Hi DJ / Jeremie   I found my way to the inMoov construction site and found this very useful.  I am going to order some Hitec HS805BB 'giant' servos ex US.  I will use these for my 'shoulder' lift in exactly the same way as the inMoov does.  I do see what you mean about these steppers and tho we know they will 'hold' while energised .. I have no fail safe for power down.  I also have the servos supplied in your EZ-robot kit which are higher torque and generally more robust construction than the 'standard' plastic geared Futabas I have been using.

Thanks for your help guys ...

Sweet - looks like jeremies solution is the best fit. No need to use the tic then

using servos with the inmoov shoulder design is great because it’s simply using regular servo function with no additional work needed

I will be using Tic + stepper for my carriage rack & pinion but I will use the Hitec HS805BB super servo in the shoulder .. all good now .. thanks Guys.

I'm very interested in your new B9 arm design using these new motors and servos. I've been down a two year prototype path a few years ago when I was designing my B9 arms. Your arms sound a lot like what I built with the various joints needing to be moved and controlled.

Did you 3D print your wrists and claws yourself or did you buy the set Bob R sells through the B9 Builders Club? When I designed and built my arms all I had available to me were the wrists and claws made by a vendor that is no longer active. These were very heavy and solid. It's been a while so I really don't remember the load I calculated that I was putting on the elbow joint at rest or while moving. Any servo I found simply could't lift the needed load or they would destroy their self's. Perhaps with the new lighter claws it's possible now to use these fairly inexpensive heavy duty servos and have them stand up to the punishment.

Something I learned in my search for the right motors and support materials in my B9 arm was that when figuring the load being placed on these parts you also need to figure in Joint Rotational Acceleration (top speed your motor will be moving the arm). There are several on line robot arm torque calculators and tutorials available that will help someone get an idea how strong motors and materials need to be. Here's just one from The Society Of Robots: https://www.societyofrobots.com/robot_arm_calculator.shtml . Please forgive if you already have this information.

As you probably know that among the new B9 Robot STL files now available there is one that lets builders print their own wrists and claws that are very light and very accurate to the original robot. Less weight is good. I have a set of Bob's light weight 3D printed claws that I'm looking forward to finishing and painting to replace my very heavy set I currently have on my B9 Arm.

I'm excited that there are now builders like you that are looking for a better way to build a fully articulated B9 arm that will fit in the torso and can move in and out. When I designed my retractable and fully articulated B9 arm nobody had been able to do it before. When I was discussing it with other builders I kept getting comments like: "it can never be done", "it's too experience to build", "there's not enough room inside the torso for all that", "the robot will fall over when the arms are out and moving around". All that just made me push forward and find a way. My biggest challenges were building all that so it worked, was as light as possible and have it fit through a 6' torso hole and inside of Will Hoff's rubber arm skin. Another challenge I had was getting a successful auto tune on the Kangaroo I was using with my Sabertooth for position and speed control.

I'm convinced there are better ways then my design that are simpler and cheaper to build and operate. There are many more people out there that are smarter in robotics then me and have better design ideas. There are also new and evolving equipment for this kind of stuff that I have no idea about or how to use. Good luck on your build and have fun!

Just for kicks here are just a few reasons I decided to use the DC Worm Gear Windshield motors and material I did:

Worm Gear Windshield Motors instead servos:  PROS: Quite (servos are so loud) Super strong Worm gear will hold position when powered off Durable. They last forever on cars. Made out of steel. Can be bought in different shapes, sizes, torque values and speeds Easy to control with motor controllers and micro controllers like Sabertooth/Kangaroo (once tuned) and EZ Robot/Synthiam Very easy to control if using a Sabertooth in RC mode Using the Sabertooth/Kangaroo I was able to get smooth, ramped and natural movements with the DC motor.

Cons:  Large Heavy Power hungry (mine pull just about 25 amps each top load) Because of size constraints of a B9 arm they are hard to mount a feedback device on like a pot or encoder Using ARC or ARC they are harder to send control signals to then servos.  Must have arms dead center before retracting into the body of the robot or extreme damage can occur. True with DC motors or servos. For some reason the Kangaroo has trouble with auto tuning this type of extended load. I ended up having to set a lot of the PID Coefficients manually.  Some slop develops in the worm gear making centering the arm up to dock and move back into the torso difficult.

I hope this helps and I'm looking forward to see where you go with all this! Have fun!!

PS: If you need to get more power out of a servo and abuse it more then it's designed considder a gear box for the servo to sit into. servo City has very nice sets that really preform. Many of their gearboxes have built in pots and can let the servo extend it's limits:  https://www.servocity.com/servos/servo-gearboxes

David .. ok well thanks for all of this.  I am using the claw and cuff designed by Ian Hughes ..which I then animated after the style of Robert Rossi's animated claw.  My standard Futaba (4.5kgcm) servo works fine for the claw.  I then looked at your current arm and decided to have a:

• wrist left/right joint
• elbow left/right joint
• elbow/shoulder up/down joint (bicep)
• carriage extend/retract

so the Futaba works with the wrist joint also.  I needed the EZ-robot servos (19kgcm) for elbow joint and I am going to try some nice CYS-S0650 (55kgcm) servos on order at present.  I guess I was just trying to see what I could do as an alternative to your 'bicep' DC motor .. the 25A current draw a bit daunting .. but it does look 'the business' doesn't it.  I will end up milling and machining my arm components as you have .. for now 3D prints will suffice.

So the worm gear slop was the cause of your centering issue .. yes .. makes sense.  You have saved me finding out short comings of Kangaroo the hard way .. thanks for that. Yes .. a couple of good heads up for me here .. appreciated.