Given the problems with the wheel bearings in NOTCam we had in semester 27, a complete overhaul of the bearings was made in November 2003.
New standard commercial bearings were purchased and were treated by a company in England. The company cleaned the bearings of their normal lubricant and coated then with a special coating. For all the worm drives these new bearings were installed. The method for doing the change of bearing has been documented on the web. Also for the camera wheel, one of the the spacers was replaced with a slightly thicker one which made the movement easier, though with no observed play of the wheel. It was found that although the focus mechanism had a none standard size bearing (it is thinner than the normal catalog units) a standard size bearing would fit. These have been purchased and also treated in England, but not installed.
From our own experience and tests done at the ING we expected these bearings to last well over a year. However, last week we again had a major problem with one of the filter wheels and it is suspected that this was again caused by the wheel bearings which were newly installed only half a year ago.
It still needs to be confirmed that the problem is Trula with the bearings, but if so we need to look for an alternative solution for the bearings. One such alternative are bearings which have been qualified for space operations. We actually looked at these type of bearing as an option for the overhaul but, apart from these bearings being very expensive, we could not obtain proper information from the Spanish distributer of the company. We now plan to pursue the option of buying these bearings further (e.g., buying them through an other country).