Hey, guys.
I had a bit of inspiration a few days ago about making a tiny 4-servo biped out of microservos.
The main reason is to kick-start my way into the world of dynamicly balancing gaits in an easier fashion.
I’ll be debouncing 8 momentary pushbuttons on the bottoms of this bugger’s feet and using their states to get him to make his own decisions.
I had started doing this with my 20-DOF biped, but it’s complexity was getting in the way of the learning process.
After talking with Jim, though, I found out how scary microservos are.
So, I’m going to take the easier way and stick with 422’s, which aren’t all that much larger or heavier.
Here’s what this bugger should resemble:
f10.putfile.com/thumb/8/23717122913.jpg
Since I wish to have a large stance to allow for a long stride (the hips turning makes it take a step), I knew that I couldn’t locate the weight at the “waist”.
This’ll also let him lean farther, since the feet will be a heavier counterbalance.
I’ve decided to make two boards, one being a “power board” that will have a 5V 3A regulator for logic, an adjustable 5A regulator that I’ll set at 6V, as well as some fuses and a bunch of other necessary passives/connectors.
The servos will draw off the regulated 6V, which will, hopefully mean more stable gaits.
I’ve noticed that a gait that works with a fully charged pack doesn’t always work with a more-drained pack, and vice versa.
That should fix it, and if it works, I’ll use it on the larger biped.
The other board will house a PIC18F2620 which will monitor the batteries, read the button sensors, and PWM the servos.
I’ve heard a lot about how some micros, such as the Atom can control servos “in the background” without tying up the micro.
I’ve been itching to try to do that, myself.
Methinks it can be done on a PIC by utilizing priority levels in the main loop as well as setting a timer interupt for 50Hz…
As for the LiPos:
Sparkfun has some nice LiPo’s rated for 2C.
Which means, the 2000mAh ones can get 4A drawn out of them at any given time without resulting in cell damage.
That should easily cover the 4 servos my project will be using, and would probably cover 8 without any worries.
I’ll be using two 2000mAh 3.6V cells as well as Sparkfun’s 2-cell charger.
A voltage divider and an ADC will monitor the LiPos and a transistor will cut the power when drained.
I’ll be using a 250V 3A fast-acting fuse to limit the current, as well.
3A is still way over what my 4 servos will draw and well under the 4A rating of the LiPos.
As always, my ideas are stacking up way faster than my $ are.
Right now, the priority levels are:
A few things for Midget and Mike’s sensor board.
A 30V hammerdrill-driven car for Midget.
Two OSMC-based 55V 300A speed controllers for the car.
A CMUcam2 (not the +), a bunch of laser-pointers, and some rangesensors all for the car.
And now this new bugger.
I really need to get meself a sponsor!
The good news is, though, doctors really like to poke me with needles.
Well, that’s not the good news, I suppose.
The good news is that they’ll soon be paying nicely for the opportunity to make a pincussion out of me.
A few pints of blood and a couple weeks from now, and I might just have enough $ to catch back up to where my ideas are residing.
