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Topic: which servo would be suitable (Read 1 time) previous topic - next topic

Bluenosedwill

Hi I have never used a servo before but I am very interested in getting some and trying to eventually make a biped robot (long way off I am sure).
As my funds are limited i don't want to just buy the cheapest weakest ones around only to need more to buy more expensive more suitable ones later.
Im thinking a biped no more than a foot tall, made out of something light weight. Any questions or ideas very much appreciated.

cheers

cr0sh


Hi I have never used a servo before but I am very interested in getting some and trying to eventually make a biped robot (long way off I am sure).
As my funds are limited i don't want to just buy the cheapest weakest ones around only to need more to buy more expensive more suitable ones later.
Im thinking a biped no more than a foot tall, made out of something light weight. Any questions or ideas very much appreciated.

cheers


For a biped (or really any legged robot), you'll want your servos to be full ball bearing servos with all metal gearing. In other words, expect to spend around $50.00 USD or more per servo. This is because there is going to be a lot of weight and mass being moved; the servos need to be able to move (and stop!) such large masses, and the support of such mass (by the output shafts) need to be robust. Sleeve bearings (oilite - or on the real cheap servos - plastic) will wear out very quickly which is why you go for ball bearing servos.

Other ideas:

Your leg servos are going to need to be fairly robust; standard sized or larger. Arm servos, on the other hand - you might be able to get away with standard sized servos for the shoulder, and possibly smaller and cheaper servos for the elbow and/or hand/wrist - because not as much weight or such will be put on these parts (except when recovering from a fall, that is).

You might try to come up with a design that centralizes - or at least tries to move - the mass of the servos closer to the torso; using "tendons" to move the legs/arms. This will keep the mass of the arms and legs to a minimum amount, so that the servos closer to the body don't have to work as hard to move the mass; of course, the trade off will be that they will have to work harder to move the mass of torso and all the servos there, but there's also the advantage of that that mass stays in relatively one position - so you don't have to worry about the dynamics of balancing changes of the mass locations...

Also - springs - look into how you can use springs to recover energy and to help support the system...
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zoomkat

Quote
Im thinking a biped no more than a foot tall, made out of something light weight. Any questions or ideas very much appreciated.


If you want to start out big, then a kit might be in order. Otherwise build a simple bot first and work up from there. I think the below are three servo walking bots.

http://davidbuckley.net/DB/Inspire.htm
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Bluenosedwill

Wow great ideas thank you very much! got plenty to think about. and thanks for the link I will check them out now.

Many Thanks

oric_dan

#4
Feb 01, 2013, 02:11 am Last Edit: Feb 01, 2013, 04:54 am by oric_dan Reason: 1
DB has made a lot of cool robots. He's kind of The Original Mr. Roboto. For background
information, you can also take a look at the lynxmotion site. They have a number of
walkers shown, and the Brat style is relatively simple to build from scratch.

http://www.lynxmotion.com/c-1-products.aspx
http://www.lynxmotion.com/c-85-bipeds.aspx

Adding to what cr0sh said, the big thing with walkers is, you need strong servos, and
the more joints in a leg and the longer the legs are, the stronger they need to be. The
robot has to carry its frame and also its batteries. This is the most serious issue - some
people get carried away with making fancy frames out of aluminum/etc, and then the
servos can't lift it up. In addition, as the #of joints multiplies, the complexity of the gait
software goes up "much" faster.

cr0sh already has you thinking of things that can keep you occupied for the next 4 or
5 walkers down the road, ;-). The best thing is to start simple, and learn a lot, and use
that knowledge to springboard to the next walker.

JimboZA

Here's a UK supplier with servos from 6GBP. Might be worth buying once cheap model like that. If you buy an expensive "pro" one now it might still be the wrong one in the long run, when you get to detail design, and then you've wasted more money.

They operate the same from a programming / connection point of view, so whatever you learn with a cheap one running, say, sweep can be transferred.
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Bluenosedwill

again thanks for the the great replies much appreciated

michinyon

Look at what servos other biped type robots have used,  and use those.

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