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  • Author Author: dubbie
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RoboBobLet #2 : The Basic Chassis

dubbie
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Robots with Wheels

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I decided to use a fairly common chassis from feetechrc (www.feetechrc.com) FT-MC-003 available from several distributors as it provides the four continuous rotation servo motors as well as the wheels and rubber types, plus the chassis which all fit together nicely, albeit a bit fiddly. The photograph should show the chassis with the Arduino Nano mounted onto a piece of strip board to allow connectors to be used instead of soldering the motors. I used a Nano as it is low cost and has everything needed (at the moment anyway). Power is provided by the 4 x AA battery pack which also has an ON/OFF switch. I am only using the motors in full speed mode(forwards and backwards) at the moment. It takes a bit of fiddling around to get all the motors moving in the correct directions as none of the datasheets seem to show which direction the motors rotate for different pulse widths.

 

 

The YouTube video at https://www.youtube.com/watch?v=N_mAkRxrT_k&feature=youtu.be  shows the chassis just moving forwards and backwards for 1 second periods. When the chassis changes from backwards to forwards it rears up due to the momentum and the centre of gravity being nearer the back due to the battery pack position. It might be necessary to change the battery pack position if this becomes a problem. At the moment any problems will be overcome via software. There is some problem as can be seen in the YouTube video that after a few cycles it suddenly stops and then restarts. This isn't programmed so I think that this is a power dip caused by motor in-rush currents when changing direction that is resetting the Nano. I hope to fix this in the software otherwise a separate power pack for the Nano might be needed. At the end of the YouTube you can see the advantage of four wheel drive as the chassis climbs over my obstacle strewn desk without any problems.

 

Next a Bluetooth link will be used to provide manual control of the chassis hopefully via a smart phone.image

  • Nice start.

    It appears that you're feeding the battery pack straight to the 5v input on the Nano??

    I'm also thinking that you have a 5v Nano rather than the 3v3 versions.

     

    AA batteries are usually 1.5v nominally so 4 will be providing 6v, which some might consider in excess of the micro.

    You can help this by adding a diode in series to drop 0.6 v (meaning it is 5.4v)

    If you're using nicad batteries then these are nominally 1.2v which means you're only feeding it 4.8v.

     

    The 5v regulators really require 1.5v drop unless they are LDO (Low Drop Out) and these are 0.7v.

     

    SO as you can see there are some issues to resolve with battery packs.

     

    HOWEVER you might be able to overcome your resetting by adding the diode and a large capacitor across the supply line on the nano side of the diode.

    The more capacitance you can add the better, so 10,000uF or more will help.

    This should relieve the need for another power pack to run the nano.

     

    The other thing you might want to check is that both servos are rotating at the same speed ... no sense in fighting each other, that's simply adding more current drain.

     

    Cheers

    Mark

  • Nice rover, love the way it jumps.. Looking forward to more updates.

  • Cool little robot, look forward to the updates on the control.

     

    Kind regards

  • Great update on your robot project.  That robot really wanted to rearrange your workbench a bit.  Keep up the great work!

    Gene