Maxibug, Minibug, Microbug

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Click on the pictures to get a bigger image !



First I want to start with some theorie about how these bugs work.

I think it's kinda unique. Never found something like it on the Internet, and believe me:

I've seen a lot !


If you want to skip the theory part , click here to go to the tutorial.


The schematics of MAXIBUG


MAXIBUG is a bot with a supricingly good performance although it's build with common, not expensive components.

It is powered with two 3.3F Goldcaps. They can be charged in a few seconds. When they are charged, MAXIBUg gets "afraid" of light, and wanders of to go to play "in the dark". After a while, about 20 seconds (depending on the current used by the two motors ), the power has dropped, and it wants to "eat". It gets light attracted, and will turn and go to the light. When it gets there, it will recharge and still will be atrackted to the light until it reaches a trigger voltage , at which it gets "afraid"of the light again. This will go on all day until someone turns off the lightsource. While doing all this it also will backup when bumping into something.

Just imagine when there are a few of these bots....


How it works....    

In the schematics of Maxibug you see 6 diodes in serie with a 1 K resistor. Depending on the power supply voltage (voltage over the two 3.3 F Goldcaps), the measured voltage at point A will change. Look at this graf to see how it changes.



As you may know, the 74HC14 has 6 "schmitt triggers" inside it's housing. A schmitt trigger has a hysterese. That means that the voltage where it will trigger is at another voltage at where it will "fall back".

I've done some measurements at different voltages, and as you can see in this graf, also the "on" and "off" stages change.


When putting together these two measurements you get this graf.

Here you can see what will happen.

When charging the capasitors, the power supply voltage will rise. When it reaches about 8.3 Volt, then the schmitt trigger will turn "on". This will make our bot "afraid" of light.

Due to the power consumption of the two motors, the supply voltage will decrease. When it reaches 5.5 Volt, the black line ( measure point A) is getting lower then the green "off" line. This means that the schmitt trigger will turn "off". This will make our bot light seeking.

All this means that above a voltage of 8.3 it's afraid off light and below 5.5 V it gets lightseeking.

Did you get it ?

In short:

The output off the schmitt trigger depends on the supply voltage.



The change in output is visualised with two red LEDs. When the LEDs are burning, the bot is "afraid" of light. They are mounted as eyes off the bot, that's why I used two off them. One LED will do also, but doesn't look nice !

Because of the "on-off" output of the first schmitt trigger, the inputs for the LDRs will switch. That's why it gets light atracted -light afraid. This also means that you cannot use IR diodes (like SHF205). You have to use LDRs !

The rest of the schematics are normal used electronics, used by a lot of other designs (all over the world ). Nothing new.


I've noticed that it is neccesary to put a small C (10 nFwill do the job) connected to pin 7 and 14 of 74HC14 that is used measure the supply power. Mount it at the underside of the printed circuit as shown in the pictures and the printed circuit design.

I've made the design in such a way, that you don't need to etch a print, you can use uni. board (see pictures).


TUTORIAL Look at the components list for details    

In this picture you'll find all the components used to build this bot. The motors are small Mabuchi motors. Normaly used at 12 volt. In the front (right side) you see the guitar string. It is used for the bump detectors.



As can be seen in the first picture, I've made this bot on pieces of Uni. board .

Start with making the boards : the small one = 9 by 3 holes, and is used to give the two LDRs a higher place in the bot.

The big one is the chassis. Look at the printed circuit for more details.

You may have to changes it a bit to addept it to the motors you want to use.


Start with soldering in the components, as seen in this picture. Don't forget to put in the wire joints (there are 6 of them). They are red coloured in the printed circuit. As can be seen, the guitar feelers are mounted also. In the printed circuit design you 'll see four small holes between the two LEDs. Bend a piece of wire in a "U" form that is put in from the underside of the board. One "U" for the left feeler and one "U" for the right feeler. After soldering in, cut them at the topside so that they are about 3 mm (1/10 inch) long! The guitar feelers make contact with these "U" wires, when the bot is bumping into something. It's harder to explain than to build it.


