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JR servos

ArchiverArchiver Posts: 46,084
edited 2000-07-18 14:30 in General Discussion
Does any one have experience with these? I am thinking of purchasing some
JR517s (ball bearing) to make a 12 servo hexapod. Are these suitable? I
can get a good deal on them, they cost $45 new, and I can get them for $30
new. These are Canadian prices. The typical american price is $27. I
believe that they are high quality, but am not quite sure. I'm not looking
for comparison on specs. I have found those already. As with any other
products, some manufactures will over rate their stuff and other will under
rate it, but I won't get into that now. I want to know if they are
reliable, durable, smooth (being ball bearing I assume they are), and long
lasting. CAn anyone offer some advice?
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Comments

  • ArchiverArchiver Posts: 46,084
    edited 2000-07-17 13:14
    --- In basicstamps@egroups.com, "ED Ward" <punk__rocker@h...> wrote:
    > Does any one have experience with these? I am thinking of
    purchasing some
    > JR517s (ball bearing) to make a 12 servo hexapod. Are these
    suitable? I
    > can get a good deal on them, they cost $45 new, and I can get them
    for $30
    > new. These are Canadian prices. The typical american price is
    $27. I
    > believe that they are high quality, but am not quite sure. I'm not
    looking
    > for comparison on specs. I have found those already. As with any
    other
    > products, some manufactures will over rate their stuff and other
    will under
    > rate it, but I won't get into that now. I want to know if they are
    > reliable, durable, smooth (being ball bearing I assume they are),
    and long
    > lasting. CAn anyone offer some advice?
    >
    I've used JR ball-bearing servos (517 and others) for their intended
    application (flying airplanes), along with other JR products, for
    quite some time. I've always found them to be well-made, smooth, and
    reliable. I've never used them in a robotics app, however.

    Chuck Davis
  • ArchiverArchiver Posts: 46,084
    edited 2000-07-17 13:47
    Hello Ed,

    I've used tons of RC servos over the years (for everything you can imagine
    - including your application). A few points to consider:

    1. No (major manufacturer) servo will last more than ~100 hours of
    continuous running. Even with good mechanical design, this is an
    unfortunate rule of thumb.

    2. Servos will always fail. This can be assured by over loading them. In
    your application this means weight is the enemy.

    3. I've had good luck with JR servos. They seem to be more on par with
    Futaba stuff and superior to Hitec and clones. Last year I did a project
    that required several of their new high torque NES4721 digital servos, and
    these worked well. We still had to replace them now and then, even at 130
    oz/in! I think what you're considering is a good choice...

    4. In an application that requires many servos (yours) I always obey a
    basic rule. If I'm paying for them, I get a good quality basic model (ie.
    Fut 148, 3003, etc.) and replace as required. If someone else is paying, I
    buy the absolute very best (read: most expensive) and save myself *some* of
    the maintenance headaches.

    5. The hexapod I'm referring to had 12 standard futaba servos and they
    failed with a certain regularity in fairly heavy use (TV series). These
    things were, however being strained to their absolute limits - they could
    only *just* lift it for walking. Again, if you can make your 'bot lighter
    they will last longer. Maybe build the chassis out of plastic instead of
    aluminum?

    Hope this helps, Duncan
  • ArchiverArchiver Posts: 46,084
    edited 2000-07-17 15:20
    JR has been in the RC business since I can remember. Their stuff is durable
    worst case, and IMHO one of the best choices out there (HiTec/RCD's FET
    servos are up there too).

    -dave

    Dave Paton Motorola Advanced Technology Center
    voice 847.538.7575 pager 888.773.6802
    A13593@e...

