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Topic: Just starting -feeling confident. a couple of questions (Read 1 time) previous topic - next topic

PeterH

#5
Dec 25, 2012, 12:53 am Last Edit: Dec 25, 2012, 12:56 am by PeterH Reason: 1
If you only need to move 360 degrees away from the starting point, I'd suggest using a fast servo with a 2:1 ratio between the servo output and the thing you want to drive, so 180 degrees on the servo gives you 360 degrees on your driven cylinder. Getting a servo with an adequate combination of torque and speed could be problematic, but I think you have a chance.

On the other hand if you need to move an arbitrary angle away from the starting point you have a much harder problem. Accelerating, decelerating and getting any sort of accuracy on the resting position is going to be quite challenging in that sort of timescale. In that case I'd try to come up with some sort of mechanical drive system that moved in increments of 60 degrees so that you just need to cycle it through the required number of steps and not try to interactively control the position and acceleration of the motor.
I only provide help via the forum - please do not contact me for private consultancy.

Botolph

I am really glad I asked the question  asall your comments are making me think.

PeterH:
1. It is always fixed positions (and small errors in position are ok). Thinking about it I could probably redesign the main component so that everything is accomplished in a 180 deg but it would add to the weight It may weight 280 gm. It would also reduce the rotation to 300 rpm.

2.
Quote
come up with some sort of mechanical drive system that moved in increments of 60 degrees
Not quite sure how to do this. Maybe something like an escapement on a clock, or a continuiously running motor with a flywheel, clutch and brake Though that does seem to start getting complex.

PaulS and JohnWasser:
I really appreciate your comments.

holmes4

So what is it you are really trying to do?. Don't talk about "time slicing" or FSM's and such. State your real goal, no buzz words, no star  trek style techno bablle just plain English. If you get rid of the rubbish that you don't understand and we think is boring then maybe we can help you.

Mark

Botolph


So what is it you are really trying to do?.


Thank you for your interest. The key bit I am trying to resolve, was described in my first post but I have copied it below,  and there have been a some really useful observations made here about the practicality of this
2. Can you suggest a motor or what do I need to consider. I need to be able to drive a motor to rotate in fixed 60 deg (or multiples thereof and forwards or backwards) but no more than 360 deg in one movement. A movement needs to be complete in about 0.1 second. The item it is driving is a hollow cylinder about 40mm in diameter and weighing about 120gm. I'm happy to pay for something reliable.


Don't talk about "time slicing" or FSM's and such. State your real goal, no buzz words, no star  trek style techno bablle just plain English. If you get rid of the rubbish that you don't understand and we think is boring then maybe we can help you.

Mark

On the subject of timeslicing this article explains it reasonably well http://en.wikipedia.org/wiki/Preemption_(computing)  I have used it commercially for writing operating systems and for things like aircraft simulators, missile guidence systems etc so implementing a timeslice process for my needs should be reasonably straightforward.  My commercial coding of these things finished about 30 years ago; the coding was mostly in machine code or we might write an assembler.

I should have spent more time learning about the electronics!

focalist

#9
Dec 26, 2012, 11:56 pm Last Edit: Dec 26, 2012, 11:59 pm by focalist Reason: 1
Personally, given the requirements, I would think that a reasonably gutsy stepper motor would be the easiest solution.  600 rpm isn't CRAZY fast, but it's not unreasonable either.  Sixty degrees is just 1/6 rotation... So that isn't a huge deal.  Reasonably high torque is easily done with a stepper, and they can be very fast....
When the testing is complete there will be... cake.

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