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106  Community / Website and Forum / Re: Scope on: January 16, 2013, 01:43:08 pm
Thanks smiley

The documentation is generally elegant and clean although not always consistent; but a great job! smiley-grin  (no clapping smilies)
107  Using Arduino / Motors, Mechanics, and Power / Re: Monitoring and Charging Multiple Batteries on: January 16, 2013, 09:06:39 am
Does the laptop not have a built in charger? Thus you will have nothing to do there, other than wait and something like 19.5 V to play with once charged?

The robot will not be moving while tethered, so that is easy. You know how long it takes to charge the laptop or monitor the colour of the charge lamp etc. So do that first.

disconnect the motor power, Then switch the supply to your bat charger. LiPo need special chargers, as have you have found! (and can be dangerous!)

Basically you need to check the battery voltage from time to time until it reaches the required battery voltage or until your specific charger, gives a signal that float mode has been reached (etc). This may be an LED, and then either inform you (break tether), or else switch (bat) power back to motors and trundle off.
108  Using Arduino / Motors, Mechanics, and Power / Re: enabling stepper to turn once every 24 hr on: January 16, 2013, 08:56:57 am
Following on from SouthernAtHeart, many RTCs have a square wave output, often down to 1 second. count off the number of ticks required to give the correct step interval. Call your step and go back to watching the clock.
Depending on what else you need to do, you may have to employ interrupts to allow you to do some useful work while watching the ticks.

Have fun smiley
109  Using Arduino / Motors, Mechanics, and Power / Re: First Stepper Motor Project - guidance requested on: January 16, 2013, 08:52:28 am
You will need a LOT of power to run those devices. That will be an expensive Stepper & PSU. Try fitting a pully where the handle goes, wrap a cord around it and hang a weight off of it - it needs to handle worse case.

Your arm is very strong. Making robot arms to move 5kg loads about ain't cheap! You do it without thinking!

I would tend to use a cheap 12 DC motor with a reduction grear-box, and a couple of relays, or employ a small child to peel my spuds.

Check out ebay for say 12V 30 RPM - which is probably too fast smiley-wink
110  Using Arduino / Motors, Mechanics, and Power / Re: MOSFET for DC motors on: January 16, 2013, 08:37:18 am
Use a transistor by all means, a low/highside drive would be better. You want a fast level change.

Don't forget that low on resistance only occurs when the device is fully driven. Switching provides a lot of time for when the device is not fully driven (rise & fall time) so a large potential for over heating.

If you can get the specs for the motor it will make choosing a FET easier, however, although robust when properly specified, they are easy to pop. So always over-specify (they are so cheap!) (I buy them by the tube) and use a heat sink. Try running for a moment and see if you notice a temperature rise.

Don't forget a (fast) fly-back diode!

And once again, read the specs and the manufacturers recommendations.
111  Using Arduino / General Electronics / Re: Resinator v Crystal on: January 15, 2013, 05:48:35 pm
As I remember mu metal was used (as said above) as a magnetic shield around CRTs in scopes etc. Talking of which, rather than guess, get a decent scope, it'll pay for itself over and over if you learn how to use it.

And you can metallize the inside of plastic cases smiley-wink Check out your mobile phone.

If you look at the data sheet for any device that requires a high frequency clock, you will find very specific information about ground planes, guard rings, shielding etc.

If you are producing a commercial product, you have to comply with FCC rules! smiley-wink
112  Community / Website and Forum / Re: Would it be possible to have tapatalk support? on: January 15, 2013, 05:32:07 pm
Does tapatalk allow you to post while driving or crossing roads?  smiley-cry
113  Community / Website and Forum / Scope on: January 15, 2013, 05:27:40 pm
Couldn't find a specific place to post this.

in the reference for Variable Scope, it is stated...

Quote
Variables in the C programming language, which Arduino uses, have a property called scope. This is in contrast to languages such as BASIC where every variable is a global variable.

This is not strictly true for all BASICs and my be misleading/confusing to some readers. Perhaps the text should be altered in light of this?

e.g. Visual Basic, XBasic, Dark Basic & Free Basic to name just a few all have forms of scoping (although they may or may not be directly analogous with C scoping).

Any thoughts?


114  Using Arduino / Motors, Mechanics, and Power / Re: Tansistor help to power motors on: January 14, 2013, 08:52:23 am
I suspect that you are pulling way too much current for that poor little tranny and no heat sink.

To run a car motor you should be using (a bank) of MosFETs They will exhibit ultra low on resistance, but will still need heat sinks.

Although a little harder to drive, they are well worth the effort - you will probably find that the fixed PWM frequency is not best suited to your motor, so try writing your own dedicated PWM.

And also a soft start - That will be fun to get right for your motor too smiley-wink

"what you can do" and "doing it right" ain't always the same! smiley-wink
115  Using Arduino / Motors, Mechanics, and Power / Re: Backlash problem about step motors on: January 14, 2013, 08:34:59 am
Getting hot is 'normal' (you are locking it in position by energizing the coils). is it (much) hotter than the other motor?

If you grab the output shaft and twist, does it move/rock, if so, is the other motor just the same? (could just be low torque, so comparative force to move the shaft)

If the motors DO behave differently (but the same motor type), is it possible to reverse the motor electrical drives - you may need to disconnect the motor output to prevent damage.

If the problem moves, you have an electrical/drive/software problem.

If not, then you have a mechanical problem. Disassembly of big motors is quite easy, you may find that the field windings have broken loose and are able to rotate, although that may be accompanied by a lot of noise while in motion. It may also be a single coil that is defective. This may not be noticed if positioning is via some form of encoder rather than absolute stepping, only when holding would a problem manifest itself.
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