The spere comp gave me very good and long service with a Novak 4.5R motor. It did not last very long when I used a 3.5R motor with it. It seems like when I bought the unit the listed motor use was unlimited, but afterwards The Web site listed the 4.5 as the strongest motor it should be used with. I notice that now there will be a TC edition spere comp. I would certainly wait and get it if I wanted a Sphere comp. The GTB gave me pretty good service with a 3.5R in the Pan car. It eventually fried when a motor bearing seized. With 4 cells there should be less heat to deal with. Note that on both of these units the internal protection failed. (Notice also the reflexive tense, it fried as opposed to I fried it.
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So right now it is GTB or Mamba Max
John