Tamiya 56505 - 1/14 R/C No.5 Motorized Support Legs For Tractor Trailer  [56505]

That is a good Hop-Up to add Realism towards Tamiya King Hauler kit.

Everything required (minus servo) to help you to drop the feet and unhook your trailer by a 4 channel radio. Retractable leg engines operate on 4 AA batteries(perhaps not included) you mount under trailer.

Specs and Features:

• Two AA battery pack cases
• One RS-29 motor
• Two battery pack instance connectors (they're regularly link the 2 battery
  instances)
• One battery terminal A
• One battery pack terminal B
• One tube of silicone oil (1/4 oz., for the gears)
• One coupler plate A
• One servo plate
• One switch plate
• One worm gear (acts similar to a pinion)
• One 28 teeth / 12 teeth counter gear
• One 36 teeth / 10 teeth counter gear
• One 40 enamel gear
• Two return springs
• One inner springtime
• Four rack springs
• One 2x67 mm threaded shaft
• One 2x50 mm threaded shaft
• One 3/4" x 4 3/4" double sided tape
• One 20x20 mm dual sided tape
• One change gate (used in the transmitter as helpful tips)
• Three nylon adjusters (a.k.a. 4mm ball cups)
• One 5x40 mm plastic tubing
• One 4-way wrench
• Two steel racks
• Two joint cups
• Two metal rack pinion
• Two pinion shaft
• Two 5mm washers
• Two 5x8 mm bronze bushings
• Two 3x7 mm bronze bushings
• One drive shaft
• One brass hex hub
• One hex wrench
• One brass rod nut
• One on/off switch
• Two coupler peanuts
• Two 4 mm ball connectors
• Two 4 mm e-ring
• Four springtime pins
• Four 3x3mm grub screw (a.k.a. hex screw)
• Two 2 mm e-rings
• Two 2 mm washers
• Five 2.5x8mm socket mind limit screws
• Nine 2x8mm screws
• Thirteen 2x8mm screws
• Six 2 mm peanuts
• Four 3x10mm flanged screws
• Two 3mm nuts
• Four 3x6mm flat head screws
• Two 3x8mm screws
• Three 3x8 mm self tapping screws
• Two gear box halves (black colored molded nylon)
• One trailer hitch (nylon)
• One hitch dish (nylon)
• Two nylon leg guides
• Two nylon swivel arms
• Two nylon mounting arms

Needs:

• One Standard Servo
• Four "AA" size batteries.