Titanium blade

[prb238]

I was discussing the height modification with another Lawnbott owner and the discussion went to the idea of a titanium blade and if it would hold up better when hitting an object in the lawn and also stay sharp for an extended period of time. I am going to produce a titanium blade and see what happens.

The stock blade for the 32xx series is 12" in diameter and is .0300" thick.

I am going to try .0200" and .0170" thick titanium plate and see how they hold up.

I've got a metal cutting bandsaw that I'll use to cut the sheet - hopefully it won't work harden too much and I can get through the material with it being pretty thin.

I'll report back and let you know how it goes.

Paul

[AGR]

Make sure if there is extra weight that it wont hurt the motor, which is already prone to an early death. But, if it is not too expensive sign me up. I have a pile of 5 or 6 that I constantly hammer flat and sharpen.

[prb238]

Yeah - good point on being careful with the blade motor. Remember that titanium is lighter than steel and stronger.  My first thought was to shape the titanium into the exact same blade configuration/shape but since the titanium is stronger I am thinking about making the blade protrusions thinner, heck, I may even make an 8 cutter blade and see how that works.

With the height mod I notice the grass doesn't get a clean cut with 1 pass ( taller grass tougher to cut maybe?). Or it could be that my blade is not sharp enough. Seems like I have to sharpen it very frequently. Again, another plus with the titanium approach - it may be tougher to machine the cutting edge but once it is there I bet it stays sharp much longer.

I have slightly thinner titanium sheets than the stock steel blade so I'll have to see how flexible it is when I get it. The titanium should come in early next week.

[prb238]

So I finally got around to creating a titanium blade although I have not tested it yet. I made the blade sections a little less wide than the stock blade. The new blade is very light!!  I am working on sharpening it. As soon as I am done I'll post a picture. I used a sheet that is thinner (.020") than the stock blade - I may get another sheet of titanium the same thickness as the regular blade and try that as well.

Like I said below I may also try more blades as well since the titanium is lighter.

[toolbelt]

I also noticed that when the grass was high it took a second pass to give it a clean looking cut.  Maybe the grass is bending over such that the blade is sliding on top of the grass instead of cutting.  The gas powered lawn mower blades are built such that they create a suction to pull the grass up.  When you make your new blades maybe you want to add a pitch to the blade.

[Botman]

Any concerns that the lighter blade could cause higher RPM's because it's lighter?  Not sure if the motors are regulated to RPM's.

[moselco]

Hi, there is a sensor on the blade motor that measures resistance on the blade.  I am not sure what will happen with the lighter blade.  Just a guess, it will probably be fine.  There is a smaller blade that is sold to customers having very thick grass.  There is less resistance on the blade so the robot can get through the thickest parts without getting bogged down.  This smaller blade would be lighter, so my guess is the weight won't cause a problem.  The RPMs may be different but I doubt you could detect it.

Cheers,

Robotlady

[prb238]

@Toolbelt - great idea on the pitch of the blade.  I looked up high lift mower blades and there are some key features that they all seem to have these days.  It appears that the upward curvature behind the cutting edge of some of them has to do with ushering the blades of grass into the chute for bagging or if you mulch, it throws the grass clippings up against the deck so they fall down and get cut again into smaller pieces.  Using the Bernoulli effect, it would make sense that if the air is moving slower on top of the blade as compared to underneath, it will create a suction upwards - just like what lifts a plane off the ground.  So, some type of curvature on the blade makes sense to try.  I will experiment with this and use some regular mower blades as a model and see what happens.

With my grass getting cut taller (currently have it set to almost 4"), having the grass pulled up to get cut would definitely make a cleaner look and maybe cut all the grass in one pass.

@Botman and moselco - good questions and thoughts on the RPM's.  I am thinking that with a curved blade, the resistance on the blade as it spins will be greater.  I noticed that some of the high lift mower blades on the market today actually have sections cut out of the upward curved section behind the cutting edge - I bet that this is designed to reduce drag but still provide the upward air motion.  With the titanium being lighter and with a cut out design, and in addition to knowing now that the manufacturer offers a smaller blade, I am less concerned now about the effect on the blade motor  .

Keep in mind that a curvature on the blade will mean lowering the blade a bit to allow room for the curvature so it doesn't hit the underside of the mower deck.  I'll have to play around with how much curvature is necessary and how tall the upward curving section needs to be.  I noticed that there is some variation out there with existing high lift mower blades with these two parameters.

Thanks for the feedback everyone!

Paul

[RobotLady]

A customer recently pointed out that the blade is mounted at a slight angle.  I wonder if a small amount of upward suction is already present.  It can't be a lot, though, because I've noticed the Lawnbott does not disturb mulch as it passes over it with the blade running. 

Robotlady

[shep874]

While you are tinkering with the blades.  let me suggest making a holder for box cutter blades...  I saw this on a home made robotic mower somewhere but cant find it now... sure would be more economical.   

[prb238]

I've seen that before too Mel, maybe a YouTube video if I remember correctly.  Good idea - would be nice to have that option as well.  I'll add that to the list of tinkering ideas .

[JeffinNJ]

Hi Paul! Any news on the Ti blade? I hadn't thought of going thinner. When I raise my blade as high as possible, any blade flex leads to housing collision.  My initial reason for suggesting Ti was to increase thickness and rigidity to reduce flexing and hopefully, increase blade life at higher cut heights.