i need to make the top layer of a cake spin but i don't know what i need
Thats a hard one!! I make everything from scratch when i need to do that!
nobody makes anything (yet) I'm workin on it!!
You could mount a microwave turntable motor inside of some PVC pipe put through the middle of the lower tier(s). The top tier should have a plate that connects to the drive shaft of the motor.
You will need to know how many volts and amps that the motor uses. It will need an adapter to prevent over heating the wires and motor. The information is usually indicated on the motor or the packaging.
If you don't know anything about electronics go to an expert for help. Radio Shack might have some knowledgable techs that can set up something for you.
p.s. Welcome to CC!
you can get small battery operated turntables, that sit about 3" high, maybe shorter. they turn real slowly and are used for displaying jewelry or small objects. I got some from ebay.
0.661386787 pounds = 300 grams....that is how much the jewelry turntable will hold that I found new on eBay for $7.95 with free shipping and handling as of today, Monday...12/28/09
If the weight of the top cake is less than 5 lbs., you can use the Wilton spinning topper mount. http://www.wilton.com/store/site/product.cfm?id=3E30D296-475A-BAC0-5966D7C18F1CD126&fid=3E333677-475A-BAC0-50BF88054762C2B1 Sink it into the cake below. We did that for the WE Wedding Cake Wars challange.