It appears we have the same problem, I've been going nuts for about 4 months, first trying to buy one and secondly trying to make one. Both were useless. The only Graupner dealer in the US couldn't/wouldn't help and making one had some pitfalls. I'm going to try building one again, but I got frustrated and gave up a few weeks ago. If your in Sweden maybe you can find a Graupner dealer that will help you, or maybe you can call them directly. The guy at the US dealer said that Graupner of Germany wont deal with customers personally, yet they wouldn't help me. Perhaps you will have better luck and if you do let me know. So far the only answer I've gotten was, buy a new drive, lol, a whole drive for an impeller. [:@]

Here a link to my thread about this subject.
http://www.rcuniverse.com/forum/m_5133305/tm.htm

~QS