Cyloh, dont underestimate the difficulty of one arm negative let alone the positive one arm chin up. If you dont gather the proper body strength, you will have higher chance boarding the train of injury. I assume that you want to pursue this too?

I saw your post and I just had to do one arm negative again for comparison. I do 2 close hand chin up to the top, tense the body, and release the hand and ask my sister to start click the clock time counter the moment I begun to descend. I can control descend from top to bottom as of now with my strongest right hand in 12 second. I've read it somewhere that 20 second is the mark to aim at in general... I was surprised myself.

Body twist is normal for one arm hanging. I dont know how because I cant do one arm chin/pull up yet as to fully understand the twisting effect. However, I've read again and again that the twisting is normal. Some people just go with it, some people try to put their hand in front and try to push it and the body the other way around (you will read a lot of comment mentioning "turn in", "cockscrew" etc2). I dont remember how I descend, but I think I twisted also, but it is not that bad because my body is fully tension, and I'm too focused on maintaining body tension especially at my bicep, grip, and maintaining proper tension on the area between pec and shoulder joint.

If I'm lucky to get the one arm chinup, I will try to describe this again.

I still think that I need to work on weighted chin up a little bit more. Actually I'm planning to do more weighted pull up because I'm having trouble to get proper form (chin over bar) even with 20kg. No need to rush... anyway, I'm happy with my level right now...

Take the long view.

BTW, nice idea you have there on two pull up bar. I think yours is like a version of towel assisted one arm chin up... If I'm going to compare this to towel chin up, the fewer the fist length of your assisting hand, the easier it gets. You can put the bottom bar higher.