    >
    Original Message
    > From: ED Ward [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=H77MI4XiTKVONKynqV1fxmn8oCF73XT0MvFNrUzRAeV-8AYD911i8HR30qqef6C7gp3tVXy7rp9_J9hjZOQj8AcBhA]punk__rocker@h...[/url
    > Sent: Sunday, July 16, 2000 11:41 PM
    > To: basicstamps@egroups.com
    > Subject: [noparse][[/noparse]basicstamps] JR servos
    >
    >
    > Does any one have experience with these? I am thinking of
    > purchasing some
    > JR517s (ball bearing) to make a 12 servo hexapod. Are these
    > suitable? I
    > can get a good deal on them, they cost $45 new, and I can
    > get them for $30
    > new. These are Canadian prices. The typical american price
    > is $27. I
    > believe that they are high quality, but am not quite sure.
    > I'm not looking
    > for comparison on specs. I have found those already. As
    > with any other
    > products, some manufactures will over rate their stuff and
    > other will under
    > rate it, but I won't get into that now. I want to know if they are
    > reliable, durable, smooth (being ball bearing I assume they
    > are), and long
    > lasting. CAn anyone offer some advice?
    > ______________________________________________________________
    > __________
    > Get Your Private, Free E-mail from MSN Hotmail at
    http://www.hotmail.com
  • ArchiverArchiver Posts: 46,084
    edited 2000-07-17 23:42
    Thanks for the input. I am thinking of building my bot out of alumunum, the
    way I figure, a little aluminum is lighter than a lot of plastic. I plan to
    have the whole body based around on 1-1/4 inch piece of aluminum (so I can
    fit some sub-Cs inside). On some of the flat pieces I might drill a bunch
    of whole to further reduce the weight. Also I plan to use some springs or
    elastics to offset the force the servo's need to exert to lift the bot.
    Might it be a good idea if I "rotate" the servos? Obviously, the "lift"
    servos will be the first to go, so swapping them with the "swing" servos
    every 20 hours or so, could help equalize the wear.


    >From: orthner@s...
    >Reply-To: basicstamps@egroups.com
    >To: basicstamps@egroups.com
    >Subject: Re: [noparse][[/noparse]basicstamps] JR servos
    >Date: Mon, 17 Jul 2000 08:47:55 -0400
    >
    >
    >Hello Ed,
    >
    > I've used tons of RC servos over the years (for everything you can
    >imagine
    >- including your application). A few points to consider:
    >
    >1. No (major manufacturer) servo will last more than ~100 hours of
    >continuous running. Even with good mechanical design, this is an
    >unfortunate rule of thumb.
    >
    >2. Servos will always fail. This can be assured by over loading them. In
    >your application this means weight is the enemy.
    >
    >3. I've had good luck with JR servos. They seem to be more on par with
    >Futaba stuff and superior to Hitec and clones. Last year I did a project
    >that required several of their new high torque NES4721 digital servos, and
    >these worked well. We still had to replace them now and then, even at 130
    >oz/in! I think what you're considering is a good choice...
    >
    >4. In an application that requires many servos (yours) I always obey a
    >basic rule. If I'm paying for them, I get a good quality basic model (ie.
    >Fut 148, 3003, etc.) and replace as required. If someone else is paying, I
    >buy the absolute very best (read: most expensive) and save myself *some* of
    >the maintenance headaches.
    >
    >5. The hexapod I'm referring to had 12 standard futaba servos and they
    >failed with a certain regularity in fairly heavy use (TV series). These
    >things were, however being strained to their absolute limits - they could
    >only *just* lift it for walking. Again, if you can make your 'bot lighter
    >they will last longer. Maybe build the chassis out of plastic instead of
    >aluminum?
    >
    >Hope this helps, Duncan
    >
    >
    >
    >

    ________________________________________________________________________
    Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com
  • ArchiverArchiver Posts: 46,084
    edited 2000-07-18 14:30
    Ed,

    At 03:42 PM 7/17/00 -0700, you wrote:

    >Thanks for the input. I am thinking of building my bot out of alumunum, the
    >way I figure, a little aluminum is lighter than a lot of plastic.

    This is true, but you do have a minimum structure that's required - the
    thing has to have six legs...and most of the weight is in the 12 servos, no
    matter how light you make the chassis.

    >I plan to
    >have the whole body based around on 1-1/4 inch piece of aluminum (so I can
    >fit some sub-Cs inside). On some of the flat pieces I might drill a bunch
    >of whole to further reduce the weight.

    Yes, relieve it as much as you can, and start with as thin a piece as you
    dare...

    >Also I plan to use some springs or
    >elastics to offset the force the servo's need to exert to lift the bot.

    Be careful. If the servos are at or near their torque limit (40 oz/in) when
    lifting, any assist will have to be overcome during 'steps' - further
    torqueing the servo. A good design is to position the servos *on* the leg,
    outboard of your hinge mechanism. This way, during the lift part of the
    gait (I'm assuming a tripod gait) at least the weight of six servos doesn't
    have to be lifted - they're on the 'planted' legs. With this scheme, during
    each step you're only lifting *half* the servos.

    >Might it be a good idea if I "rotate" the servos? Obviously, the "lift"
    >servos will be the first to go, so swapping them with the "swing" servos
    >every 20 hours or so, could help equalize the wear.

    This is a good plan. I also thought of buying higher torque servos for the
    'lift' position and using standard ones for the 'swing'...

    Good Luck, Duncan
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