Variable power 21'' SP-mower

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Hello,

I just purchased the 21'' self-propelled EGO mower.

While mowing, the motor continuously changes its power.  (I don't mean the self-propelled action, just the power of the blades.)  I am not talking about overheating because it starts to do this even after a couple of seconds of mowing.  Is this normal: does the machine adapts its power to the length of the grass somehow?  Yesterday there was a short time the power was so powerfull I think my neighbours might have been expecting a helicopter landing close-by.  The battery was also empty much quicker than the week before when I mowed for the first time.  At other times, the mower barely makes any noise, making me check whether it was actually cutting or doing nothing at all (it was still cutting, by the way).

As I cannot find anything in the manual or on this forum that indicates the power changes all the time, I post this question.

Another question: the manual says to clean the motor ventilation part.  Where exactly is it located?  I clean the blades and remove the grass on the bottom.

Thanks and best regards,

Pieter
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Pieter Schevenels

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Posted 3 years ago

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lmgagliardi

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I have this exact model and mine does not change RPM at all but reading other blogs on this mower and many people complain about out of control RPM on the 20 inch model.
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David Cline

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There have been a handful of isolated reports of this defect on the 20" mower, but the vast majority are not affected.  The 20" mower is a constant 600 watt power, and if you hit a dense spot of grass the blade will bog down since power doesn't increase to compensate like it does on the 21".
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Wrog

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Mine adjusts power output when it hits a patch that's thicker and harder to cut but I wouldn't say it's constantly changing.
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Exrace

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This is normal and how the mower conserves battery power for longer run times. With current blade on the 21 the achieve longer runtimes at the expense of lifting power. If and when the higher lift blade is available in the states you will probably notice this less with that blade installed as that blade  takes more energy to keep the blade at ~2800 rpm's
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David Cline

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The high lift blade will slightly increase the resistance on the blade, and thus increase the power drawn by the motor.  Ego has said to expect a 10-15% increase in power consumption (and thus an equivalent decrease in run time).
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David Cline

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Yes, the power changes on both 21" models, but it goes much higher on the 1,000 watt self propelled version than the 700 watt push version.  If you are cutting dry grass and aren't taking much of the blade off then it is actually slower and quieter than the 20" model.  If you are cutting very thick grass, taking more than 1/3 of the blade off, or the grass is wet then the motor will sense the resistance start to slow the blade down and increase the power.  Once the resistance has decreased, the power will drop back down.

Yes, this makes the battery's run time on a single charge shorter, and if it stays at an elevated power level for most of your mowing then you will notice a significant difference in run time.  The manual may not explicitly explain the variable power feature, but it does explain the expected run time for different types of mowing.
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David HD, Champion

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Official Response
Pieter, if you have nothing "interesting" to read this weekend, then spend your time reading this great article on "What is a Brushless Motor and How Does it Work?" by Chainsaw Journal.  This article breaks down the "how" and the "advantages" of a brushless motor.  This article was written about the EGO 56V Chainsaw, even though I don't own or need a chainsaw, but it was very informative with great exploded views of a "brushless motor."  I am a visual person and this article was perfect for my taste, hope you will enjoy it!

Advantages of the brushless motor:
  • The lack of brushes ensures that there is low friction during the operation of the motor and reduced production of heat, therefore, increasing the durability of the motor.
  • The minimal heat and motor wear due to lack of mechanical contact on the motor vastly improve power transfer and electrical efficiency that leads to increased performance and power.
  • The increased efficiency of the brushless motor helps to prolong battery life up to 50% or more.
  • There is no sparking and the motor produces less electrical noise.
  • Heat dissipation is better since the stator where the windings are located are connected to the case.
Disadvantages of the brushless motor:

The initial cost of the motor is high due to the need for commutating devices such as the encoder and a controller or drive.

https://www.chainsawjournal.com/what-is-a-brushless-motor-and-how-does-it-work/

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David Cline

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None of the current Ego mowers have a brushless motor.  Ego has said that their engineers determined for this application a brushless design was not as effective.
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David HD, Champion

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Interesting!  Kobalt 80V, Ryobi 40V and Echo 58V all use "brushless motor" with their lawn mowers.  I wonder if they will follow EGO or stay the course?
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Blue Angel, Champion

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I've seen several instances where a new brushless tool was outperformed by a brushed model. It would seem that simply using a brushless motor as an advertising gimmick is all the rage as people assume they're better.

