"Starman" Vehicle

[jmoore]

Hi guys

As part of one of my uni assignments this semester, im trying to construct a 'starman' vehicle with my team. Basically we've come up with a whole heap of design ideas but nothing seems to be feasible, and i was wondering if you guys had any ideas/suggestions for this project

basically the project definition is as folows :

Starman Vehicle
The Starman is a fancy looking flat creature with 5 links in a single plane, giving it the look
of a star fish. Each link is motorized an can be moved clockwise or counter-clockwise.
The robot has a very simple mechanical structure with max. 5 motors (one for each leg - or
some simple arrangement) plus one motor for weight shifting outside the plane, to enable
sideways movements.

So basically it just has 5 legs and moves in a cartwheel type motion in a single plane, and with some sort of weight shift steering if possible.

Basically we have a limited budget (around about $250) and we cant seem to find any sort of feasible solution, we have been provided with whats known as an Eyebot JNR microcontroller, which i believe is based on a picaxe M40 or something (ill have to check on this when i get home) but basically the problem is the microcontroller only has 4 dedicated motor outputs, and only 2 servo outputs, but it also has a 10 pin digital output port as well. Essential we are stuck on
a) what sort of design to go for
b) how to link up the motors given the limited amount of ports

any suggestions would be much appreciated 

[paulstreats]

the 10 digital outputs can send signals to an h-bridge to control more motors if you need to.

Am i right in thinking that your star man will just sit there and spin around on its central axis?

do you have any designs you can upload for us to have a peek at

[Ro-Bot-X]

Build this one with 5 wheels:

http://www.societyofrobots.com/robot_omni_wheel.shtml

[jmoore]

to robot-x :

our vehicle must be capable of cart-wheel type motion i believe, not using omni directional wheels

to paulstreats:
i dont really have any designs at the moment because thats what im kind of stuck on, but i can give you an idea of what i have etc.

Also my lecturer mentioned something about i could daisy chain the servos to obtain control of all 5. Any more info on this?

[Gertlex]

Also my lecturer mentioned something about i could daisy chain the servos to obtain control of all 5. Any more info on this?

Not quite sure what daisy chain is supposed to mean, but you can certainly use two servos to control a motor.  I do it with my bluetooth RC car.  One motor controls polarity of the circuit, the other controls resistance with a potentiometer, and thus speed.

[paulstreats]

You could daisy chain the motors, but you would need to boost the signal current with an hbridge, Also this would result in  all of the motors always travelling at the same speed so it would just spin on its central axis.

 To get individual motor control you would definately need to get some hbridges attatched to the digital io ports you have,

 An easy example of an hbridge type circuit is here

http://robotroom.com/HBridge.html

 This uses a power mosfet driver to turn pulses from your io ports into power that you motor can be powered with.

plus one motor for weight shifting outside the plane, to enable
sideways movements.

Where are you planning on putting this, and how would it work? i.e. is it going to use a wheel to scoot along the ground, or are you going to mount it so it produces directional vibrations?

Also i can tell you that if the starman is spinning with the first five motors, and the last motor is set to move, you may expect the starman to say travel to the right in a straight line whilst spinning... This would likely be not the case. I imagine that it would move in a way that resembles a sine wave - and that is the best possible scenario.