Let's Make Robots!

M.T.M.P. + Grass trimmer

Well... bad choice of the motor I guess. I use 2 brushless motors from a quadroter.

The motor is getting slow after cutting grass for seconds. If I have it spin freely it runs OK as long as it should. Any ideas??

(I use 30C 3S lipo 5AH, shouldn't be power problem. )

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Good job. your cutting wire system looks powerful and light.Have you some else photos of your job?

That looks like a really fun way to mow your lawn. Awesome project!

I am wondering at the long pauses in between movement phases.  Is it calculating something, or perhaps taking readings?  It really looks like when it moves, it still has plenty of power.

I don't know how much current that battery will supply in a surge, but a problem I ran into on my present project was that, while my battery has enough stored charge (2.5 AH) overall, the instantaneous or surge current available from the battery is not high enough. What happens is that my terminal voltage drops from 5 volts down to about 2 volts fairly quickly, but after switching off just a few seconds, the battery voltage comes back up to 5 volts again. If I only run the microprocessor and such, the voltage stays up, but when I run the motors, it has that annoying voltage drop..

Since the voltage will not come back up like that if the battery is truly discharged, it means the current near the terminals is drained off, and has to be recharged by charge migrating from within the battery to the terminal area.  The rate the charge can move or migrate within the battery is too low. Solution: I either need to add another battery pack in paralell, so each only supplies half the surge current needed by the motors, or buy a different battery like an SLA* type, that will allow a higher current draw.

I don't know if that applies in your case, but it is something you can check.



Possible like what you said. These brushless motors are just not suitable for this job. Thanks for input.

I was thinking even this


beside, it looks more "KILLER". Ha~

Thanks for you guys advices. Yep, that motor just not right to do such job. Gotta find some used trimmer from local or craiglist. Ebay doesn't have much choices. Thanks again!

Look for a used cordless weed-whip on craigslist/ebay/local and just hack it up as an attachment/accessory...

BTW - very nice platform hardmouse

You need stronger motors. Since the grass is giving them a quite strong resistance (dunno how else to say) they draw a lot of current. Maybe your battery can't deliver that much. In order to run smoothly the motor have to be strong and the battery have to deliver enough jusice to keep them spinning with high velocity.

But as your battery is already big maybe your wires to the motors are to thin? Also the motors for quadcopter might not have enough power since they just have to "cut" air. Just my 2 cent but hope it will help debugging ;-)

BTW, interesting construction with the cutting wire.

EDIT: Saw the video now and think that you need more torque. The motors are really just made for the copter and not for high torque usage. And try to slow down your bot to get a stable speed all the tme it's cutting the grass.