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  • Author Author: dubbie
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Tiny24hourMoBot #4 : The 24 hours is almost up

dubbie

After a late night last night with a test assembly of my Tiny Mobile Robot I wasn't quite so chipper this morning as I usually am. Still, I did have time to think about how to connect everything together so it would fit inside the shell. I used a bit of stripboard to make connections for the two 360 degree continuous rotation servo motors and the HC-SR04 ultrasonic rangefinder, plus power. There were surprisingly few connections once I had removed it from the proto-plugin board to a small stripboard and then connected the Arduino Nano using Dupont inter-connection wires.

 

The connections are as follows (Arduino to peripheral)

 

D3     servo motor 1

D4     servo motor 2

D5     Echo signal for HC-SR04

D6     Trigger signal for HC-SR04

 

All the other connections are just ground and power. Only a few connections. One of my original possible ideas had been to use a ATtiny85 for the controller for this but this would have required creating a programmer using an Uno and in the end I decided this was a complication too far for 24 hours. Still, I will create my ATtiny85 programmer soon and then I might revisit this mobile robot.

 

Once I had done all this connecting I was able to stuff it all inside the bodyshell. Regretfully I haven't yet managed to fit the batteries inside (there is enough space inside for 4xAAA batteries although not in a normal holder - if there was a smaller Arduino and fewer wires). Also I wasn't able to fit the batteries and the HC-SR04 ultrasonic rangefinder, yet. I think it would only require a couple more hours to do this so I might have a good.

 

The programme is pretty simple at present, all it does is to take one distance reading from the ultrasonic rangefinder and then moves to a while loop that just runs the servo motors from maximum forward speed all the way to zero and then to maximum backwards speed. With a bit more time then a much better programme could be produced.

 

digitalWrite(ustrigger, LOW);
delayMicroseconds(pretriggerdelay);
duration = 0;
distance = 0;

digitalWrite(ustrigger, HIGH);
delayMicroseconds(trigdelay);  
digitalWrite(ustrigger, LOW);
duration = pulseIn(usecho, HIGH);
distance = duration/onecmdelay;     // Conver to centimetres
Serial.println(distance);

 

while(1)
{ 
  for (leftspeed = start; leftspeed <= end; leftspeed++)
    {
      leftwheel.write(leftspeed); 
      rightwheel.write(180 - leftspeed);                                     
      delay(stepdelay);                      
    } /* for */


  for (leftspeed = end; leftspeed >= start; leftspeed--)
    {
      leftwheel.write(leftspeed);
      rightwheel.write(180 - leftspeed);                                                         
      delay(stepdelay);                      
    } /* for */
  } /* while */

 

Once put back together and the batteries added and turned on the Tiny24hourMobot springs into life. Well, maybe wombles about a bit anyway, see video below:

 

 

I did print a top to fit onto the body shell as well, but at present the wires get in the way so here it is without the batteries, or the wires or the HC-SR04 to show what it could have looked like. The first photograph shows the rather chaotic inside and the next one with the lid on showing a much more streamlined view.

 

image

 

image

 

I think this final photograph shows that if I could get it all to fit inside the shell I might have quite a nice looking mobile robot. I also think that with the experience

I now have I should be able to make it even smaller. The sensors need more thinking about though. The HC-SR04 is really too big so something much smaller is needed.

 

Dubbie

Parents Comment Children
  • in reply to Workshopshed

    Andy,

     

    I hadn't thought of using a boost converter. It would depend of which (the boost converter or another battery) took up the smallest volume. I'm sure there's an efficient approach somewhere that meets the small size requirement.

     

    Dubbie

  • in reply to dubbie

    Dubbie,

     

    I have had good success in building boost converters, driven by Li-Ion batteries.  The smallest converter was intended for a swarm robot, targeted to be under 1 cubic inch total.  The converter PCB is under 1 square inch (1.0 x 0.75) and includes both a charger and boost circuit, powered by a tiny LiPo battery (240mAh - off board, but about the same size).  More recently I developed a similar design (Walky the Biped Robot - Power pack ) based on a 14500 Li-Ion cell (1.1 x 2.5 - mostly due to the battery holder/cell size).  In general, I have fond that the higher energy density Li-Ion cells and a boost circuit are far smaller that the AA or AAA batteries that they replace (not to mention they are also lighter).

     

    Gene

  • in reply to genebren

    Gene,

     

    Looks like I'm going to have to investigate the use of a LiPo battery with a boost converter.

     

    Did you have any success with your 1 inch square swarm robot? I have been aiming for about 6 square inches and have not yet been able to manage that.

     

    Dubbie

  • in reply to dubbie

    Dubbie,

     

    I had shelved the nano robot swarm when I ran into difficulties in building a chassis for them (out of bent sheet metal), now with my increasing skills in 3D printing I really should get back to this project.  I have two of the three PCBs designed and tested (low level controller/battery maintenance and the motor controllers).  What I still need to work on is the high level controllers, which will allow be to modify the robots to be controlled (R/C) or autonomous (radio, I/R, accelerometer, multiple sensor based).

     

    The PCBs are so tiny, that they are very difficult to solder (0402 and smaller components and mostly leadless ICs).  I might need to pickup a small oven to flow solder versus hand soldering.  Just one of the many challenges.

     

    I look forward to seeing where you take your design in the future.

     

    Gene

  • in reply to genebren

    Gene,

     

    I have learnt a great deal about 3D printing whilest making my TinyMoBot and I have even managed to print some small wheels. It still surprises me what can be achieved with 3D printers when you start to think about the actual mechanical function required, rather than what you are already familiar with. I have shaved about 7 mm from the current width of 55 mm of TinyMoBot Version 1 just by redesigning the motor holding part and printing my own wheels, which now also have rubber tyres for better grip. This doesn't sound much but it now fits inside my target spray can lid. An advantage of making small mobile robots is that the print times are much shorter, only 11minutes for each wheel.

     

    I looked into trying a LiPo battery as I did have one I purchased for use with a MKR 1000 and it fits perfectly into the spray can top I am trying to use and a small boost converter would also fit nicely as well. Regretfully there doesn't seem enough room for the battery and the motors at the same time! Unfortunately my Arduino Nano does not fit either so I will have to get something smaller.

     

    I do not think I will ever be able to manage surface mount PCBs as I can barely see the old-fashioned pin-thro-hole ones I use now. I'll just have to wait until someone else makes the PCBs I want.

     

    Dubbie