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  • Author Author: dubbie
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Tiny24hourMoBot #3 : 13 hours have passed

dubbie
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A Question of Scale

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It is now over half way through the 24 hours for my Tiny Mobile Robot and I have a sort of working prototype.

 

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I 3D printed a cylinder slightly wider than the widest part of the two motors which also had a mounting bar at the bottom. I very carefully used self-tapping screws to fix the motor unit to the mounting bar. It is stable but could easily break if knocked - so hopefully I will not knock it. I have programmed the Arduino Nano to simply move both wheels together so that the whole mobile robot moves backwards and forwards in a straight line as I need repeatability while I stuff everything inside the cylinder. As it is a mobile robot it needed to have some sort of sensor and as I had a HC-SR04 ultrasonic distance sensor I decided to use that. The HC-SR04 is a simple to use sensor as all you need to do is to add power, a trigger signal of at least 10 microseconds length and then measure the length in time of the echo pulse detected. Dividing the length of the detected echo by 58 converts time into distance in centimetres. At the moment it is not making use of the data from the sensor but it is all working, see below:

 

 

There is a great deal of wheel slip as the batteries are quite heavy and it really needs elastic bands for tyres, but unfortunately I do not have any. I will see about using AAA instead of AA batteries later and see about fitting everything into the cylinder. I have also 3D printed a top for the cylinder so that I should be able to mount the ultrasonic rangefinder to that. I don't think it is going to look as good as I had hoped, nor is it going to be as tiny as I originally planned. Maybe I should call it the not quite so tiny mobile robot.

 

Well, it is late now so I'm going to bed soon. There is still time for a couple of hours work tomorrow morning before my 24 hours is up.

 

Dubbie

  • in reply to jw0752

    John,

     

    I agree, I'm a bit fan of the 'I'm thinking about it' approach. It was while I was in bed last night that I thought of a smallish method of connecting all the wires together. I may well have thought of it when I started again this morning but it did mean I was ready to go straight away in the remaining time.

     

    Dubbie

  • in reply to nobble

    Elliot,

     

    Yes I do like the smaller robots, more manageable at home. I do sort of enjoy the difficulties that trying to go small introduce as well, which are really not that related to functionality. The effort involved in design and construction seems to increase exponentially once a certain smallness is reached. I was surprised by how large my body shell had to be made just because the wheels had to be so large due to the distance from the motor axle to the edge of the motor body. It would probably be a lot easier if the motors could have a gearbox that brought out the wheel axle at 90 degrees to the motor axis.

     

    Dubbie

  • in reply to genebren

    Gene,

     

    I did think about O rings, a lot, but mainly in frustration as I don't have any. I think they might be something I might need to buy. I would then have to work out how to design the wheels in TinkerCAD to make the grove for them to fit into. I'm not sure how difficult that might be.

     

    Dubbie

  • in reply to dubbie

    It is too good a project to stop at 24 hours :-)  I have been interested in mini robot swarms for some time and look forward to seeing what you come up with.

  • Often when working on a project for an extended period of time I will stop and find a point at which I can put it aside. I usually can't put it aside mentally even if I physically walk away from it. While I am away I continue to analyse and go over ideas and problems in my head. When I return to actually working on the project I almost always have an improved approach and the break has been a beneficial thing. It looks like you have a really nice project well on its way to completion.

     

    John