A good brushless motor WILL outperform a good brushed motor, the results have been well documented. However, it seems a good brushed motor will still outperform a poorly designed brushless motor.
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TheAtomTwister

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I think that it depends on the application, but I'll look into it further. Also, with brushless motors, the controller matters, how it is wired and how it is programmed if programming is involved. 

Personally, I'd rather the RPM be controlled by a variable-speed lever, and same with the speed the mower moves forward at.  The mowers that automatically change the speed at which their blades spin that I have encountered are too unreliable for me, plus, I will ramp up the blade speed before hitting tall grass so the blade's rotational momentum will cut the grass.
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David HD, Champion

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I agree with you.  That said; I found this article on "brushless" vs. "brushed" motor by SL Montevideo Technology Inc.  For a "brushless" motor, one of the CONS is higher cost of construction vs. a "brushed" motor.  Whereas the PROS for a "brushless" motor is high efficiency vs. poor heat dissipation of a "brushed" motor.  So based on this article, it appears that a "brushless" motor cost more to make - but yield higher efficiency and speed range.  So the question remains, why wouldn't more cordless power tools be made with "brushless" motor instead?

http://www.dynetic.com/brushless%20vs%20brushed.htm

Brushless Motor

Pros
  • Electronic commutation based on Hall position sensors
  • Less required maintenance due to absence of brushes
  • Speed/Torque- flat, enables operation at all speeds with rated load
  • High efficiency, no voltage drop across brushes
  • High output power/frame size.
    Reduced size due to superior thermal characteristics. Because BLDC has the windings on the stator, which is connected to the case, the heat disipation is better
  • Higher speed range - no mechanical limitation imposed by brushes/commutator
  • Low electric noise generation
Cons
  • Higher cost of construction
  • Control is complex and expensive
  • Electric Controller is required to keep the motor running. It offers double the price of the motor.

Brushed Motor

Pros
  • Two wire control
  • Replaceable brushes for extended life
  • Low cost of construction
  • Simple and inexpensive control
  • No controller is required for fixed speeds
  • Operates in extreme environments due to lack of electronics
Cons
  • Periodic maintenance is required
  • Speed/torque is moderately flat. At higher speeds, brush friction increases, thus reducing useful torque
  • Poor heat dissipation due to internal rotor contsruction
  • Higher rotor inertia which limits the dynamic characteristics
  • Lower speed range due to mechanical limitations on the brushes
  • Brush Arcing will generate noise causing EMI
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TheAtomTwister

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Electronics can be sealed in a heatsinking compartment that waterproofs and keeps cool the electronics.  Personally, I'm sticking with brushless just because I know how to use brushless motors and I have more control over what they do than I do over what brushed motors do.  If I can get the damn thing out of the 530CFM EGO blower, I'm gonna put a scorpion HK-3226-1400KV motor in it if it fits. It'll fit my 80V blowers, I sure hope it fits the EGO.  The link to that motor is here: http://www.scorpionsystem.com/catalog/helicopter/motors_4/hk-32/HK_3226_1400/ for those that are curious.  I will have to make a controller for it as well. I do not know how much air that will make the blower move, but I know that it will be quite a lot. There will be a turbo switch and an overclock switch. Currently on turbo, the 530CFM blower draws about 750W, and when the modifications are complete, high will draw around 1250W, the turbo, which can be used continuously, will draw 1770W, and the overdrive will give a 2 second burst of 2330W and have a cooldown that will depend on the temperature of certain parts of the motor. When the motor is cool enough, the overdrive switch will be unlit. When it is active, it will light up green, and when the motor is too hot for overdrive, it will be lit red.  I will probably put a shoulder stock on the back of it to make it more ergonomic when it is putting out so much thrust.  Anyway, that's enough blower talk, this is supposed to be about the mower.  I do think that I might be able to find a way to make a brushless motor work better in the mower than a brushed one does, but it depends on the brushless motor's configuration. A lower number of stator arms might be desirable, I'll just have to try different motors.
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Blue Angel, Champion

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TAT, what's the RPM range on that motor? The web page doesn't provide it.
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Blue Angel, Champion

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DHD, all good info.

