Questions about my Quadruped

[Baltar]

Hello all,

I recently started building a quadruped robot using the Lynxmotion quadruped body kit and 3DOF SES legs.



For the horizontal joint and 3rd (end) joint, I am using Hitec HS-422 servos, and for the middle (vertical) joint, I am using Hitec HS-635HB servos. I am still waiting for more parts, but I plan to mount onto the chassis an Arduino Mega 2560, an SSC-32 servo controller, one 2800mAh NiMh battery for the servos, and one LiPo 2200mAh battery for the logic boards.

I currently have the robot built with everything except the servo controller and the LiPo battery in place, as I am still waiting for them to arrive. The question that I have is how do I know whether or not the robot will be able to stand once everything is in place? Unpowered, the robot is unable to stand, although it will balance as shown in the image. The battery that I have mounted within the centre of the chassis is quite heavy, which is why I am concerned, and I am yet to add the other battery (and I don't know where to mount it - but that is another problem).

Is it reasonable to expect that these servos will carry a robot with a pair of fairly large batteries and a couple of controller boards?

Thanks

[eriklely]

I was looking at you design. And actually a have one pretty similar, only hexapod for now. In the past i had a hexapod version exactly the same parts as you are using, only two legs longer . Thing is, with the two batteries and all, even the hs475 weren't that strong. It cost me some gear for sure. I ow 422 ones as wel, but mostly use them for pan & tilt in a cam. They not really fast en more important not particularly strong. I would at least suggest that you do some testing without the batteries.

By the way, why would you need two batteries that size. A big one for servo an a much smaller one for logic should be enough i think. I mostly try to use 1 battery for the both, for weight reasons. And if you are using 1 for the servos and one for your arduino, i guess the servo bat is empty after 15 min max, so that's the max the other battery has to run as well i guess.

The fact that it can't stand without the servos being powered really doesn't say a thing. Well mostly you can in fact put it in someway in balance such that it stands. But i wouldn't really worry about that.

Hope it helps.

[Baltar]

In this case, I may remove the battery that I put in place, and I may use a smaller one (say, 1600mAh) for the servos. Then I may also use a much smaller battery for the arduino, too (something like a 9V rechargable cell?).

Thanks.

[Matt Denton]

If the tibia servos (third joint) stay roughly where they are with respect to ground they require very little power, as most of the weight is carried by the servo bearing. However the femur servos (second joint) will require the most power, here I would suggest the HS-645MG servo if you have trouble with the servos you have. But as Erik points out, start with the batteries off-board and run power in via a cable to reduce weight.