1st off what is the thickness of the Alum. that I used in the kits?
I am going to be making a few of the 3DOF legs from the kits here (8 total by the time I am done). But I a work on this project, I am not wanting a round tube for the foot leg and will have to custom build the pieces. I would like to have it matching as close as possible.
2nd where is a good resource that I can use to get some of the physics information answered? & what how to figure out the max weight the body can be (3-4 legs touching the ground at all times while 3-5 are not touching).
example if I add a 6" - 12" Rod shaft between the C brackets (Step 5)
How do I figure the weight Limits at the Other end of the servo to make sure I dont under power it or get the wrong servo for the job.
I’m not at home, so I can’t measure for you, but I believe that they’re about 1/16" thick.
I believe you’re trying to determine the proper length of the limbs, based upon how strong your servos are?
Well, here’s an example:
3 DOF leg = two “bones” (that would be the tubes that your mentioning) and 2 servos (we won’t count the servo attached to the body, since it won’t have to lift it’s own weight).
Now, the hip servos will need to lift the most weight.
The hardest way for it to lift is if the limbs are fully extended in a straight line.
So, let’s say you’re using a 120 oz.in. servo.
That hip servo can almost lift 10 ounces that are extended 12 inches from it.
Since the servos are about 2", that’s two 4" “bones” that you can have, provided that the two servos and two bones weight is under 10 ounces.
I need to get a 3 more of the 6" Alum Tubing (AT-04) and 2 more of the HUB-08 to finish the Skeliton part of the 2 legs (then get all of the parts again 3 more times )
1st step is to get 2 legs working and start working on the programing side of things, and building the rest of the computer housing (I am what you would call a computer case Modder and mixing robotics into it).
With those six inch tubes you’re going to have very little carrying ability. The longer you make them the harder the servos have to work to carry the load.
Well, if you go with the 3:1 (or greater) ratio, I doubt that you’d run into torque issues.
Keep in mind, though that your adding a lot of weight with three of them on each of the six limbs.
And, then there’s the slowing down of the servos.
But, that probably won’t be an issue, since no sane person would move a heavily loaded servo as fast as it could go, anyhow.
A note of warning, though.
I believe that the larger Hitec servos draw much more current than the normal-sized ones.
In fact, I believe that Dan Albert is having trouble with those same servos.
He made a biped out of large-scale Hitec servos and cut his own brackets to house them (you wouldn’t need to do that, since the “housing” is done by the reduction apparatus).
Anyhow, he’s having trouble supplying the amps that all those large servos demand.
Last time we met, he was using a huge set of Sub-D (I believe) RC car batteries, which he felt were way too much weight.
You might want to contact him ([email protected]) and compare notes.
By the way, you’ll have to worry about the larger gear in the reduction setup.
It might not fit the standard “C” brackets.
I’d say, go with the long “C” brackets, just to be on the safe side, and then all you’ll need to do is widen them to fit the larger servos.
Speaking of that, Mike created a website in which he outlined his conversion of large BlueBird servos, so that they’d fit the Lynxmotion brackets (mike-winters.com/)
You might find that useful.
its not that I can’t afford them … it just that I would have to spread it out a little more. I have only so much money budgeted per pay check to work on this.
Do I really need to High powered Servo on the R/L Joints?
Ok I got my hands on a few of the HiTec 805BB servos that I was thinking about using. And I know I was not putting 2 & 2 together once I saw them. They are considered a Mega Servo and Mega is the Size discription not streight They are nearly 4X the size of the standard servo. So I need to think about what path I want to go.
Keep using the 805BB and rebuild the Servo Erector set to fit the MEGA sized Servos (Items I would have to rebuild are the multi Purpose bracket & the “C” bracket).
start looking at the 5995 Servos and possibly lose 600 oz/in per servo.
I gotten 2 sheets of Aluminum for building the body but I am wondering if there is a lighter version of the Aluminum (have the 6061 Multi Purpose grade) Maybe the 2024 AirCraft Grade? At the cost of that I could almost start making Carbon Fiber pieces (I already own a 6-7lb Vacum for CF work).
I also played with them to make a larger arm (12" between axis). The PID on them isn’t ideal for robotics. The arm I built couldn’t even hold position. Not for lack of power, but due to overshoot. The thing was flailing around so much I feared for my safety. That’s just my experience. Remember, power is not the entire story here. Power with the wrong control method is no help. You need to be conservative, even with big “quarter scale” servos in the assembly.
They are nearly 4X the size of the standard servo. So I need to think about what path I want to go.
That’s just my experience. Remember, power is not the entire story here. Power with the wrong control method is no help. You need to be conservative, even with big “quarter scale” servos in the assembly.