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grass cutting robot
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Please be positive and constructive with your questions and comments.

grass cutting robot

by roby on Sat Feb 06, 2010 7:15 am

I recently found an interesting article on a home made grass cutter robot. The author suggests using a 12V battery pack and a solar panel to keep it going. The motors are therefore all 12V. He uses a PIC.
Due to very limited knowledge (I have just finished the experimenters kit), could someone please confirm that the Arduino ATMEGA328 is capable of doing the job?
I believe the 3 motors (2 for movement and one for the blade) can be controlled by the Arduino with 1 transistor and one resistor per motor, or do you believe it's necessary to purchase specific drivers?

Thank you.

roby
 
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Re: grass cutting robot

by uhe on Sat Feb 06, 2010 6:48 pm

I'd say the arduino is powerful enough to control such a robot. For the motor(s) you should use a dedicated driver. Maybe a L293D or a L298 but i don't know if one of theese can handle the load. The L293D is used in the Adafruit Motor Shield.
IHMO it'll be easier to modify an existing cutter insteed of building one yourself from the ground up ... the blade ... safety stuff... hmmm
Just add 2 motors for movement and a relay to switch the blademotor on/off.
"I have not failed. I've just found 10,000 ways that won't work." - Thomas Edison
uhe
 
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Re: grass cutting robot

by adafruit_support_bill on Sun Feb 07, 2010 8:54 am

No need for a full H-bridge driver if you don't need to reverse the motors.

You can do it with just a transister and resister per motor, but it is better to add a snubber diode to protect against reverse voltage generated by the motor when starting and stopping.

Here's a good tutorial:http://itp.nyu.edu/physcomp/Tutorials/HighCurrentLoads

adafruit_support_bill
 
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Re: grass cutting robot

by aburton on Sun Feb 07, 2010 3:20 pm

arduwino wrote:No need for a full H-bridge driver if you don't need to reverse the motors.

You can do it with just a transistor and resistor per motor, but it is better to add a snubber diode to protect against reverse voltage generated by the motor when starting and stopping.

Here's a good tutorial:http://itp.nyu.edu/physcomp/Tutorials/HighCurrentLoads




I'm currently using this tutorial to drive a 12v, 12A motor using an IRF540 to drive the motor, and a RURP3020 snubber diode.

I've been told that looking at the datasheet, I need to use an NPN transistor to bump up the voltage to the IRF540 to around 7v to keep the IRF540 more efficient. Do you understand the reasoning behind this? Do you know how one would go about doing this?
aburton
 
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Re: grass cutting robot

by zener on Sun Feb 07, 2010 6:50 pm

Mosfets need a certain gate voltage to operate well. Some need 10V and some need 5V. Some only need 3V or less. Gues where this mysterious information resides????? On the data sheet! I believe the IRF540 likes 10V and I am guessing you are giving it only 5V. But my crystal ball is going cloudy... Another solution is just use a fet designed to operate at the gate voltage you have. Something like IRLZ44 etc. However, if your 540 isn't getting hot then it is probably OK.

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Re: grass cutting robot

by roby on Mon Feb 08, 2010 1:26 pm

The body of the grass cutter is made to cover the blade and to make it safer I also intend to add a "tilt" sensor that cuts off the power should the robot be tilted or turned.
For the blade I am looking for a high efficient brushless 12V motor that is normally sold for model airplanes: they are light weight and quite reliable. They also have only 3 wires that need to be connected to a driver (which is a plus for a newbie like myself). I hope someone at MOOG will tell me where/how to connect the other 4 wires that go from the driver to the Arduino (unless someone has any suggestions... :wink: ).
For the 2 wheels, since these need to go back and forth, I presume the 2 motors will need a different type of driver.
For what regards the terms used in your replies, I understand the concept of voltage increase created by a Mosfet or a transistor (even if I do not yet know how to calculate them and the circuit needed). I am not familiar with IRF540, L293D, H bridges or snubber diodes.
Let me study the tutorial indicated and hopefully I will have more technical questions that you can kindly answer.

Roby

PS. If there are any other tutorials that might help, please let me know. Thank you.

roby
 
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Re: grass cutting robot

by roby on Sat Feb 27, 2010 2:19 pm

I have identified the 2 gear motors needed to get the grass cutter moving.
Technical info:
- 12 Volts
- no load current: 140mA
- current at max. torque: 580mA

I've read some tutorials, but I'm not sure I could get away with making an H bridge so I believe it best to go with a driver.

I read on the Arduino motor shield specs that it is made to provide up to 600mA per motor. Before I order one could someone kindly confirm that the motor shield will work continueously with this amount of current? Theoretically it should run all day.

Has anybody purchased the book "Make: Electronics" by C Platt?
Thank you.

roby
 
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Re: grass cutting robot

by roby on Wed Mar 03, 2010 1:17 pm

Well, no news is good news: if adafruit didn't answer, I guess the request for info on the motor shield was probably a dumb question.
So I might wait on the book, but I will purchase the Arduino motor shield.

NEXT QUEST: sensors.

I narrowed the research to 2: Maxbotix and SRF010.
I am pointing at SRF since I have found more info and tutorials to help a newbie like myself.

If anyone thinks the Maxbotix is better and knows where to find basic info and/or a tutorial, please :D let me know.
Thank you.

roby
 
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Re: grass cutting robot

by Bob Gross on Thu Mar 04, 2010 11:19 am

MaxBotix Inc., will offer email support while you do the project.

Also, our XL line of sensors have very good noise immunity and will likely work with more background noise than other sensors might tolerate. Depending on the sensitivity needed I would recommend our XL-MaxSonar-EZ2 sensor (or the XL-MaxSonar-EZ3 or the XL-MaxSonar-EZ4). Just look at the data sheets for detection zones to objects and choose the sensor that matches your application. Also, even our LV line of sensors will tolerate background noise, provided the noise was present during the first reading taken by the sensor (generally power up for most users).

Bob Gross
CEO MaxBotix Inc.
http://www.maxbotix.com
(I noticed your post during a web sweep. Not always here so for support, you can email us).
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Re: grass cutting robot

by roby on Sat Mar 20, 2010 3:12 am

I have checked the Adafruit and MaxBotix sites and there are some interesting sensors, there is one specifically for out door use which should be very useful with a grass cutting robot. However on the SRF there is a lot more information in relation to the Arduino (ex. a tutorial on how to asign an address and also a specific library), so as a first project I feel more confortable with the SRF.
Waiting on the shield, sensors and motors to be delivered in order to start the hardware assembly. Then it will be time to start working on the software...

roby
 
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Please be positive and constructive with your questions and comments.