charliefedererer thanks for that post, its really answered a lot of questions about how to get a knee bend for me.
I always feel unstable when trying to bend my knees, thats why I can never quite do it. I think i tried to hold a bit whilst at the lowest position of the bend whilst the ball got back down to my hitting position from the toss.
Looking at the above I don't think I was loading up right either. My look like a banana but the opposite way to how it should be. I think this is because of no knee bend.
As a result of this I just abandoned trying to jump as I was just messing my serve up a lot of times.
As soon as i'm up to it i'll try and work towards what you guys suggest and post a new vid/sequence.
thanks so much