House rules for cavalry charges and combined arms, 
Eagles of the Empire 3rd edition:

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When a cavalry charge is executed, roll a die.  If the dieroll is less
or equal to half the morale of the target units, the cavalry only
rolls half the dice it normally would (round up).  (The units in the
target area are considered to have "formed square".)
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Justification: As many who have played Eylau agree, the cavalry
charges can be murderous, in fact they are probably too bloody.
(Historically the Russians appear to have taken fewer losses than the
French at Eylau; in the game it is inevitably the reverse and the
charges are a major culprit though not necessarily the only one.)  The
success of a cavalry charge also does not seem to have depended purely
on the individual combat results, but was largely determined by the
question whether the units formed square or not.  This overall effect
is represented by the rule, which quite appropriately makes good
troops more likely to resist the charge ("form square").

A successful square has no effects in other phases of
the turn since that would require recordkeeping and I'm not sure the
second order effects are worth that.

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I have repeatedly seen the game severely criticized because of the
Combined Arms modifier that gives a +1 DRM for any size attack even if
only one strength point each of cavalry and artillery are present.  I
agree this is a rather strong abstraction, but I prefer this rule to
there being no benefit from combined arms attacks at all.  However,
for those that can't accept the rule as written, before you junk the
game because of one dieroll modifier, I suggest trying the following:

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Apply the +1 Combined Arms modifier not to all dierolls in one
Assault, but to a number of dierolls that is at most four times the
number of strength points of the weakest combat arm involved in the
assault on that side (infantry, artillery, cavalry).  (You can select
any number other than four to adjust as desired.  In fact, I'd be
interested to know which degree other people consider reasonable -
please let me know.)

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