ROBO1 robots?

How's about 17 servos, with 10 in the legs, for just over $1645.

http://www.sozbots.com/robo-one/buyone.html

And a 600 mAh battery, guaranteed to run it for maybe .... 10 minutes?

http://www.sozbots.com/robo-one/about.html

 

Only $1645? Heck, for that price, where is the buytwo.html page?

-- Gordon

So, I'm assuming, when one thinks of "budget robotics", this isn't
really the first thing that comes to mind :):). Actually, this is the
big problem with building any servo-powered walker. Most of the $$ goes
into buying the servos, even cheap ones.

[snip]
: So, I'm assuming, when one thinks of "budget robotics", this isn't
: really the first thing that comes to mind :):). Actually, this is the
: big problem with building any servo-powered walker. Most of the $$ goes
: into buying the servos, even cheap ones.

  I figured as much.  I've recently seen some video of a Japanese
competition and thought it was the coolest thing I'd seen in a while.  Time
to start dropping quarters into the piggy bank to pay for one of these
things - Then play with the programming, which sounds even cooler.

fun,
DLC
--
============================================================================
* Dennis Clark         dlc@frii.com                www.techtoystoday.com   *
* "Programming and Customizing the OOPic Microcontroller" Mcgraw-Hill 2003 *    
============================================================================

 Time

Servo used in Robo1 shown on the soz site = KRS-784 ICS Digital Servo
KON784 $89.99

http://www.e-clec-tech.com/kricsdise.html

17 servos*$89.99 = $1529.83. So, $1645 for the entire Robo1 bot
including 2 servo controllers sounds like a real bargain. [Gordon can
now buy 2].

8.7 kg/cm is only 120 oz-in, if I calc'ed right, so these aren't
especially large servos, but at Speed: 60° @ 0.17 sec, good speed for
the size.

You will also notice the lynxmotion walkers are up in the $500-700
range. Most of the $$ there is also in the servos. My octopod with
chintzy analog servos cost $200 for servos, and about $20 for
everything else [not inc controller].

[snip]

Dan,

Most of the servos I've seen have been in the $30-$40 range.  Is there
something special about these $90 servos?  If so, do you know what is it?

Thanks,
Robert

it?

Looking at a Tower Hobbies ad, all 6 Futaba digital servos shown are in
the $59-99 range.

it?

Hitec digital servos, $35-90 range.

http://www.balsapr.com/catalog/servos/hitecHDS.asp

Nice research. :)  Yes I was thinking of the low end Hitec servos which is
what I have with my Robix USBOR controller.

Thanks.

Some of it is marketing. The servo companies don't make money on the
low-end servos, so they offer units with enhanced features (coreless,
ball bearing, etc.) for those users who want performance. Folks are
understandably cautious about putting a $15 servo into a $1,000 model
helicopter, so they want something of better quality.

The very high end digital servos mught use coreless motors, precision
ball bearings, and resin or metal gears, all of which bump up the price.
And because there is less competition among these higher-end servos,
they don't have to trim every last dollar out of their margins.

Whether the digital servos in the Robo1 are worth the $90 I can't say,
but this price isn't unusual. There are some digital servos that cost
upwards of $120.

Though you'd be stressing them, I think it's possible to use much less
expensive servos, and run them at a higher frame rate, and still get a
lot of useful hours of experimenting. Maybe these motors won't last
quite as long, but you could replace each one 2-3 times over before you
spend the same money.

-- Gordon

Thanks for the info.  I never run my motors that long so I'll stick with the
low-end ones.

I've seen the Robo-one in action.  I like it a lot.  I wonder though what
they'll have to do to get rid of the movement "jitter".  Or do you need to
get into the $60k plus range like the Asimo to see that kind of fluidity?

Robert

fluidity?

Jitter and fluidity are slightly different things. To get really fluid
flow, you probably need to have a very good closed-loop control
algorithm keying off of several accelerometers.

Regards basic servo jitter, from what I gather, it does seem that the
digital servos are more prone to this than the analog kind. I know one
guy who was using a certain servo controller to control the digital
servos in his lynxmotion biped, but there was too much servo jitter. He
changed over to one of my servo controllers, which has very stable
1-usec resolution, and also a lot of extra filter caps on the servo
power buss, and it worked much better. He's now sending data to the
controller at 115.2 in order to get essentially closed-loop real-time
stabilization of the biped - although the controller wasn't really
meant for this :).

