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Posted by Gordon McComb on October 13, 2005, 1:16 pm
Speed-wise I think you need to go no less than 1 rps. These motors are a
bit too slow; the exporter ought to be able to supply some other gear
ratios. I know there is a market for small motors for micro and nano
robots, but I think it's a less significant market than desktop robots
that use standard servos. If anything, people tend to ask for servos
that are beefier and faster that the typical Futaba S-148 (or knockoff).
That makes the target >1 rps, and >56 oz-in (at 6vdc).
If you can manage the motor and optical encoder for $20-25 that would
place it at a competitive level with a $10 servo and a $10-15 (per side)
encoder setup, but not a jaw-dropping price. Remember that an R/C servo
doesn't need an H-bridge, so while control is not as precise as regular
PWM, there's less to design, and overall less cost. RC servos are
popular not so much because of their features, but because of their low
cost, plus ease of use.
Linear servos: I've seen retrofits for taking a standard servo and
making it linear, but unless you need the more precise movement, most
people just use a bell crank, and live with the (somewhat) non-linear
positioning.
-- Gordon
Thomas Arundel wrote:
>
> We're thinking of designing and manufacturing some servos aimed at the
> robotics hobby market, with 360 degree rotation and feedback provided via an
> optical encoder - target prices about $20-25 each using miniature precision
> motor / gearbox combos similar to these:
>
>
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item `05416519&rd=1&sspagename=STRK%3AMESE%3AIT&rd=1
>
> That we're now starting to import from Asia. As well as traditional PWM
> encoding, we could also consider encoding schemes like i2c. We're planning
> on designing some even smaller models based around mobile phone / pager
> vibrator motors.
>
> It would seem that many people use RC servos, though there seem to be some
> compromises, and I think we can improve on weight and torque as well as
> offering arbitrary positioning.
>
> I'd appreciate some thoughts, about the shortcomings of RC servos, and on
> which areas we should focus to design a servo that's better for building
> robots...
>
> Also, does anyone know of any linear servos? Do you think those would be a
> popular product, and if so in what sort of size / configuration?
>
> Cheers,
>
> Tom.
>
> --
> Thomas Arundel
> TL: +44 (0) 1932 252482
> FX: +44 (0) 870 137 6005
> EM: tom@fastcomponents.co.uk
> -----------------------------------------
> Fast Components Limited
> www.fastcomponents.co.uk
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> some robust stuff for "real world" bots please! :-)