RC Lawnmower

Discussion in 'The Projects Forum' started by johndavid400, Aug 11, 2009.

  1. johndavid400

    Thread Starter New Member

    Jun 28, 2009
    5
    0
    hello,
    I have been working on a project off and on for several months and thought I would share my progress.

    The idea is basically a battlebot with everyday usefulness. A metal frame with 2 wheelchair motors powered by a car battery, with a lawnmower attached to it. I know this has been done before, but I just wanted to try it myself.

    here is a web page that I made to track the project:
    http://rediculouslygoodlooking.com/site/lawnmower.html

    I have specifically been focusing on the H-bridge motor driver, building it from P/N channel mosfets and the code to translate a PPM servo signal from a typical R/C reciever into a PWM value that can drive the H-bridge.
    I will post some eagle files of the H-bridge if anyone is interested.

    Also, I am interested in coming up with a good PCB design for a high powered H-bridge (around 25amp or higher at 12v), so if anyone has any suggestions to the circuits I have already come up with, please feel free to suggest changes.
     
    Last edited: Aug 11, 2009
  2. NM2008

    Senior Member

    Feb 9, 2008
    135
    0
    johndavid400

    Kind of going off topic here, but, I too built a machine similar to those of Robot Wars/Battlebots and yours, last year.
    One hell of project, I may add with regard to labour and time!
    When planning it, I too thought of making it practical for everyday use, and thought of making it an RC mower.
    It was definitely going to be engine driven. (had to be)
    But with a horizontal shaft engine running the drive, it seemed impractical to add a vertical shaft engine for a blade,aswell. I also thought of running the blade and drive off the one engine, but sacrifices would have had to be made with respect to the drive speed/power and blade speed. Not good practice either.:confused: What now?

    So I decided to scrap the lawnmower idea.
    Went for a single engine drive, the engine puts out 7.5hp 4000rpm.
    The engine was purchased new , then stripped to bare block, many internal parts were replaced with strengthened parts.
    Basically it has been rebuilt to the same standard as the go karting race engines.
    And has 6degrees of advance.
    Got a bit carried away with the engine mods, paid off though!

    It will reach a speed max of 20mph which is rather quick for a 100kg lump of steel! :eek:

    It also has no problem pulling cars and other objects around the place.

    Just thought I would let you know, always interesting to see what other people build in their garages!

    Can send more images if interested.

    Regards NM

    BOT 1.jpg
     
  3. johndavid400

    Thread Starter New Member

    Jun 28, 2009
    5
    0
    that is an awesome bot... I stayed with electric motors for power b/c I am not experienced enough with small gas engines to feel confident building a bot around one just yet. Plus I thought the electric motors would be easier to control than gas... in my case, this was not true.

    But, I am planning on adding a stator or alternator of sorts to the output shaft of the mower and adding a charging circuit, so I won't have to charge the battery as often.

    I am very interested to see how you interfaced the r/c system to control the gas engines.
     
  4. NM2008

    Senior Member

    Feb 9, 2008
    135
    0
    johndavid400

    Theres for and against with the use of petrol engines,
    I could not or will never enter this machine into competition like BattleBots, first off it would not pass entry requirements and second it has a four stroke engine, which if flipped over means oil and petrol all over the place.
    And third, I put too much effort into it, to have it destroyed in five minutes.
    This was my first build of one of these and was based on robot wars machines, yet it was not built to compete with anything else. Just something to mess about with on a Sunday afternoon.
    Another disadvantage, its dam loud, similiar decibel levels to quad bike at full throttle, but I think it adds to the whole machine.:D

    Interfacing the engine was the easy part,
    for speed control basically its a 148 Futaba servo linked to the throttle on the carb.
    To start,
    switch on TX which in turn triggers a relay to, say switch on/un-ground the ignition coil.
    Pull recoil, then it will start.
    Turn the TX off and the engine will shut down, by switching the relay which grounds the coil ceasing the spark.

    Thats a basic idea of how I got the engine under control.
    There is also a failsafe circuit linked into whole machine, (a necessity for safety)
    Would not like to see this tearing off through the neighbourhood at 20mph stuck at full throttle.

    Regards NM

    Picture doesnt really show the servo connection,
    closest I had in photo collection.
    BOT 10.jpg
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Very classy bot! Welded chassis and all. :)

    Is it differential drive with a front castor? Or is it steered with a servo at the front and just uses a centrififugal clutch etc on the rear?
     
  6. NM2008

    Senior Member

    Feb 9, 2008
    135
    0
    THE RB.

    Thanks for the compliment!
    Yes, simple enough idea.
    It uses the diff from a lawn tractor, and has a custom built castor on the front.
    The castor wheel is actually a 10" go kart wheel.
    I had thought of using a servo for steering, but since I needed a diff anyway, it didnt really make sense to have a servo doing the same job as what the diff and castor will do together.
    Thanks for the interest.
    Regards NM
     
  7. pilko

    Senior Member

    Dec 8, 2008
    213
    20
    NM2008 -- How do you reverse it? Do you reverse the engine?
     
  8. NM2008

    Senior Member

    Feb 9, 2008
    135
    0
    pilko

    One of the disadvantages of using an engine and chain drive, no reverse.
    I had thought of using a motor linked in some way to the drive, which would give a low power reverse, I also though of using a gear mechanism, which would engage to a give reverse function.
    Both of these ideas, just sounded like something that would go wrong in the future thus causing a lot of bother for me.
    Also they would be tricky to build and add more weight.

    So it will spin on the spot, I have had no problems with this setup as of yet.
    As it will not be entering any fighting competitions, the lack of reverse doesnt really hinder its performance, although having said that, it would be nice to have!

    Thanks for the interest!
    Regards NM
     
  9. pilko

    Senior Member

    Dec 8, 2008
    213
    20
    The reason I asked about reverse was to determine what method if any you used. I built an electronic devise to reverse my snowmobile engine a few years ago.
     
  10. NM2008

    Senior Member

    Feb 9, 2008
    135
    0
    pilko.

    How may I ask did you do this?
    Did you actually reverse the direction of the output shaft on the engine, through a major timing adjustment?
    If so how did you do this?
    Does the engine have to be shut down then restated, to engage this reverse?

    Regards NM
     
  11. pilko

    Senior Member

    Dec 8, 2008
    213
    20
    You sense the speed, the direction and shaft angle. You kill the engine and when the speed reduces to around 100 rpm and when the shaft angle sensor detects you are at 40 degrees BTDS the ignition fires, kicking the motor into reverse. the system senses reversal and a new ignition angle is initiated to maintain reverse.
     
  12. NM2008

    Senior Member

    Feb 9, 2008
    135
    0
    pilko

    What type of engine do you have this device set up on?
    Regards NM
     
  13. pilko

    Senior Member

    Dec 8, 2008
    213
    20
    Bombardier, 340cc, 2 cycle with twin carbs.
     
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