You will notice that very few off-the-shelf servo controller boards
have much in the way of filtering on the servo power busses, and you
probably need more filtering for digital servos, esp that they suck so
much current. Basically, "inductance" in the power and battery leads
can lead to noisy signals. Same problem, I think, as the "main
capacitor" in regular ESCs .... [you'll also notice that essentially
NONE of the model car ESCs we talked about on the other thread have
main caps - they're all too tiny, no room] ....

http://www.4qdtec.com/pwm-01.html#cap

Since Gordon mentioned that the power to internal servo motors is
interrupted for 18 msec and actually on only during the 1-2 msec
control pulse, I am beginning to better understand some of the problems
just mentioned. I can also see why it might be a mistake to have pulses
going to all servos simultaneously rather than in sequence, like the
r/c receivers use.


- dan michaels
www.oricomtech.com
=========================

The Robo1 uses digital servos for the torque, but in my (admittedly
limited) testing I found it possible to increase torque on a standard
servo by running it at a 200-300 pps frame rate. The servo got hot, but
with some intelligent control I think it might be possible to
dynamically change the frame rate for those times when torque demands
are lower.

Robo1 is storing speed and acceleration settings in the servo, which is
something digital servos can do, but you'd have to do this with a
dedicated microcontroller (the $5 kind). One MCU could handle several
servos.

You still need a ball bearing servo of decent quality...something along
the lines of $25 at discount (rather than $50-80 for digital). That's
$425 in servos. Figure maybe $100 for the controller, and $50 more for
other electronics. If you have access to a metal brake and basic
metal-working tools you'd be able to make the metal frame pieces.

In all you're still looking at about $600 to build your own from
scratch, not to mention a lot of work.

-- Gordon

I have a milling machine to cut frame parts.

If someone wants to come up with dimensions
for them, I'll cut them and see if we
can get a biped put together.

Rich

Well, several of us have CNC routers and mills and such, and guys like
Pololu, Lynxmotion, and Bruce Filener provide reasonably-priced laser
cutting by the minute. What we need are those dimensions! The design is
the trick.

-- Gordon

Check out

http://www.symbio.jst.go.jp/PINO/

not RoboOne, but similar and is a completely open design with all support
documents.

Scott

I have the time to cut them out for free
(cost of materials is only price)

#1)dimensions/ drawings
#2)cheap servos + servo controller
#3)cheap aluminum
#4)machinist (already have this)
#5)software

Rich

I'll tested std servos with update periods of 15 and 10 msec, and they
ran fine, and "seemed" to have a lot more torque, but I didn't try it
long enuf to notice heating. Alternately, I've used 40-50 msec update
periods, and the servos went really wimpy. I'm not 100% certain whether
the different effects are due to more/less torque per se, or just to
different responsiveness in the internal feedback loops.

With the longer update periods, you can turn the horns a long way
before the torgue builds up. I actually thought this might be a
software way of creating a "servo saver" - ie, a way to add in some
compliance to leg joints, eg, during footfall, etc .... might not work
too well for a biped, however ... tilt, tilting, over and down ....

Try 4 msec periods. That equates to 250 Hz. Some digital servos run at
300+ Hz.

If you don't mind the hack, you can always cut away some of the plastic
housing of the servo and stick a small heat sink onto the side of the
motor.


It has to do with the period of time power is applied to the motor. In
an RC servo the motor inside is powered only when the servo receives a
pulse. Between pulses it receives no power. This is why if you remove
pulses from a servo (we're talking analog here, not digital) they simply
stop.

Given a maximum 2 msec pulse every 20 msec means the motor is really
only receiving current 1/10th of the time. Going with a higher frame
rate may affect the PI loop in the servo, but different brands may
behave uniquely. I only tried it with some GWS servos, and there was
some overshoot (expected) in moving from one location to another. Given
a more intelligent controller, you could build acceleration ramps to
tackle most of this. This is what goes on inside a digital servo.

When the torque isn't needed by the motor you could revert to a 50 Hz
frame. That would conceivably prolong motor life, and for sure extend
battery life. Digital servos consume a lot of amps.

-- Gordon