| They may also be configured without mixing to be two independent speed
controls. This lets you control your vehicle with two joysticks, one for each motor, and
perform the turning algorithm with your thumbs. The RDFR is the only controller that gives
you your choice of steering methods. Yet another configuration provides a dual output
controller with a single switchable command. RDFR DIRECTORs are compatible with most
model R/C systems including PCM or FM and plug into your receiver like a servo. They're
available with Futaba J or G, Airtronics, Deans, or JR connectors; please specify when
ordering. The RDFR family replaces our older DFRM type.
Inside an RDFR are two rugged forward/reverse speed controls coupled together through
special logic that generates the differential right and left motor rotation needed to
guide the vehicle. The logic also validates the R/C signals. If they are out of tolerance
the last known good command is used. However, a majority of faulty signals safely shuts
the motors off. The RDFR DIRECTOR is designed without relays for professional applications
requiring repetitive forward to reverse commands.
The optically isolated outputs are Pulse Width Modulated full H-bridge circuits
originally designed for Permanent Magnet DC wheel chair motors. N-channel power MOSFETs
are paralleled in each H-bridge leg to achieve the specified amperage. For example: the
RDFR38 contains 48 70 Amp MOSFETs. In contrast to hobby controllers VANTEC's MOSFETs are
all properly thermally mounted flat to the metal heat dissapating case with special
insulating washers.
The driver PWModulates the bottom half of the bridge while holding the diagonal upper
bridge leg on in order to effect efficient re-circulating currents in the motor.
Sequenced electro-dynamic braking shunts the motor by modulating both top legs of the
bridge. With a command to "stop" the brake is gently ramped from 0 to 100% duty
cycle. When an R/C command that changes direction is received the brake is quickly
sequenced to first bring the motor to a halt, then the reversing PWM power is ramped up to
the commanded speed. This forced sequencing minimizes motor "plugging" and
stress on mechanical components. The implementation and timing of these functions is user
selectable.
Output current through the MOSFETransistors may compression limited above a threshhold
by PWM duty cycle limiting in RDFR21-23 models. There's a threshhold adjustment trimpot
for each output. Some short circuit protection is provided. |
