Wall-e MkII - the tinkering begins...
June 12, 2014
As progress with Wall-e MkI (the test Wall-e) continues I can't help but start planning the 'proper' build, or the MkII :-)
Consider this a 'thinking-out-loud', rather than a definitive plan; I will document the second build in it's own Project.
At the start of this project I bought two identical toys; the first was always meant to be for butchering, for hacking, for experimenting. The second was to be the finished artical. The first attempt has gone, and is continuing to go, much better than expected and has made it a lot further than anticipated! Isaac (my son, and client ha ha) has found Wall-e fascinating to watch and follow, even though arms and head movement or object avoidance has not been achieved.
MkI is currently in pieces being fixed (a motor has freed itself from it's gluey shackles to roam free inside Wall-e, the swine!).
While I am overjoyed at the progress both myself and Wall-e have made over the course of this project I think I have rethought the original build enough to start tentatively piecing together the much improved version...
The focus of this segment of redesigning is the internal 'block' of components; firming up the good things of the project, ironing out the bad things, and making it ready for future improvements.
- The Aduino Core - Uno to Nano
The MkI is based on an Arduino Uno with attached Adafruit motorshield. It is designed to run 4 motors and 2 servos, easy to use, has its own simple library etc, great to get started with.
My project, however, is evolving to require only 2 motors, yet 3 servos. For this application I feel the motorshield would be inefficient, taking too many pins to functions that aren't going to be used, and limiting my ability to expand.
The MkII will potentially be using an Arduino Nano, a L298n-based motor driver for the 2 motors and I will fashion my own Nano breakout perfboard to cater for servo, LED, sound and bluetooth connections etc. One day I may even attempt creating my own breakout board with my own integrated motor driver, but that is for when my pins are finalised and is a completely different project!
Advantages - smaller, better use of pins, more customisable options
Disadvantages - TBC
- Motor gearing and Placement
When the MkI was being modded for motors the plan was to use normal, ungeared motors. These motors would be too chunky to fit nicely under Wall-e without being exposed, plus would need gearing to reduce speed/improve torque etc.
I then found some really small geared motors... This has resulted in geared gears ha ha, and while the torque is bordering on the monumental the speed is most certainly not.
The MkII plan is to mount these little motors underneath, going directly to the track wheel; if they don't fit in the area for them some PVC tubing will be used to cover them.
Advantages - better speed, more space inside Wall-e's body, less gearing=less things to go wrong!
Disadvantages - less torque, potential modding required to hide the arse-end of motors if they don't fit nicely
The MkI is currently running from 2 paralleled 9V batteries, shoe-horned alongside the Uno. They do the job and last long enough, however aren't rechargable and require taking Wall-e apart to replace.
I bought 4 x 3.7v 5000mAh batteries to create a 14.4v pack - the plan was to couple that with a balanced recharging circuit pilfered from another device and stick it in instead. MkI doesn't have the space for the size of batteries however - insert sad face here.
MkII however, with its motor relocation and smaller internals, will have space under the Nano/motor driver combo. Hurrah!
One thing to factor in is the requirement of voltage regulators; one down to 12v for the motor driver, one down to 5v for the arduino. The motorshield had been regulating the power for the Arduino in MkI.
Advantages - long lasting, internal, rechargable, more than enough power to allow motors to run at optimal voltage,
Disadvantage - additional regulators required, recharging circuit to be considered
- Arms/Head movement (FINALLY!!)
I have just received 4 servos to play with, and if my new, space-saving internal design allows, I'll be able to add the arm and head control i dreamed of at the beginning of this project. Hurrah!
- Other bits and bobs
Other things that i would like to do or need to sort out:
MicroUSB port on front/back of body; if possible connect to a hacked microUSB cable to the Arduino as well as to the recharging circuit. One can dream!
I have attached a pic of the potential block taking shape - work will start soon on the breakout of the nano pins. Please comment if you have any tips or input :-)
Thanks for reading!
|Sizing up on Wall-e base||1.32 MB|