Looking at a cordless drill as an example, if a brushed motor costs the company $5 to make and a brushless motor costs them $10 (twice as much), but they can sell the drill for $30 more with the brushless motor, that makes good business sense. The performance might be the same or even worse with the brushless motor, especially if they cheap out on the control electronics.

I watched a video testing cordless planers, which are relatively simple devices and were being tested on the same material. An older brushed Makita model had both more power and more run time than a newer brushless model, I think it was a DeWalt. Yes, one can argue that the tool is a system and there are other variables than just the motor, but the difference was quite large in both power and run time, a result that was rather surprising. It opened my eyes.

Then we see the brushed Ego mowers competing with brushless models from other companies and being rated top of their class. Once again, lots of variables but it's still a data point.

I love the idea of a good brushless motor, and some of the tools that use them are absolutely incredible. Ego's blowers and my Makita drill come to mind, both of which offer power that defies the look of the tool.
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David Cline

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That's the important thing to remember—the competition may use brushless motors, but objectively the Ego performs better.
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TheAtomTwister

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I don't know what the RPM range on the Scorpion is, but what I'm going to do to find out is increase the RPM until it rips itself apart.  I do not think I'll need it to exceed 50,000 RPM. I do not think it will be able to exceed or even make it close to that speed with the EGO fan when using 2330W of power, for the kinetic energy of the air octuples when you double the volume and the speed, and more than 46000RPM will be needed for that, but there really is only one way to find out. I'm willing to bet that it can handle up to 80,000 RPM.
(Edited)
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TheAtomTwister

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Dude, holy crap, look at this motor, it can handle up to 13,000W. God, if you put that in the backpack blower, it would be able to put out as much force as the Billy Goat Force 18 for just under two minutes on the 7.5Ah.

Here's the motor: https://www.amainhobbies.com/xnova-xts-4535520kv-44yy-brushless-motor-shaft-a-xnmts4535520-a/p508052 

Here's the Billy Goat: http://www.leafblowersdirect.com/Billy-Goat-F1802SPV-Leaf-Blower/p7541.html
(Edited)
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David HD, Champion

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TAT, at $490 for just the motor, the backpack leaf blower would probably retail for $900 or higher - that would be "one heck" of a blower!!!!!  Plus, you would need (2) 7.5 Ah batteries to keep up with the demand - but would be nice to try it if they can build it.
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Blue Angel, Champion

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Pretty crazy motors!
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TheAtomTwister

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Actually, you would need 5 7.5Ah batteries to stand the 255 amp current draw. Also, I believe that such a draw would only work in bursts without overheating the motor. It is probably best to run it at 6.5kW, which is still well over the 3.3kW of the Husqvarna 580BTS.  It is also probably better not as a backpack but as a walk-behind blower.
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David Cline

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I have one of those... a gas-powered walk behind. It seemed like a great idea when I got it, but it's actually quite a pain to maneuver if you miss anything in a single pass. Probably would be best in combination with a backpack blower.
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David HD, Champion

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The last time I saw one of those "walk-behind" blowers was when I was in elementary school.  They are powerful but bulky (to David's point) so I don't imagine "residential" use is high vs. commercial.
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bloomz

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Mine rarely changes speed, if it was constantly I'd be calling support.
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David Cline

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How dense is your grass?

Mine drops back down to low power at the end of every pass, whenever I lift the mower to turn, or if I slow down or stop for a moment. The slowdown is pretty quick, but the ramp up is more gradual, so it does seem to constantly be changing—unless I have enough grass buildup under the deck that it doesn't drop back down and just stays high.

You can always call support if you are concerned, but hearing the power modulate up and down on a 21" mower while mowing certainly isn't anything unusual that you should be worried about,
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Pieter Schevenels

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Thank you all for the (quick) comments.  I guess most of them are reassuring.

It is all new grass since July.  The shadow zones have quite high and thick grass and the zones in the sun are easier for the mower as the grass still has to grow dense there.  I guess that explains the change about every minute.  So I guess the noise is decreasing when thicker/higher grass is being mowed as the rpm is lower (but the power higher), as I understood from one of the replies.  While mowing, this didn't seem logically but now it does.

And indeed the first time I mowed at height nr. 5 and yesterday at height nr. 4 which probably explains why the battery was empty faster.

At last, indeed the slow down is quick and the ramp up is more gradual.