the high loads applied to them. High loads are regularly applied to single objects. Think claymore.
The last type of cutter we've been discussing are the shear or scissor type cutters. These include reel and sickle bar cutters. These cutters rely on a part or the mower to hold the vegetation and a very sharp knife to cut it off. Speed of the knife has more to do with ability to cover area than the cut itself. The majority of reel mowers only work well with relatively short well groomed grass since they have very tight clearance between the rollers and the reel and simply won't let large objects into the main cutting area. Sickle mowers on the otherhand are capable of cutting larger vegetation based on three main things: Stroke of knife (cutter)/Distance between the teeth (the holding mechanism), the knife itself (rigidity), and available force trasmitted to the blade. Objects which are too large cannot be cut since they can't get between the tooth and the knife. If the object is small enough to enter the cutting area then it will have three basic outcomes: Get cut, break the knife or tooth, or stop the stroke. I've personally seen all three.
The reason the Gravely guys gave you hope is because they are really comparing apple as oranges. I don't remember what their power output was, but I'm guessing that it was less than the tractors we're talking about using a brush cutter. The other big factor is that since they were a walk behind tractor they didn't operate at widths or ground speeds that the equipment you trying to hybrid normally operate at.

Oh, and I can't resist a little dig: If you pull this off I expect your mow-all to be made completely of plastics, composites, high alloy metals, or other "high-tech" materials. It must have an optimized clutch or shear-pin system, cannot cost more than the king kutter brush hog you copied, parts must be available and affordable, and you must make a profit while paying your employees a fair wage. After all this is what you expect from the current equipment manufacturers. I'm not trying to be mean but I hope you understand my point.

 

[Trev]

Re: A new mower model \"Mow All\" coming soon...

Nomad,

I've always had a nagging suspicion that things like rotary mower blades were a bit "low tech." Kind of like windshield wipers, which are basically the same technology the cavemen used to scrape dinosaur droppings off their Nikes. /forums/images/graemlins/smile.gif

How about this.. the PTO drives a generator, which powers a laser. Just move along, and the laser cuts grass, weeds, brush, etc. Never needs sharpening. Maybe laser technology isn't at this point yet.. I don't know.

Bob

 

[jinman]

Re: A new mower model \"Mow All\" coming soon...

</font><font color="blue" class="small">( Maybe laser technology isn't at this point yet.. I don't know.
)</font>
Hey Bob, this laser lawnmower was first posted here on TBN back in the early part of 2001 (when there were less than 50,000 posts). /forums/images/graemlins/smile.gif Hang on to your wallet! /forums/images/graemlins/shocked.gif

 

[nomad]

Re: A new mower model \"Mow All\" coming soon...

</font><font color="blue" class="small">( ... deck, blade, and rpm. The deck is designed to create "lift" on the vegetation and to recycle the clippings to have them cut several times thus resulting in the small exhaust particles. The blades are light weight with a relatively sharp edge and some "flap" design to work with the deck to create the air flow to "lift" the vegetation. You see with out this "lift" the finish mower would leave much of the vegetation uncut. The blade must be sharp to cut the grass that is only being held up by air, otherwise it would simply push it out of the way. The high rpm is necessary to create the flow needed. )</font>

Lets make somethings clear first by asking you a few questions;

1. Does the finish mower FIRST "cut" and THEN "lift" the grass ... OR ... does it FIRST "lift" and THEN make the first "cut"?

2. Is the HIGH RPM of the blade for "lifting" the grass OR is that HIGH RPM was chosen for "cutting" the grass short and easily?

3. Is RECYCLING (cutting the grass again and again) of the grass in the mower deck AIMed in the design (such as to make the clippings in the deck smaller and smaller) ? ... OR ... is it NOT an aim in the design, but only an unavoidable result due to high rpm (because its not so easy to exhaust the clippings without recycling them) ?

4. Do you think, instead of high RPM, a much lower RPM in the finish mower would be enough if much sharper blade (such as sickle knife) were used in the finish mower?

We need to understand why HIGH RPM is used in the mower first, I think.

 

[JASTN70D]

Re: A new mower model \"Mow All\" coming soon...

<font color="blue"> </font>


There is a point about the sharpness of blades that makes a sickle mower cut the heavier stuff but it goes way beyond that . The most major difference is that a sickle mower only deals with the part of the material cut at one point the point of cut is a pinch not a grind effect. Actually the differences are much greater than I could get in to in such a forum. . Maybe you should consider this approach a little more.

 

[Villengineer]

Re: A new mower model \"Mow All\" coming soon...

