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Gama Goat

October 9th, 2023 Leave a comment Go to comments

Model of an offroad vehicle developed for US Army. FeaturesĀ  6×6 drive, steering, articulated chassis and suspension.


Completion date: 26/09/2023
Power: electric (Control+)
Remote control: Control+
Dimensions: length 46 studs / width 19 studs / height 18 studs
Weight: 1.644 kg
Suspension: double wishbone
Propulsion: 2 x C+ XL motor geared 2.33:1
Motors: 2 x C+ XL, 1 x Spike L

Gama Goat, or M561 Gama Goat as it was officially called, was US Army’s response to the difficulties in traversing Vietnamese jungle. Where standard trucks struggled, this articulated and amphibious vehicle worked just fine and became renowned for its extreme cross-country capabilities. Over 14,000 units were built and remained in use until 70’s, when high maintenance costs made the US Army replace them with more conventional vehicles, including Humvee.

The vehicle was quite unusual as its chassis was split into two pieces. The front part sported 4 wheels, place for a driver and one passenger, and engine bay. The rear part included just 2 wheels and was entirely occupied by a cargo box accessed via a rear ramp. The joint connecting the two parts worked like a live axle joint, that it is allowed up/down movement and rotating along the longitudinal axle, but not turning to sides. The vehicle was steered by turning the wheels on first and last axle. The body was made entirely of aluminum, making it one of the few military vehicles that could be punctured with a knife or even a sharpened stick. Interestingly, the vehicle was just as unreliable as it was unstoppable – the official requirement of driving 32,000 KM in the field tests without breaking down has never been fulfilled by it.

My model was inspired by the need to test several new LEGO pieces, including the Control+ XL motors, the 5 studs long CV joint and the heavy-duty sliding CJ joint. In order to keep the model 17 studs wide, as dictated by the scale, I’ve used live axles in front and rear, and trailing arms suspension in the middle axle. This was V1 chassis and it performed well until I added more weight to it, at which point the torque effect started to heavily tilt the body sideways when starting and stopping, impairing the steering system in the process. I was unhappy with it, so I’ve kept the body but rebuilt the entire chassis from a scratch using double wishbone suspension, which negates the torque effect. The result was that the total width of the axles went from 17 to 19 studs, so in order to at least partially hide this I made the body 18 studs instead of 17 studs wide.

The chassis was driven by two hard-coupled Control+ XL motors. I had a hard time finding room for them until I eventually used them as stringers between front and rear axle – their shape made them work perfectly for it. Due to limited space, the steering was controlled directly by a Spike L motor with a driveshaft going through it. I couldn’t get the LEGO Powered Up app to handle such direct steering correctly, so I eventually resorted to using the third-party Brickcontroller 2 app, and it worked flawlessly. The first and last axles sported open differentials, whereas the middle axle used a 28t gear instead.

For the body, the reasonable choice would be to build it using studless pieces to keep it robust, but I liked the little details too much and went with System pieces instead. In addition, I’ve spent too much time looking at plastic Gama Goat kits in US Army olive drab no. 3 color, and I came to the conclusion that my model needs body in dark tan. This was a color I’ve never used before so extensive shopping followed, at a massive expense to my LEGO budget, but I kept thinking of it as of investment because I’d like to re-use this color in the future.

In any case, the model ended up combining quite solid, well-performing chassis with an extremely fragile body, so driving it was fun as long as you didn’t mind body parts falling off while negotiating obstacles. In the end, the model provided me with a lot of satisfaction, crippled finances and a promising new color for my future military projects.


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