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Thread: motor/gearbox for heavy lawnmower-rover?

  1. #1
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    Question motor/gearbox for heavy lawnmower-rover?

    Hey, first post here on these forums.

    I recently started a Lawnmower/fertilizer-rover project but ran into an issue finding a motor/gearbox combo that will work with my setup.

    I seem to like phidgets because it removes the electrical engineering component and allows us software engineers to just dig in , in practically whatever language we want. it's also very easy to integrate into commercial app!

    For previous (smaller) projects, I have been using the phidgets 8/8/8, servo-controller and high-current motor controller. If possible, I would like to use the same motor controller for this project. I have just been having trouble finding a motor/gearbox combo that would be suitable. I am also interested in using the phidgets high-speed-encoder to keep track of wheel position + speed.

    I thought I found the solution with the parallax MotorMount and Wheel Kit with Position (http://www.parallax.com/Portals/0/Do...Mount-v1.0.pdf)

    but after speaking with Alex @ Trossen for a while, he said I would not be able to use that kit w/ phidgets (the encoder signals are not compatible). He also said he did not think it would be able to push this heavy rover (max 100lbs with batteries and fertilizer-spreader and all the other goodies).

    Edit: I have seen this project done a few times times with wheelchair/powerchair motors, but since I'm lacking the electrical understanding, I am not sure if those motors will work with the phidgets components.

    Anyone have any suggestions?

    Thanks in advance!

    -Carmine
    Last edited by wrongprotocol; 04-29-2009 at 08:08 AM.

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    Re: motor/gearbox for heavy lawnmower-rover?

    You mention 100lb weight for the robot -- thats really big.... add a cutting deck and that's really dangerous.. anyways - what kind of yard do you intend to mow? The motors required for a completely flat area will be significantly lighter duty than those required to scale a 35 degree incline.

    How do you plan to navigate? Are encoders really necessary?

    I think you will likely end up wanting something in the ballpark of wheel chair motors, current anywhere from 15-75A at stall... WAY more than the phidgets will handle.

    -Fergs

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    Re: motor/gearbox for heavy lawnmower-rover?

    Hey Fergs,

    Thanks for the reply,
    the 100lb weight is a predicted max weight - the deck is built ontop of the lawnmower. I removed the wheels from the mower, build an angle-iron frame around it and [this part isn't done yet]plan to attach my own set of wheels to the angle-iron frame. Currently planning for swivel wheels in the front and fixed powered wheels in the back. This will not have to handle anything beyond a slight grade, no big inclines. Just a large area of flat land.

    I will hold off on autonomous until everything works fine with R/C. Over the weekend i wrote some code to control a minibot along with a pan/tilt webcam with a logitech joypad over wifi. I also put in some sonar + IR rangefinding but I wont be using that until autonomous.

    I went wifi because it's what I already have. the bot (as of right now is not a lawnmower, but just a rover) has a laptop on top with the phidgets stuff and webcam connected. I run the phidgets web interface on the laptop, and I encode and stream the video.

    The rest of the processing is done on the computer in my house. I chose java as my language because I can prototype very fast in it. I can currently drive the small test-bot via my gamepad, see the sensor readings, and view streaming encoded video (with a .1 sec delay but that's good enough for a lawnbot).

    If all goes well, I will add some simple autonomous logic. There isn't much to hit in this yard, it would just be important to cover all of the ground area.
    Last edited by wrongprotocol; 04-29-2009 at 08:25 AM.

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    Re: motor/gearbox for heavy lawnmower-rover?

    I think you will likely end up wanting something in the ballpark of wheel chair motors, current anywhere from 15-75A at stall... WAY more than the phidgets will handle.
    It really depends though Fergs. If there is a PWM driven motor controller that can handle higher Amperage (ie. BaneBots has a 45A peak, but it's only 12A continuous), then you can easily hook it up to a Phidget Servo Controller. I'm saying "if" because I have no clue if there is one or not. I'm a little out of my element with this one, but I still wanted to throw the concept out there

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

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    Re: motor/gearbox for heavy lawnmower-rover?

    side question: 7 years ago, junior yr in highschool, we had a FIRST robotics team. Our bot was heavy, and we had used the powerwheels motor/gearbox. it didn't have to tread through grass but it had No problem moving that bot. I havn't done any with FIRST since then, so im not sure if they are using the same motor/gearbox kit. Anyone know about that? Would that be compatible with phidgets motor controller?