I don't design mowers, but feel I have a pretty good grasp of how they work. However, I'll try and answer your questions as best I can.
</font><font color="blue" class="small">( 1. Does the finish mower FIRST "cut" and THEN "lift" the grass ... OR ... does it FIRST "lift" and THEN make the first "cut"? )</font> Ok, think of a blade of grass as a beam. This "beam" is cantilevered, has a very small moment of inertia, and, I don't know for sure but I'm guessing, the modulus of elasticity is pretty small, too. You are going to try and apply a force at some point on it's length high enough to cause the beam to fail at this point of force. You should know your beam formulas well enough that the beam would need an additional force to remove the cantilever otherwise it should fail at the ground. Thus the lift must occur at least at the same time.
</font><font color="blue" class="small">( 2. Is the HIGH RPM of the blade for "lifting" the grass OR is that HIGH RPM was chosen for "cutting" the grass short and easily? )</font> Like I stated above I don't design mowers. However, my judgment would be that the answer would be, Yes. I think the high RPM is important for both functions. Since you're a fluids expert you should know that it would be difficult to produce the flow patterns necessary with a simple blade design at low speed. For cutting the blade needs to impart enough force to cut in a very short amount of time or the blades of grass yield and you get an irregular cut.
</font><font color="blue" class="small">( 3. Is RECYCLING (cutting the grass again and again) of the grass in the mower deck AIMed in the design (such as to make the clippings in the deck smaller and smaller) ? ... OR ... is it NOT an aim in the design, but only an unavoidable result due to high rpm (because its not so easy to exhaust the clippings without recycling them) ? )</font> I believe that it is definitely a design goal on finish mowers. Just read the threads on this site pertaining to finish mowers. Nobody wants big heavy piles of clippings lying on their freshly cut grass. The smaller clippings tend to filter down to the ground level, not lay on top. The mulching mower is the extreme of this concept.
</font><font color="blue" class="small">( 4. Do you think, instead of high RPM, a much lower RPM in the finish mower would be enough if much sharper blade (such as sickle knife) were used in the finish mower? )</font> Didn't you read my previous post? The sickle knife operates in an entirely different manner. Besides, you'd lose that very sharp edge rather quickly on a mower blade. I don't want to have to re-sharpen or replace blades all the time. Oh yeah and please don't start talking about special alloys, the blades would cost more than having the 2 seperate implements. Before you ask, back when I was mowing hay with a sickle bar, we would replace or sharpen the knives on a regular basis. Far more often that I want to fool with a mower to use on my lawn. The rpm stuff is discussed above.

As far as trying to market a sickle bar mower as the "mow-all". I wouldn't bother. For the average joe trying to cut grass on his property, they would seem very ackward and quite frankly a little dangerous. But, that's my opinion.

 

[nomad]

Re: A new mower model \"Mow All\" coming soon...

</font><font color="blue" class="small">( ... Thus the lift (and the cut) must occur at least at the same time... )</font>

I quoted only your this sentence first because I feel there is a logic error here.

Both of these actions are being done by the same single object (blade), aren't they? Yes. So, how possible it does two independent actions to another object at the same time? This same time can logically be possible (if possible! - not proved yet) only at the speed of light. SO, in our blades with a speed level of 1/100,000,0... of light speed, there is a time delay/shift between these two actions "lift and cut" - meaning that EITHER the lift is done first OR the cut is done first. I suppose the cut is done first and and then the lift of clippings are lifted to be exhausted out of the deck by the air flow created by the mower blade. I don't think the blade and deck are designed for recycling the clippings (cutting the cliippings over and over in the deck before exhausting them) - they are being recycled because of high rpm values of the blade and because the cavities and small attractor areas (coherent local static flow regions) are occuring in the turbulent flow around the mower blade. To me, this recycle of clippings in the deck actually aren't advantage of a finish mower as you claimed, but it just shows us the blade and deck are NOT functioning properly. In a better designed blade&deck, recycling should disappear.

As for why high RPM in them; I suppose the high RPM mower designers just using high RPM to obtain the sharp cutting by using a blade with thicker cuting edge. This high speed will have an effect on the blade of grass, and we can call this effect "razor blade effect." Later in the history of high RPM mowers, they probably realized that they could use fast air flow created by high rpm blade to exhaust the clippings - but, they had a problem of recycling the clippings because they forgot those cavities/attractors in the turbulent flow field around the blade and probably them these designers are telling everybody that this recycling of clippings is an advantage of finish mowers, which is, in fact, not true, but a problem / design error there.

As for using sickle knive as the finish mower blade; I meant by that if much sharper cutters (around a disc) were used in the finish mowers today, their RPMs would not have to be so high, maybe even 540 RPM would be sufficient. Yes, much sharper cutters will cost more, but don't forget many components of today finish mowers will be cancelled and such a simple finish mower with much sharper cutters with less number of components will cost much less than today's finish mowers which have many components.