I am interested in all aspects of mobile robots, including all the various methods of drive and steering. I mostly use direct drive DC motors usually continuous micro servo motors or micro DC motors as they are simple to control and provide easy directional control. Backwards and forwards are just running both motors in the same direction at the same speed, and turning is running both motors are different speeds and/or direction directions. Lately I have been looking at legged robots, although not getting very far but hey, I have plenty of time.
Recently I saw this Four Wheel Drive kit that uses chains to transfer the power from the motor to the wheels which looked interesting and was fortunate to be given one as a present- I only had to drop a few hints. Below is an overview of the kit of parts.
It is a simple kit mechanically but there were problems with construction. The instruction booklet is in an interesting variation of English and the drawings used to illustrate assembly look CAd generated but seem to have some strange perspective and it is not always clear how parts go together. I had to undo and redo a number of steps using my common sense to work out which part went where. The alternative is that I'm not very good at following instructions.
Although it is a relatively simple mechanism, the car has one small DC motor, a battery and an on/off switch and will only go forwards, it has two interesting features. First, it uses chains to transfer mechanical power to the front and rear axles simultaneously and with fixed axles this creates a four wheel drive system providing good traction. Secondly the axles can be placed off-centre from the wheels so that they are exocentric in motion and create a sort of leg-wheel movement, which is good for getting over obstacles, see below.
For such a low power DC motor the car has an impressive capability to overcome obstacles. The DC motor is specially designed to be low voltage and low current and it should be possible to power it from a solar cell rather than the single AA battery, so that is something for the future.
The chains are very interesting as they are simple plastic links that click into place. You have to take care as any sidewards pressure or motion easily snaps the sides off a link, as I soon discovered. Fortunately the kit comes with six extra links (I broke two) so I managed to create a working system.
Having now made the kit I plan to add a microcontroller and probably a sensor or two, to make it into a proper robot. I may also reconfigure the chain drive to make a more interesting vehicle/car.
Dubbie
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