flipped mode or serial override. One solution to this problem is to use the “ignored channels” configuration
parameter to set unused analog channels as ignored. The TReX considers ignored channels to be fixed at
their neutral positions. An alternate, purely hardware-based solution would be to short any unused motor
channels to a used one and to tie any unused “enable” channels (4 or 5) to Vcc (the 5-volt line). By shorting
unused motor channels to a used one, you should be able to get past the safe-start portion of the TReX’s
start-up routine.
4.e. Safe-Start Mode
When the TReX starts up in either RC or analog mode, it first enters safe-start mode. In this mode, the three motors
are shut down and are unaffected by the channel inputs. The TReX lets you know its in this mode by rapidly
flashing its green status LED. To exit this mode, the following conditions must all be simultaneously met:
1. All required channels must have a valid signal. This only applies when the TReX is in RC mode since it’s
not possible to have an invalid analog signal. Required channels are determined by the “required channels”
configuration parameter. Only channel one is required by default.
2. All motor channels must be close to their neutral values (i.e. they must not be instructing the motors to move
very quickly). Channel 5 must be disabling serial override. The TReX will not allow you to start with serial
controlling the motors if you’re in RC or analog mode.
If you have floating channels while running in analog mode, it may be impossible for you to satisfy the safe-start
conditions. Bullet point #2 in the analog section (
Section 4.d
) provides several ways to fix this problem.
Once you have satisfied the safe-start conditions, the green status LED should stop flashing and turn solidly on. This
indicates that the channel inputs are now in control of the motors.
Pololu TReX User's Guide
© 2001–2009 Pololu Corporation
4. RC/Analog in Detail
Page 14 of 22
