Possible lanwmover motor ?

[speedy]

Hi !

do you guy's think this motor would be enough to power the 33inch rotor on a lawnmover in direktdrive config or possybly geared on 12s lipo ?

[DrKnow65]

Is there a link in there somewhere?

[speedy]

ops ! sorry !



http://www.hobbyking.com/hobbyking/s...dProduct=14427

[What's_nitro?]

12s @ 150KV is 6750rpm. You would need to gear it somehow. A 2:1 ratio should be OK since most mowers run in the 3000rpm range. I'd recommend a V-belt drive just in case you hit something harder than grass....

[What's_nitro?]

...and you will need VERY GOOD batteries to power that beast. Figure for a 200A constant draw, 300A spike. The load of swinging a heavy metal blade through grass must be >/= a large prop.

[speedy]

But the stock ice engine only produces 3,5hp ? So this outrunner chouldn't need to work hard at all?

[What's_nitro?]

The stock engine bogs down when it hits a load. An electric motor will just draw more power and not bog down (assuming the other components can handle it). I'd expect it to want ~5-7HP in a 21" mower. So unless your grass doesn't grow very well it's going to be more powerful.

[BrianG]

That motor is not a good choice IMO. 11A no load current @ 20v is rather high, which means 220w of power loss due to inefficiencies.

As said, you will need one heck of a good power source to spin 33" of blade to cut grass. Even your 3.5HP is 2600w, which is probably a lightly loaded constant figure. I too think ~7HP is more reasonable value for such a large blade. To keep current draw down as low as possible, you'd have to use the full 70v on that linked motor, gear it down, and even then you it's gonna draw 75A constantly (for 7HP). I don't know the size of the area to mow, but that current will require over 1250mAh per minute of battery capacity, and that's not counting efficiency losses. So, to mow a lawn that takes 20 minutes, you'll need a 70v (19s) 25Ah battery.

[What's_nitro?]

Wow! I completely missed where it says 33" cut.

Is there one blade, or two? I guess you could spin the blade slower (2500rpm?) and use less power, but it'll still be a lot more than 3.5HP.

[speedy]

The lade is 33inches in diameter

[killajb]

I think the idea is neat, perhaps a different approach..

With the motor referenced, one would surely need quite a few batteries to keep things happy. Assuming you were going to go ahead with that, I'd ditch the blade for a string set-up (think weed eater). Something that swivels under low rpm, yet is thrown outward under the centrifugal force of 6000 or so rpm to cut grass.


Or.. if you wanted to pick another motor, a permanent magnet DC motor perhaps.. the desired rpm range can be met easier. Here's a good example: http://www.robotmarketplace.com/prod...MC-ME0909.html

[BrianG]

I was contemplating a lawnmower project a while back and discarded it once I started figuring the power requirements involved. Like you, I thought about a string "blade", but decided it was more work than it was worth.