Hi Daz, I sent you an e-mail yesterday, did you get it?
Right,down to business, your servo cam is normally produced from a large servo disc and it has three functions:
1: open the valve and switch on the pump to fill the tank.
2: Stop the pump and close the valve , trapping the ballast water in the tank.
3: open the valve (pump still off) and allow tank to empty.
The shape of the cam is given in a (not to scale) drawing provided in the instruction manual and it is a guide to the working profile. You don't have to make it exactly as shown but it must function in the manner I have described above. The cam in my own boat is not exactly to shape but it does prform the correct function. Read the cam profile sheet so you fully understand what is required and it will all become clear. Get hold of a couple of large servo discs and have a go at it and if you get one wrong, sling it in the bin and make another because once you get it right, you won' need to look at it again.
Re your High Tech servo, I am not familiar with Hi Tech gear as I have always used Futaba but I know people have used it and it seems ok just so long as the servo is a standard size and fits the hole in the servo tray it should be ok. I do know that if you replace that servo with a Futaba unit at any time, you will find the Hi Tech servo disc will not fit the output shaft.
Regards. ..Chris