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    Originally Posted by gimp
    I'm thinking of creating my own joysticks: Pot, spring, and stick.
    Never make something yourself when the same part is made on a factory line somewhere else. There is no way you can make it for less.

    Only make stuff that can't be bought. and Joysticks don't count.

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    • gimp agrees : Yes, I think I covered that in the second half of my post.
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    All motorized systems that are not kept in a cage, should have a master power watch-dog that cuts power to everything if; an emergency stop (E-Stop) button is pressed or any one of the involved processors fail to pet the dog. This can be somewhat less rigorous if a small child would be capable of physically restraining whatever mechanisms the motor engages and the peak operating inertia is low enough that injury would not result from accidental or deliberate contact.

    Failure to supply an obvious E-Stop and/or fail-safe design incurs both civil and criminal liability. Seek council. The design you have elucidated thus far would not be fail-safe and depending on the torque and speed of the motor, plus the composition of the propeller, could be dangerous. Most motor controllers have provisions for fail-safe designs and/or E-Stop input. E-Stops generally have negative logic by the way.
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    Originally Posted by jwdonahue
    Seek council. The design you have elucidated thus far would not be fail-safe and depending on the torque and speed of the motor, plus the composition of the propeller, could be dangerous.
    Its a toy. It "could" be dangerous, perhaps, if certain specifics are met, which are unclear from the specs that @gimp has posted so far.

    Granted, a big "off" switch is probably a good idea, but threatening lawyers is a bit much.
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    Originally Posted by fishoprecords
    Granted, a big "off" switch is probably a good idea, but threatening lawyers is a bit much.
    Quit taking everything I say so personally. I did not threaten anybody with lawyers. It is my responsibility as an engineer to point out such matters when they appear to have been ignored. Poorly designed toys have been known to kill and maim adults and children alike.

    Since this forum is new and the topic of liability had not been brought up yet, I thought this was a good place to point it out, particularly since the design in question would not be fail-safe. Safety should always be a primary concern for both hobbyist and professionals alike. There's simply no excuse for ignoring it and many a hobbyist and engineer has been brought up on criminal charges for such negligence. EDIT: assuming they survived their own negligence.
    Last edited by jwdonahue; October 28th, 2009 at 07:12 PM.
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    Originally Posted by jwdonahue
    Quit taking everything I say so personally.
    So learn to write clearly.

    You have been in this section of the forum for a few hours, stomping like a bull in a china shop. Lighten up.

    Comments on this post

    • jwdonahue disagrees : I think I have been clear. And I have every right to post in this forum as you do.
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    Originally Posted by jwdonahue
    There's simply no excuse for ignoring it and many a hobbyist and engineer has been brought up on criminal charges for such negligence.
    Got a citation of a toy boat where the builder was found liable?
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    Not off hand, but I don't really need one to justify my post. Can you prove he wouldn't be liable? No, of course not. As I always suggest when it comes to legal matters; seek counsel, and when it comes to matters of engineering, think safety.
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    Originally Posted by fishoptrecords
    ... stomping like a bull in a china shop
    Ya, it does seem that someone's ego is a bit fragile. I apologize if I have offended you. You're just going to have to get used to the idea that I will be active in this forum.
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    I'm a little confused as to how I haven't made an "E-stop"? If the receiver gets no input for more than half a second it goes dead. The default joystick position is dead. A small motor running at 0.6 A average, 1.2 peak, with a propellor attached can't hurt your fingers.

    [Can we not bicker? ]
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    Originally Posted by jwdonahue
    I apologize if I have offended you. You're just going to have to get used to the idea that I will be active in this forum.
    From the beginning, you have insulted me and @gimp. From the first line of your first posting, you started out bad, and got worse. I have no idea why.Unless you start posting entries that have useful content and don't start off with insults, you will quickly join Arty in my ignore list.

    Embedded programming is fun. Its easy once you make the jump into it. It can be profitable.

    You have no citations on the liability issues, yet you expect people to respect your posting. Just a hint: there are very few postings on DevShed from licensed Professional Engineers. Most of the folks here deal with software, and while there are liability issues in software, its at best a specialty.

    Describe your own projects in a thread. Or help @gimp with his.
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    The death, as you describe it, is dependent on your code actually doing what it's supposed to. Fail-safe, means it stops working the instant your code or other part of your system goes off into the weeds. That is what watch-dogs are for. If you don't pet the dog, the thing cuts the power to your motors and all the related controllers require to operate. A proper E-Stop is usually AND'd with the watch-dog output that holds the power on. If either of them goes low, the power goes off.

    Originally Posted by gimp
    with a propellor attached can't hurt your fingers
    Then you have nothing to worry about if the boat can't go fast enough to cause any harm either. As I said in my post; "This can be somewhat less rigorous if a small child would be capable of physically restraining whatever mechanisms the motor engages and the peak operating inertia is low enough that injury would not result from accidental or deliberate contact". Seems simple enough. I said what I was obligated to say, you've taken that and drawn your own conclusion, nothing for us to bicker about
    Last edited by jwdonahue; October 28th, 2009 at 07:07 PM.
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    By 'we' I meant the, um, extended we that doesn't apply to me. I've mountains of material to learn and I accept harsh criticism just fine. I sometimes succumb to the knee-jerk "**** you" but I'll usually realize my faux pas and apologize.