When all the components are soldered in place start with the connecting on the underside of the board. Using a uni. board is simple but you must have some soldering experience, otherwise it will easely go wrong. Put a little blob of solder on the small copper "isle" you want to connect, then make them hot both, and put in some extra amount of solder. They should be connected now. Put a blob of solder on the next "isle" and make a solder connection between the new and the already made connections. Don't make it to hot ! Make sure not to make any mistakes, it's difficult to correct them. In the printed circuit design you'll find on the right side how you should connect the "isles".

Now it's time to put in the wires needed to connect the motors to the electronics. The print should look like this now!

So far, so good. Solder four leads to the underside of the small print. They should fit in the four holes in the chassis print , where the LDR connections are drawn. Put the four leads into thes holes and solder them. The small print should be about 8 mm ( 1/3 inch) above the chassis print. It has two reasons. The LDRs are sitting high in this bot, and it also functions as a extra joint for the motors.

Now make two motormountings. Bend them from a piece of brass (1.5 mm, 1/16 inch). The form to bend is depending on the motors you want to use. Look at the pictures to know how I solved this problem. The motors are mounted at an angle of 45.

Just another picture.

Look at mounting of the LDRs and the motors.

The bot is almost finished now. The only parts left are the two 3.3 F Goldcaps. They are soldered at the underside of the print. Make sure that you put them in the right pace, not confuse the + and - connctions.That would give you a lot of troubles when testing (charging).

The capasitor at the "behind" of this bot is bend somewhat down. This is the third point that stands on the ground. The 22 ohm resistor should also be soldered at the underside. In some pictures it is still mounted on top, but I changed that on my other bots. I've build already four of these bots. The 22 ohm resistor is used to slowly charge the goldcaps.


When all went well, the bot is almost finished now. The charge connections are to be mounted yet. I've made them from a piece of brass and a spring. Solder the - connection just in the hole in front of the hole where the to feelers are connected. The + connection is to be mounted at the underside, and should be made of a small spring. This is necesary so that both connections can make contact to the charging rings of the central charger. I'm still figuring out how to build this, but it will be ready soon.

For try outs just connect a 12 V power supply to the charge connectors. The first time you do this will take some time. The 22 ohm resistor will get hot. After a while one of the motors will start to turn. Keep charging until the LEDs are burning. The bot has "eaten" enough energy and wants to go away from the light. After about 20 seconds it turns and wants to go to the light (as mentioned earlier). To get an idea about the voltage during charging, connect a volt meter to the charge connectors.

By the way, when the bot gets light attracked, it will do this for about 30 seconds, just depending on the motors you're using. Just remember, all the power ( total cycle of 50 seconds) is just coming out of the two 3.3 F Goldcaps !

Other bots

Based on the same principle I've build other small bots. Just by using less diodes (4148) you can work with other, low current motors. The bot will do the same, but at a lower voltage.

Two others bots I've made on this principle are MINIBUG and MICROBUG.

MINIBUG works great, but is slower than MAXIBUG.

It does the job with only one Goldcap of 1 F/ 2.5 volt, it will work much longer, I've measured "afraid" times of more then 1 minute, and then it has several minutes to get to the light ( to recharge)!

I've used 3 diodes in serie for this bot. It gets "afraid"of light when the voltage increases above 3.9 volt. Below 2.4 volts it gets light atrackted.

Charging is done out of a 5 volt power supply, and will take as less as 5 seconds !



MICROBUG is freeformed. Electronically it works good, but the motors are turning to fast. I also think that the gravity point is to far to the back ( due to the 1F capasitor), and the motors have to less grip. Putting on some silicon tube on the motoraxles didn't improve much.

It is made with the same electronic components as used in MINIBUG. So 3 diodes and a 1F Goldcap. I've used 6 mm (1/4 inch) pager motors.

Believe me this bot is small, very small. Still have to do some more testings.

Impressed ? Just build one yourself, and be supriced about its behaviour !


Components list



Printed circuit. Click on it for bigger image.
  LDR 2
  1N4148 6
  74HC14 2
  470 ohm 1
  2M2 1
  1k 1
  22 ohm / 5 watt 1
  10 nF 1
  1 uF 1
  3.3 F Goldcap / 2.5 V 2
  guitar string (piece) 1
  small motors 2
red LED 2