@rgordon and others i designed h-bridge design and pcb boards all info in zip file,made this design awhile back and sold many boards if anyone needs to buy the boards let me know,more that buy the boards the lower the cost to have it made ,boards are in 2 parts ,main reason is that the board is universal logic circuit on one board and pwm h-bridge on another rated at 60 amp cont,but you can easy remove mosfets to save money,remove 4 of the 8 mosfets give you 30 amps i dont get money from this and dont need it HBRIDGE.zip files in bmp and sch and parts list

Rgordon, To answer your question about bending the waist. I am going to have to take some pictures this weekend and start my own thread in Project Showcase. I made it pretty cheaply, and if you look at the pictures it is easy to figure out, but you will see that it is very hard to describe without looking at it. confused

rgordon Danger! is correct yes bending the waist is very easy done it on a few robots ,not hard or high cost ,with already made parts or easy to make parts,mostly depend on the weight you need to bend and that would the torque needed to bend and return, bending is very easy but returning needs alot more torque

on the h-boards i am selling adding a special stall and what i call under stall (i guess it can have a better name) stall is easy its when your robot bumps into something or a gear gets jammed and you could burn out the motor or h-bridge

now on under stall.it when your robot goes on to a carpet or some thing and motor keeps spinning and does move there is a way to detect that both conditions you can have to shut down the motor or go in reverse or turn off the robot as you can see i love designing circuits 20 hours a day ,and sometimes think about when i am sleeping and passing it free to others

rgordon If you are still interested in how I am making my robot bend at the waist, I have pictures
here. It is all cheap hardware.

my RAD 4.0 will have bending at the waist ,using legs like on a person and using strong servo's ,has more then a 40 lb lift

if you have a bigger robot,look at windshield motors very high torque and i use a h bridge connected to a FUTABA S3003 BOARD ,i use this for my main robot arms to each lift near 50 lbs may be more,very high servo's

@ Rgordon: know these high-torque servos and low price (30kg: 72 pounds), I filisofia to find a powerful yet inexpensive servo I found these, now I have one mounted on the head of my robot RSP (soon I'll upload the photos) his strength is great! watch your fingers, you can attach a machacarlos.y if the servo pinion gear ring with a large and well make a speed reducer would gain much strength. If you have occasion to balance the center of gravity of the robot arm with the axis of the servo (it may be impossible at times), but at least put some weight that is more useful patra balanced, this helps to reduce torque servo, here are some ideas that I implemented in my project, I hope some will be useful.

Big servo

Thanks! Wow, that's a good price. Strong too! 28.6 lb.-in. I may have to have some of these.

i buy alot from hobbyking,does take a very long time to get to usa stress