    Because the motor controller is hooked up to the arduino, the only way it could go wrong is if the arduino somehow jammed a positive voltage on a signal line... let's be honest here, I could make a redundant system to fix that but I'm poor.

    Unlike my last project (which was my first major one), this one is well thought-out and well-structured.


    (And as a side-note: You haven't had too much interaction with me but if you know my temperament you know that I eschew most personal safety as luxury. If it can mess someone else I gotta fix that, if I get hurt I don't care - it's all part of the learning process.)
    Last edited by gimp; October 28th, 2009 at 09:59 PM.
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    So just to inject some more reality here, but a bit more along technical lines...

    Originally Posted by gimp
    A small motor running at 0.6 A average, 1.2 peak,...
    The statement implies the motor is not strong enough to cause injury. I actually believe you, but you haven't really supplied sufficient information for anyone to judge for themselves. For power or strength, motors are generally rated in watts or horsepower and generally include a peak and/or starting torque rating as well. You can have a motor that is capable of doing a lot of work, but if it's starting torque can't overcome the inertia of a stopped system, that system would have an over-all power output of zero and it's motor devolves into a resistive heating element commonly referred to as a dead load.

    The starting and peak torque ratings are probably more relevant to the safety issue regarding the propeller (assuming it has low mass and no hard sharp edges) the power rating is probably more relevant to the safety issue of peak inertia of the whole boat. Once you have sufficient torque to turn the propeller, output power comes into play. The higher the output power, the faster the boat will go and the faster it moves, the higher it's momentum; velocity combines with mass to exert force when the boat collides with something or someone.

    For the purposes of rating electric motors, 1 horsepower is equivalent to 746 Watts. Your motor could be a 1 horsepower motor at 1.2A if:

    Code:
    1.2 * V  = 746
    746/1.2  = V
             = 621.7V
    Now, one horsepower can move roughly 550 pounds 1 foot per second, but your boat probably doesn't weigh that much and you probably don't have a 1.2A @ 0.6KV power source, but I just wanted to introduce some concepts and give you a handle on the scale of the forces involved.

    1.2A * 9V = 10.8W

    That's roughly 1/69th HP. 1/69th of 550 pounds is 7.97 pounds. There's a design point for you; if you want your boat to travel on the order of 1 ft/s using a 10.8 W motor, you'll have to come in at somewhat less than 7.97 pounds (displacing water can be such a drag).

    So based on the numbers you have supplied and a more or less reasonable assumption of available voltage, I can more or less predict a range of practical masses and velocities that might be involved and conclude that a practical model boat, driven by such a motor, could actually attain velocities sufficient to cause some harm, but probably can't go so fast that a person couldn't get out of its way fairly easily, given sufficient warning of its proximity. Of course, that assumes that the boat would continue along a straight line as well.
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    I'll be testing my wireless communication between arduinos next week. The combined cost is a lot ($20 cable, two modules at around $25 and two boards at around $10) but soldering them is a breeze and so is hooking them up to the computer.

    For windows, follow the instructions on the ladyada site. For linux:
    Download, install minicom
    minicom -s
    Set baud rate to 9600 8N1
    Set the port to the right thing (for me it was /dev/ttyUSB0
    Exit (not from minicom, just exit, it's an option)

    Then you type in
    Code:
    +++[returns OK]
    AT
    [returns OK]
    ATBD
    [returns 3]
    ATBD 4
    [returns OK]
    ATBD
    [returns 4]
    ATWR
    [returns OK // this just wrote the settings]
    Restart the module by ending the call (control A, then Z, then H) and by unplugging it and plugging it back in
    Set it up to be 19200 8N1
    Repeat above, except set it back to 3 for 9600 or anything else you want, and you're done!

    (This took me a while to figure out.)
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  28. #45
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    The motor control I soldered-a, she no-a work-a.

    50/50 I burnt out a chip soldering (no IC holders and one got really hot - oops) or I just did something else wrong.

    I think I'll just buy a motor controller instead. Waste of money but life ain't fair. I'll play with wireless in the meanwhile.
    Chat Server Project & Tutorial | WiFi-remote-control sailboat (building) | Joke Thread
    “Rational thinkers deplore the excesses of democracy; it abuses the individual and elevates the mob. The death of Socrates was its finest fruit.”
    Use XXX in a comment to flag something that is bogus but works. Use FIXME to flag something that is bogus and broken. Use TODO to leave yourself reminders. Calling a program finished before all these points are checked off is lazy.
    -Partial Credit: Sun

    If I ask you to redescribe your problem, it's because when you describe issues in detail, you often get a *click* and you suddenly know the solutions.
    Ches Koblents

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