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Installing a 645mg throttle servo???


Hello eveyone,

I have never installed a throttle servo.......Any tips or how to hints will help ...its a hitec 645 mg going into a rampage mt witha TGN kill switch installed>




One of the reasons why more hobbyists generally change servos is poor quality of the stock servos which are usually underpowered for their purpose. This is more of a problem with steering in Monster Trucks, where a lot of force is required to turn the wheels due to their larger size and weight. One very popular aftermarket servo is the Hitec HS-645MG, which offers good performance for a very cheap price (compared to other aftermarket servos). I decided to use HS-5745MG for steering and the HS645MG for throttle and brake in my RampageMT5.

The two Hitec servos came in small individual boxes, containing the servo and a bag of accessories. Inside the bags of accessories were 4 servo horns (of different shapes and sizes), 4 rubber servo mounts, and 4 long silver screws and washers for the servo mounts.

The Hitec HS-645MG high-torque servo you picked provides 9.6kg/cm of torque (at 6V) and travels from 0-60 degrees in 0.2 seconds (at 6V. It is an analog servo, which means that it will suit nearly all radios.

Installation is extremely simple for this truck and requires very little time. Unplug the stock servo from RX. Removing the stock servos only requires the removal of 5 screws. The new one dropped in easily and screwed tight in no time. The part that most people overlook, however, is that the Hitec servos need different servo horns than the stock servos use. The Hitec throttle servo uses a 24-spline servo horn (#85058-18) It uses the same screw to hold the servo horn on as the stock servo did.

Center the servos. This is done by turning on the power to the servos, and fitting the servo horn 90 degrees perpendicular to the servo. I then tightened the horns with the appropriate screw and turned the power off. The horns do not have to be perfectly perpendicular, as this can be finely adjusted with the trim later on. I also checked the linkages, to make sure that they were moving smoothly. The Hitec servos move in the opposite direction to the stock servos, so you might also have to reverse the direction of the servo (using the switch on your transmitter).

I noticed a huge improvement in power over stock servos. The brakes were stronger and there was faster throttle response with the new servo. This servo made the truck much more controllable. I did notice a big difference in reciever battery life with the new servos. Get a 4700MAH 6V battery. Thanks to these servos, my truck now handles better than ever before!

The Hitec HS-645MG is perfect. It greatly enhances throttle / brake, but does take much more battery life than the stock servo. The HS-645MG is very high quality, and should last you a long time. Coupled with a low price and a lot of power, this servo is hard to beat!


Well-Known Member
Chandler, AZ
Great write up. I chose to take the servo aluminum plate off and work on it off the truck.


Junior Member
Thanks I thought I installed it wrong because it was working in reverse but won't throttle open all the way up instead of applying brakes when failsafe activates if u reverse the controller how do u fix this problem. .......... I know I know kill switch

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