Dave I have ordered these two items 380kg 24 volt servo.  https://m.aliexpress.us/item/3256803940067706.html?spm=a2g0n.detail.1000014.7.6a91GSasGSasoe&gps-id=platformRecommendH5&scm=1007.18499.280016.0&scm_id=1007.18499.280016.0&scm-url=1007.18499.280016.0&pvid=bceb03cc-dc34-4663-bebc-6f95f5ff2b99&_t=gps-id:platformRecommendH5,scm-url:1007.18499.280016.0,pvid:bceb03cc-dc34-4663-bebc-6f95f5ff2b99,tpp_buckets:668%232846%238112%231997&pdp_npi=2%40dis%21USD%2146.84%2146.84%21%21%21%21%21%402101f6b516662383789808592ea533%2112000028121741621%21rec

and this super servo 300. It also come come in a 500  https://m.aliexpress.us/item/3256802208243932.html?spm=a2g0n.shopcart.0.0.14aa38daqt699h&gps-id=shoppingCartRecommend&scm=1007.13440.311564.0&scm_id=1007.13440.311564.0&scm-url=1007.13440.311564.0&pvid=3350a3a3-e204-4606-a0c5-199f447b5d09&_t=gps-id:shoppingCartRecommend,scm-url:1007.13440.311564.0,pvid:3350a3a3-e204-4606-a0c5-199f447b5d09,tpp_buckets:668%232846%238109%231935&pdp_npi=2%40dis%21USD%2168.0%2168.0%21%21%21%21%21%402101f6b716669678532437726ea7a5%2112000020502823804%21rec&_universallink=1&m_page_id=iymkddfinicaumiy1841f06d5e415c896fdf1da662

the following is a video lifting 23+ pounds at the end of a 38cm arm.  

These two servos will work for me for the J1, J2 and J3 joints the big issue is the elbow I need a linear actuator with position feed back and I have not found one yet that I think will work.

Thanks for the info and links. Wow, that little servo gearbox is a monster. I had considered using one like that a while ago in my robot. I can't remember why I decided not to. It looks like a wonderful solution. Have you figured out where and how to add feedback for position and speed control?

One more question; I see you're ordering the servos through AliExpress. I have often thought about buying through them. Have you had any experience before with them? If so how was your experience and shipping speed? It seems like everything they offer comes from China. They must be the Amazon of the Far East. LOL

The problem I've found with liner actuator's is that they are heavy and slow. There are high speed LA's out there but they are expensive and really heavy. When you find one please share it. I'd love to check it out.

Just another thought and I'm sure you have already thought about this; placing a heavy liner actuator in the arm will add a lot of weight that would have to be lifted. However with the monster motors you linked to that may not be an issue. Have fun!

Dave,  These servo's work like standard RC servo's but include many adjustments in terms of rotation up to 300 degrees. You can find more details if you follow the links to the product page.

As far as AliExpress I have ordered many things from them and had very good luck.  Sometimes you have to search to find the best price and shipping rates but overall I have save a lot of money ordering from them.  Yes it takes some time to get the products about a month normally but I have not found that to be a real problem for me as I have had many other things to do in my project trying different stuff.   Example: I needed to order 20 JX PDI-1109MG Digital Mini Servo's they were 118.00 from AliExpress and would have cost more than 200.00 from Amazon.   The 380kg servo with free shipping is 56.00 from AliExpress and 82.00 on Amazon.

I looked at the 6V servo based liner actuator's on servo City and one of those could maybe work for the elbow and also fit in the bicep.  If I can keep most of the weight around the centers of rotation I think I can make this work.

So for me to try this next design I am looking at about 270.00 in servos for 4 joints.  Then if you add all the hardware and filament purchased for the other failed attempts well lets just say these arms are getting costly to say the least.  But I am kind of like a dog with a bone when I want to make something work.

So when the Super servo gets here this coming week I hope my goal will be to make a J1 joint with it and connect the arm to it and see if it can deal with the weight.  If that works I will order a 380kg to make the J2 joint and test again and just keep moving down the arm until I get to the finger tips.

Thanks for all that useful information. Sounds like you have an excellent plan. I'm looking forward to your posts on this.

Hey Dave put this together tonight while I was watching TV again.  The first three joints using 24V high torque servos.   Just need to figure out the elbow joint.  I think I will have to use a liner actuator for that.  Need to research more on servo City and see if they have something that will work.

Hey, that's pretty impressive. Is that U bracket attached to the servo horn 3D printed or metal? If 3d printed and If you find you need more strength for that part and need to change to metal, perhaps you can print a cover to make the metal u bracket look more substantial. You know, just for looks.

I have decided for right now to just build the stock arms.  I just can't find a solution for the elbow joint there is just no room left in the bicep.  the forearm and hand including servos comes in at about 1.1kg I would need an liner actuator with a 50mm stroke that is strong enough to pull the arm up.  Servo City make some micro actuators I think may work but without knowing the math to figure it out for sure I am not going to spend the money.

I will at some point be starting a new post on another project I will be doing.  The Youbionic X1 build.  The goal with this one is to get it walking.