ROBO1 robots?

Reply to
Mark
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Dan,

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

Thanks.

Reply to
Robert Oschler

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

Reply to
aiiadict

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

Reply to
Gordon McComb

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

Reply to
Robert Oschler

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] ....

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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

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Reply to
dan

I've seen people rip out the innards of standard servos replacing it with custom control (say a H-bridge and a little AVR). Much more important that the obvious much better control over torque and speed is the fact the it enables feedback about current position, current torque, etc. Not very useful for RC, but very very useful for walkers.

$0.02, Tommy

Reply to
Tommy Thorn

I've got a website detailing progress on a bot I've been building. It's at:

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You basically have to use high torque servos. I used low-cost HS311 servos and they didn't have enough torque to allow the robot to walk.

The HS5645MG are the recommended servos because they're powerful enough and they generally cost ~$60 each.

I've got 12 DOFs in the legs (six each side). I've got a board set that I've been experimenting with and everything is onboard. For control, I've got an ATMEGA32 to generate motor sequences.

Ed L

Reply to
Ed LeBouthillier

Nice idea, I had not even thought of that aspect of it!

Bob

Reply to
MetalHead

dan wrote: Dan,

[snip] : Now, this is really interesting. I've never dug into the servos, but : given this info, I can see why they get wimpy with 40-50 msec update. I : can easily set my servo controller to shorter update periods, so I'll : play around some more and see what happens. I suspect this could be : useful with a servo-powered mini-sumo when you need some xtra oomph : during the tussle [don't tell Dennis, his sumos win too often already].

Been there, done that. I now yank the guts and drive the motors directly, even more power there. ;-)

: - dan : ============

DLC

Reply to
Dennis Clark

update. I

already].

motors

see the other thread.

Reply to
dan

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