directions of sensors correspond to the vertical, the
for-and-aft and the left-to-right direction respectively
(Figure 2). The mini-tiller was combined with sensors,
data acquisition card and a laptop equipped with
LabVIEW SignalExpress; the sampling frequency was set
as 2 kHz; the slow forward speed was selected; the
vibration acceleration signals at the engine cover and the
handle were recorded under condition I, II, III and IV
(Figure 3). The speeds of the engine under each
condition were shown in Table 7.