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Q_bias^dcan be taken from any successful walk. In theory, we could use the Q^dvalue which gives a

stationary walk to reach any desired speed.

In practice, it may be necessary to choose a few

nominal bias values near the various desired speeds to achieve the broadest possible range of

control.

Other parameters require some trial-and-error.

k_pmust be chosen to relate a required

change in speed to a suitable change in Q^d
. If k_pis too large, the system will be too sensitive to

small errors in speed and fall easily.

If k_pis too small, the system may not respond quickly

enough to prevent a fall.

The size of the range of constant Q^dvalues which produce successful

(constant speed) walks for the given base PCG is typically a reasonable value for DQ_max.

Figure 5.1 shows the nominal RV range and hip plots of a series of trials using speed control with

balance parameters based on Figure 4.15.

The trials of Figure 5.1 use a composite choice of

RVs, consisting of a forward up vector RV component and a lateral swing-COM RV component.

This is done to avoid the tightrope walking and

uneven

step

length

associated

with

each,

respectively. The hold times for each time-based transition of the base PCG have been increased

from 0.2 to 0.25 to yield a natural stride rate of 1.0 steps/second.

Speed control parameters for

each control dimension are shown in Table 5.2.

A nominal desired speed of 0.4 meters per step

Q_bias^dis varied to generate various speeds around this operating point.

Table 5.2 - Speed control parameters

or 0.8 m/s is chosen.