Hexbug Hack

Give your Hexbug a Real Brain!
Chapter 8 - Upgrades -

As I was finishing the first version of the Bug, lots of new possibilities and design branches where coming to mind. Incorporating all of them into one new design is possible, but would not be very practical. Instead, it seems that there will need to be some branching of the family tree.

The first upgrade will be to control/program the bug via a standard TV remote control. This will require an IR-Receiver module. After a fair amount of searching, the lowest possible operating voltage I could find was 2.5 volts for the Vishay TSOP34838. This poises a problem for the second upgrade- rechargeable batteries.

There are three types of batteries that can be used in the Bug:

1) LR44/GP76A alkaline- These are the standard, stock battery the bug comes with. Two supply a nominal 3 volts.

2) V40H NiMh, (nickel-metal hydride)- These come in a form factor which will fit in the battery compartment with a little modification to allow for their added height. Two supply a nominal 2.5 volts.

3) Li-Ion, (lithium-ion)- I have found no cell that will fit in the Bug’s battery compartment, but there are cells small enough to be tucked under the shell. A single cell will provide a nominal 3.7 volts.

Comparison of Batteries - Voltage vs. Capacity:

 

 

The alkaline cells will just be able to power the IR receiver module when the cells are 80% used up.

 

The NiMh cells will just be able to power the IR receiver module when fully charged, and has only about 36% of the alkaline cells’ capacity, so IR control isn’t practical. But this would be a good choice for a solar-recharging Bug. The small solar cells that would fit on the Bug would be a good match for these low capacity cells. And an added benefit would be that searching for a bright spot to recharge in would drive most of the Bug’s behavior. More frequent charging means more ‘activity’- what fun would a ‘self-recharging’ robot be if its batteries only needed charging once a month?

 

Only one Li-Ion cell would be needed due to its higher voltage, and it has almost twice the capacity of the stock alkaline cells. Even at the end of its capacity, its voltage will still operate the IR receiver module. The IR receiver could also be used as a means of finding a charging station.

 

Lining up the pro's and con's:

So the Bug will have three branches to its family tree-

 

The ‘A’ Bug: Stock alkaline battery, IR TV remote control

 

The ‘B’ Bug: A “Photovore”, it uses solar cells to recharge its NiMh batteries and is constantly looking for a ”bright spot”.

 

The ‘C’ Bug: Faster, more independent and a bit more aggressive, it uses a Li-Ion cell for extended range. The IR receiver module provides both TV remote control and helps it find its charging station.

 

All three Bugs can also have speed control thanks to the configuration of this H-bridge. Because there is an on/off control MOSFET for the bridge, it can be pulse width modulated (PWM) to regulate speed. A simple program should be able to cause it to creep very slowly, as if it’s trying to sneak away (timid ‘B’ Bug behavior), or like it’s stalking something (the more aggressive ‘C’ Bug). It could also slowly reduce its speed like its falling asleep.

1]The micro-robotic Hexbug is the result of collaboration between Ignition (Plano, TX; www.ignition.com), an industrial design and development firm, and Innovation First Inc. (Greenville, TX; www.innovationfirst.com), a product engineering company. RadioShack is the exclusive North American retailer of the Hexbug. Bandai, the leading toy manufacturer in Japan, also recently signed a deal for global distribution rights, with plans for other products to follow. “We had a rough idea for this product, but Ignition brought it to life,” says Joel Carter, VP of marketing at Innovation First. “They transformed our concept into a viable market-ready product and helped us to create an entirely new product category.”