thanks guys. didnt know how acurate that rpm per volt equation is as i wouldnt of thought it would be an equal rise between the voltages. increased heat and all that gubbins may play a role in slowing the increase to speed down as the rpm goes up? guess not lol

geoff i plan to add another 2:1 on it. hopefully it wont burnt out.

On another point do you know how good the astro 25s are at takeing load? hopeing to use one in the selfrighting arms.