Feb 6, 2007

Revisit: The Biped

Okay, now that I've got some more information on the HiTechnic Motor Multiplexor (Mux), it's got me thinking again about the (I hope) inevitable NXT biped. Robots such as the Robonova-1 from HITEC use anywhere from 12 to 20 motors to achieve a wide range of motions, including walking, cartwheeling, and dancing.

With the HiTechnic Motor Mux, a designer now has the ability to include a total of 19 (yes, 19!!) motors. Now, this would obviously require 4 Mux, each controlling 4 motors and then adding in the standard 3 motors for ports A, B, and C (on the Brick).

Let's do a quick survey of the Robonova-1 and see where all those motors go:

1 motor per ankle
1 motor per shin
1 motor per lower thigh
1 motor per upper thigh
1 motor for each hip
1 motor for each shoulder
1 motor for each arm/bicep
2 motors in chest

16 motors in all that give the Robonova-1 the ability to walk, dance, cartwheel, and more.

Now, the Robonova-1 uses an aluminum framework that has been machined to hold the servo motors in a humanoid form. The processor is hidden in the chest and the wiring is hidden in various places.

Could a LEGO Mindstorms NXT biped be built? I don't know. The creation would have to hold the brick and 4 battery holders to power the 4 Mux devices. The structure would have to be well-designed to ensure a strong body and to prevent the biped from falling apart from various stresses. The size of the NXT biped would also be much larger than the Robonova-1 mainly because of the size of the NXT servo motors.

I'm curious to hear from others on this - are there other weaknesses or limitations that would make creating an NXT biped difficult? Can you think of any reason why an NXT biped could NOT be created?

Jim

3 comments:

Jim German said...

I think a bot with all that functionality would be extremely difficult to build out of legos (I'm not gonna say impoosible, because nothing's impossible) The biggest problem is the power to weight ratio of the motors, and thier associated batteries. If you use a full 16 motors, its going to be extremely heavy. In order to create a skeleton that could manage that weight, the skeleton would have to be huge, which would inturn become extremely heavy as well, which would then require a stronger skeleton... and so on until the skeleton is to heavy for the motors to move. Unfortuantly while ABS is a great material to make Legos out of (fairly strong, very durable, easily molded) it is far from the ideal material to make a Huminoid bot out of.

If I had a big enough budget, I would instead try to build a biped using not motors, but pneumatics. The Pneumatic cylinders put out a huge amount of force for thier size and weight, as well as working in a similar fashion to the muscles that you are attempting to replicate.

Lee said...

I've been trying to create my own biped using two NXTs (look for nxtmech in nxtlog) and its pretty tough. The motors have a hard time with the stress of supporting the weight of 12 batteries and the supporting structure.

But, i think with proper gearing that its possible. For example, eric sophie's jama has more enough of the required motors to allow locomotion, but the programming is a nightmare since his robot uses RCX bricks. The NXT however, with its bluetooth capability can in theory sync up at least 12 motors or more with multiplexers! The robot would undoubtedly be huge, at least 4 feet tall in the scale of lego motors. But we're a big community, can't we suggest to lego to make smaller servos?

Sir said...

Having played with a number of the BiPed RoboNova type robots and many NXT bots. The answer is no, you wouldn't be able to build the same type of robot with the NXT. The motors aren't strong, fast or accurate enough.

That being said, a quadraped robot like the one Eric Sophie is building at the moment may benefit greatly from these new HiTechic multiplexers as well as their new sensors that are being developed.

Pity lego don't want to do much more with pneumatics.

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