Bipedal Robot - Urgent help needed about digital servos

[not_this_punk]

Hello everybody.

My graduation project is building a bipedal robot but I'm stuck.

CAN I make it using analog servos? Or do I really NEED digital servos and their capabilities like speed control? I imagine that controlling the servo speed would be recommended in a biped, but is it necessary? Digital servos are expensive and they require servo programmers that are very expensive (here in Romania at least).

I should mention that I will use C-programmed AVR microcontrollers.

Thank you in advance for any replies, they'll be very helpful and appreciated

[Fredrik Andersson]

You should not need to use digital servos. Although they would be a pretty good upgrade you should probably not get them if you don't have the cash for it. It will work fine with analog servos. Just get servos with enough torque and speed.

PS. you can speed-control a analog servo as well, but that is done software-wisely

Good luck with your project!

[not_this_punk]

Thank you for your quick reply.
Yes, I know I can control the speed of an analog servo but that involves dividing the move into smaller steps and considering the way an analog servo works (full torque is applied after a relatively long period of time), this seems that will diminish the torque rather drastically.

Anyway it's good to know that analog servos will do. But yet I have another question. I'll most likely use multi-purpuse brackets and C brackets from Lynxmotion as an exoskeleton and 5 servos/leg, like here: http://www.lynxmotion.com/images/jpg/ironmanl.jpg except that I don't think mine will have hands, so there will be 10 servos in total.

Considering that mass+a 5 battery pack, and maybe the mass of the torso as well, what do you think would be the minimum torque for the servos? I know that higher is better, but I don't really want to spend that much on analogs. Also, just to be sure, would it be A LOT easier using digital servos, considering the fact that I'll have 5 DOF per leg?

[Admin]

In terms of control, both digital and analog servos are exactly the same. Neither have built in speed control, and neither are guaranteed to travel at the desired speed or desired location you tell them to go to.

A major disadvantage to digital servos is that they require much higher startup currents, for the benefit of increased torque and reaction speed. If you have 15 servos requiring much more current, that means your batteries will be straining to supply the energy your robot requires. And then there is the cost.

That being said, just stick with analog.

[rogerfgay]

Almir Heralic recommends BMS-380 Max servos, as you can see from the video of the bipedal robot that he created as a student project - HR-2. I believe Almir got his directly from the company, at a very low price, after explaining he was doing it as a student project. I've also seen some on eBay for a couple of bucks.