Sabertooth problem - sending power to motors before arduino is ready

hi!

i got sabertooth 2x60 few months ago. , it's moment go full scale it.

the setup:
sabertooth
arduino
24v battery
2 motors
2 rc filters

arduino powered sabertooth 5v , boosted 9v, arduino gets 9v. needed because arduino sending pwm sabertooth, , power low send correct voltage pwm. it's ok.

the problem:
so, have motors , arduino powered sabertooth.
when close circuit, without usb connected, motors go full speed in reverse no matter code of arduino. when same usb connected, works fine.

so, works ok if arduino powered when sabertooth starts. tried start without usb , without motors connected , after few secconds (after sabertooth's fan stoped) connected motors , work fine.

the sabertooth feels 0v on pwm pins because arduino not ready , not sending anyting yet. if happens, if arduino becomes ready, pwm voltage not read sabertooth anymore. motors remain full speed in reverse.

this strange.
if disconnect motors , power it, receives right voltage.

my dip switches setup: http://www.dimensionengineering.com/datasheets/sabertoothdipwizard/nonlithium/analog/independent/linear.jpg

any idea how solve this?

i think there couple similar threads on similar topics.  try searching them, may problems.   i think, don't quote me, pin needed pullup or pulldown or something.  don't have beyond that. 

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