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    Re: motor/gearbox for heavy lawnmower-rover?

    Quote Originally Posted by Alex View Post
    It really depends though Fergs. If there is a PWM driven motor controller that can handle higher Amperage (ie. BaneBots has a 45A peak, but it's only 12A continuous), then you can easily hook it up to a Phidget Servo Controller. I'm saying "if" because I have no clue if there is one or not. I'm a little out of my element with this one, but I still wanted to throw the concept out there
    Sorry, I meant to say "phidgets motor controller" not phidgets in general. I'm sure there are servo-signal driven motor controllers that can source 20-30A continuous and 75A stall... look towards battlebot stuff.

    -Fergs

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    Re: motor/gearbox for heavy lawnmower-rover?

    Quote Originally Posted by wrongprotocol View Post
    side question: 7 years ago, junior yr in highschool, we had a FIRST robotics team. Our bot was heavy, and we had used the powerwheels motor/gearbox. it didn't have to tread through grass but it had No problem moving that bot. I havn't done any with FIRST since then, so im not sure if they are using the same motor/gearbox kit. Anyone know about that? Would that be compatible with phidgets motor controller?
    The bigger powerwheels *might* be able to carry 100lbs for an extended time... but with a shortened life (especially when you add treaded wheels). That said, those motors are really cheap and thus inefficient... so shorter runtimes + higher current (still higher than the phidgets motor controller can handle most likely).

    Alex had a good call on phidgets servo + servo-pulse motor controller...

    -Fergs

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    Re: motor/gearbox for heavy lawnmower-rover?

    Quote Originally Posted by Alex View Post
    If there is a PWM driven motor controller that can handle higher Amperage (ie. BaneBots has a 45A peak, but it's only 12A continuous), then you can easily hook it up to a Phidget Servo Controller.
    I'm a bit confused - why a servo controller instead of the motor controller? can it handle higher current than the 'high-current motor controller' ? or is it because it can send data?

    I have been calling around asking about the wheelchair motors to get an idea of price and if they are even available. But I still face the problem of figuring out how to use it with the phidgets. I dont know enough to integrate the banebots speed controller with one of the the phidgets devices.
    Last edited by wrongprotocol; 04-29-2009 at 09:08 AM.

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    Re: motor/gearbox for heavy lawnmower-rover?

    I'm a bit confused - why a servo controller instead of the motor controller? can it handle higher current than the 'high-current motor controller' ? or is it because it can send data?

    I have been calling around asking about the wheelchair motors to get an idea of price and if they are even available. But I still face the problem of figuring out how to use it with the phidgets. I dont know enough to integrate the banebots speed controller with one of the the phidgets devices.

    There are several ways of controlling a DC motor. One way is like this:




    This setup uses two controller boards. You have a servo controller and a DC motor controller. The DC motor controller needs signals from the servo controller (PWM or pulse width modulation) to control the speed and direction of the servo.


    From the Motor and Servo Controllers page:

    Controlling a DC motor from a computer is best done as a two stage process. Servo controllers output a PWM signal which the DC motor controller accepts. This allows a developer to custom build a solution for their needs much easier than trying to hunt for the perfect integrated solution. A servo controller can be chosen that has the type of connection and API needed while a DC motor controller can be selected separately to match the motors being driven.

    �In the long history of humankind (and animal kind, too) those who learned to collaborate and improvise most effectively have prevailed�
    - Charles Darwin

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    Re: motor/gearbox for heavy lawnmower-rover?

    Quote Originally Posted by wrongprotocol View Post
    I'm a bit confused - why a servo controller instead of the motor controller? can it handle higher current than the 'high-current motor controller' ? or is it because it can send data?

    I have been calling around asking about the wheelchair motors to get an idea of price and if they are even available. But I still face the problem of figuring out how to use it with the phidgets. I dont know enough to integrate the banebots speed controller with one of the the phidgets devices.
    The idea is this: the servo controller takes input from your computer and outputs a signal (low current, low voltage), that then is input into a motor controller. Where a hobby servo would normally turn this signal into a position output, the motor controller takes this signal and instead turns it into a motor speed. The servo controller doesn't even touch the motor, just sends a signal to the motor controller (since the motor controller lacks the easy-to-use USB interface you seek with the phidgets)

    EDIT: alex beat me to the punch.. so.. yeah, what he said!

    -Fergs
    Last edited by lnxfergy; 04-29-2009 at 09:54 AM.

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