home  >  Baldur < Imp > ShadowLeg v2 6 June 2021

Imp - by David Buckley
October 2014
Imp is a 4 inch cube biped walking robot, controlled by a PicAxe40x2 with 32k external memory.
Imp is driven by four servos and powered by three AA cells.
The spurs front and rear are to aid it getting up if fallen over.
The red and green LEDs are for an indication of what Imp is thinking, they are on portB.
The forward facing clear LEDs are high power orange for illuminating obstacles, detected by the black shrouded photo-transistors next to them.
As can be seen in the Gallery at 2014-11-07 there are downward facing LEDs and photo-transistors for detecting table edges and black areas.
Long range sensing can be done by the Ultrasonic ranger module.
Imp can play sounds and Ring-tunes from its on-board speaker.
Imp can store hundreds of poses and command strings in its memory.
Imp can be instructed by commands from a Sony IR remote-control.
The full set of instructions can be sent serially as text over cable or a plug-in radio module.
Imp has on-board a full set of help files.

Back in the late '00s when Seattle Robotics Society had vibrant discussions on robotics, Randy Dumse, who founded New Micros Inc and created a line of Forth computer modules, had a friend at the local university(?) who suggested to Randy an Autonomous Biped Mini Sumo competition on rough ground! A Mini Sumo robot has to fit in an area 4 inches by 4 inches although it can unfold to be bigger once the bout has started, and was at the time quite popular. I think Randy's friend taught electrical engineering but it is certain he had never tried to build a biped robot - of any size - and probably had never built a robot or anything much in his life, otherwise he would have realised that with the currently available motors and electronics such a robot was virtually impossible to make at all let alone as a student project.

Anyway I bought some mini servos and created Bambino, a biped that would fit into a 4 inch square. It turned out that the PicAxe 20m2 controller I chose didn't have enough code space for routines which would enable it to be an autonomous Mini Sumo competitor although it would walk on slightly uneven ground.

In 2014 I decided to make a four servo biped to fit in a 4 inch square and called it Imp. I used a PicAxe 40x2 which has eight times the code space of the 20m2 and also has a lot more I/O pins. Imp will walk on uneven ground.

Imp has an expansion connector for portB of the PicAxe40x2 into which the Red/Green LED board is fitted.
At the rear are the 3.5mm jack socket for programming and the 1,3mm coax socket for external power.

Upgrade Log
The original servos as used on Bambino were HK15148 Analog Servo 17g / 2.5kg / 0.14s from Hobby-King. However the extra weight of Imp proved too much for the plastic gears and the servos were changed to JX-1171MG. But the two ankle servos were stiff and not as back-drivable as the HK15148, in June 2021 I selected two new JX-1171MG that were much looser, fitted them in the ankles and now Imp jumps right and left again
When the HK15148 failed, the JX-1171MG were the only ones I could find that were near enough the same size. Hobby King did have HK15148B with metal gears with the same case size as the HK15148 but even though they are specified for 4.8 and 6v, all the ones I tried running from 3AA cells died within a few seconds, running from 3v they seem fine. Hobby King refused to believe they were faulty - very annoying and very strange.