The Soap Box Cart



First see the video
of the WiFi controlled cart.

Why build the cart?
The project provided an opportunity to experiment with the interface between hardware and software and to compare the differences between programming personal computing systems and embedded micro-processors. These experiments were conducted in the context of a very flexible steering system and the virtually unlimited control range afforded by WiFi and Internet Protocol (IP). The original plan was to construct one of the two-wheeled robots very popular with hobbyists but it was eventually decided that the resulting vehicle would be of very limited application and capable only of traversing smooth surfaces. However, note that the current design can be viewed as the drive of a two-wheeled robot coupled with a trailer by means of a 360 degree pivot. A slip ring capsule within the pivot enables the heavy battery and bulky control system to be separated from the drive and located on the trailer thereby distributing weight evenly between the four wheels.

The lively history of soap box carts.
This is Oor Wullie, a strip cartoon character in the D.C. Thomson newspaper The Sunday Post.

Wullie is riding on an improvised gravity propelled vehicle which in his part of the world is called a 'bogie'; possibly because its pivoted steering mechanism faintly resembles the bogie wheel assemblies on some old steam locomotives. In other parts of the world such improvised vehicles are variously called kart, kartie, soap box cart, bodge, trolley and pram trolley; the latter because the wheels of the vehicle are traditionally obtained from unwanted perambulators. During the first 65 years of the 20th century many 8 – 12 year old boys (and tomboys!) had such carts, usually built by dads or elder brothers from old pram wheels, scrap wood and, typically, soap boxes. They cost nothing and gave the children (and their fathers!) a lot of fun. Later ad hoc cart building declined probably because of the availability of more sophisticated toys (like skate boards) and the shortage of proper pram wheels in these days of the buggy. However, in recent years a more organized manifestation has emerged in the form of rallies and events where the soap box cart thrives in an ethos of do-it-yourself innovation. Evidence of this is clearly demonstrated by searching the Web for images using such phrases a ‘soap box Derby’ and ‘soap box cart’. Finally, please remember that a full size ride-on cart is dangerous to both the rider and third parties. The rider should wear a helmet and protective clothing. Effective brakes are essential and carts should only be used on gentle slopes well away from traffic and under the supervision of adults.

Safety and Technical Details of this WiFi Cart.
Readers may, at their own risk, build carts based upon the outline information given in these pages and in the video but, for administrative and safety reasons, all the precise specifications are not offered here. Even scale models can cause damage so potential builders should develop their own detailed plans and pay close attention to safety at every stage of building hardware and software. In particular builders should ensure from the start that their design will incorporate automatic and effective braking and shut-down when their cart loses connection with its controller. Builders should also study the safe procedures for charging, discharging and storage of lithium polymer batteries. If in any doubt then consult an appropriate professional engineer and/or software developer.

See some detailed drawings here.

See a wiring diagram here.