South Pointing Chariot (Electronic)

Hi, I need to design and build a "South Pointing Chariot" not mechanically, but electronically.

What is a South Pointing Chariot?:
The chariot is a two-wheeled vehicle upon which is a pointing figure that always point in the same direction (of the compass) as the chariot moves.
South Pointing Chariot - Wikipedia, the free encyclopedia

Requirements:
The figure on top of the chariot should always point to the same direction of the compass regardless of the chariot's motion.

The pointing direction is read from the PC.

As the chariot moves, the distance that the wheel(s) travel should be collected.

The trajectory (direction and distance) that the chariot follows
is recorded in the PC.

Hardware must be on stripboard or PCB.

I know how to build this mechanically, but not electronically. I need ideas on how to implement this electronically.

Any assistance or ideas would be greatly appreciated.

JP.

Hints.

Place a sensor on each wheel that counts how far the wheel has turned.

As long as the distance traveled by each wheel is equal the heading has not changed. As a given wheel travels less then its companion the heading changes in the direction of that wheel.

Does that help.

Sounds like a College assignment.?

As you may know the Chinese invented the 'mechanical' version two thousand years ago...

South Pointing Chariot - Wikipedia, the free encyclopedia

EDIT:
Interesting version:
Dont let Bill [BRE] see this or he will insert a PIC into its differential orifice.!

**broken link removed**

you can almost do it with optos linked to a stepper motor, but it is hard to get the difference in frequency... and I do not have time to sit and think it through.

Perhaps just linked directly, each pulse driving it forward for one wheel and each driving it backward for the other, with some logic to control direction for the wheels going backwards. The you still need the right ration to the optos and stepper, but it will be electronic and lack a micro.

Obviously, it would be easier with a micro to do all the ratios in math, allowing freedom in the mechanical structure.

Dan

Stepper motor, digital compass module and... MCU

blueroomelectronics said:

Stepper motor, digital compass module and... MCU

Click to expand...

But the requirement was to be based on wheel motion

Ahh, hall effects sensors or a gray code wheel encoder. Why are we doing homework assignments?

I just wanted to start the OP thinking.

He did not say if the wheels where driven.

Thnx for the ideas so far, btw I have to build it electronically. Isn't the motor a mechanical device?

Also, what is an optos/stepper?

blueroomelectronics said:

Ahh, hall effects sensors or a gray code wheel encoder. Why are we doing homework assignments?

Click to expand...

I don't know, we usually scoff at them...I guess because this is an intriguing one, as opposed to the run of the mill "how do you calculate current X in circuit Y" stuff.

Dan

3v0 said:

I just wanted to start the OP thinking.

He did not say if the wheels where driven.

Click to expand...

Do you mean as in computer controlled or manually moving it?

To my knowledge, manually driven.

I'll confirm this soon.

jon_pops said:

Thnx for the ideas so far, btw I have to build it electronically. Isn't the motor a mechanical device?

Also, what is an optos/stepper?

Click to expand...

One thing that I do not like is when people ask for help and then fail to answer the questions put to them.

Maybe you failed to understand the first time. Is this chariot self powered or is it pulled or pushed by some external force. The orignal was pulled/pushed so I expect this one should be to. That would mean no motors on the wheels. Just sensors.


FWIW a motor is both electric/electronic and mechanical.

The reason I put up a fuss about homework assignments is the entire point of these assignments is to get the student thinking. We're not doing them any favors by doing the work for them, unless the course is in management.
When a student posts just the assignment and adds no ideas of their own then they've not done their homework.

jon_pops said:

Thnx for the ideas so far, btw I have to build it electronically. Isn't the motor a mechanical device?

Also, what is an optos/stepper?

Click to expand...

Optical sensor, detects wheel direction and speed. Stepper motor, used in various positioning systems such as printers, and robots.

Dan

3v0 said:

One thing that I do not like is when people ask for help and then fail to answer the questions put to them.

Click to expand...

hi,
Failing to answer a question is high on my list of irritations.

I have had a few threads recently where I have asked a question and all I get back is another question
or complete change of direction in the OP's requirement.

jon_pops said:

Do you mean as in computer controlled or manually moving it?

To my knowledge, manually driven.

I'll confirm this soon.

Click to expand...

neither, a trailer with a pointer that always points the same direction regardless of path traversed by the wheels. Check his link, quite amusing mechy trick from the ancient Chinese.

Dan

Ubergeek63 said:

neither, a trailer with a pointer that always points the same direction regardless of path traversed by the wheels. Check his link, quite amusing mechy trick from the ancient Chinese.

Dan

Click to expand...

No linky , I thinky,

ericgibbs said:

No linky , I thinky,

Click to expand...

I see one in the very first post, to wikipedia.

Dan

Hi jon_pops,

An interesting puzzle.

If i were to do this, as a test, or demo piece, the i think i would start by destroying an old wheel mouse.
The way i see it is very similar to how 3vO says: ...
******
As long as the distance travelled by each wheel is equal the heading has not changed.
As a given wheel travels less then its companion the heading changes in the direction of that wheel.
******
But i would say it the other way about, that as a given wheel travels more then the heading changes away from that wheel.

So if a wheel stops turning,
and the unit continues to travel,
the wheel still moving will describe a circle.

The sensor on the moving wheel in this case should cause the indicator to revolve one counter revolution, as the unit travels around a circle.
The moving wheel may do two or three revolutions and maybe also part revolutions to complete its circle, the sensor-to-indicator action has to produce one counter-wise revolution for each full turn of the unit.

And the same for the other wheel.

Thing is, if this is digital, the steps would have to be very very small because errors will be cumulative, and also multiplied by distance travelled.
But i suppose that accuracy is not the main reason for the exercise.

I am trying to think of some non-digital way to do this, unsuccessfully so far. There may not be a non-digital way to do this electronically.

Best of luck with it, John

how about a largish actual compass, out of sight in the machine, with a ring of sensors round the edge (say optical, or inductive) to sense the pointer postion. Cheating a bit, but always accurate ;-).