the key is powerful motors. you're not going to have a very good rambot if it moves at 5mph. storm 2 uses lem 130s i believe and runs at 25mph so if i were you i'd aim for 20+ mph and use eteks. lem 130s are hard to find now and cost over £1000 pounds each where as eteks are much cheaper. the new etek r (replacement of the original etek) costs $470 from robot market place. i have also found a very high power motor that looks suspiciously like an old style etek popping up on ebay alot:

http://cgi.ebay.co.uk/8000watt-DC-gener ... _782wt_907