Sunday, May 15, 2016

M8 Greyhound 6x6 Armored Car

Powertrain: L motor
Steering: M motor
Gun elevation: M motor
Turret traverse: M motor
Controlled by SBrick

This model is one of the more compact vehicles I have built, as the suspension utilizes a majority of the available internal space. The major difficulty when building this model was the mounting of the turret traverse and gun elevation motors. They had to be mounted between the first and second axles, as the space between there was taken up by the battery box and steering mechanism.

Here you can see the basic chassis without the motors mounted for the 

The suspension for the first axle relies on a leaf spring, as there is little available space for mounting shock absorbers like the rear axles. The first axle was the most difficult to work with, as it mounts a M motor for steering.  I attempted to mount the pivot point as close to the center of the wheel, to mitigate bump-steering. The only downside to the steering system is the worm gear used to drive the rack, I would have preferred to utilize a servo motor in this case, as it is difficult to control this vehicle at higher speeds because of the slow and limited steering radius.

The powertrain of this model consists of a single L motor located at the rear of the model, this is utilized to drive the rearmost axles first. I would have liked to utilize two L motors, but because of space constraints I was limited to using one. I am pleased with the performance of the single L motor, it provided enough power for the model to reach decent speeds, but lacked proper power to drive on any rugged terrain. With  two L motors I think the performance of this model would greatly improve, as it would perform similarly to my last MOC, Elvis.

I am very pleased with the shaping of the hull and turret, these areas were rather difficult, as the armored plates are positioned at steep angles to improve the little armor the real vehicle had. The front plating's angle was difficult to achieve, as the steering motor is mounted directly below it. The point where the wheel covers and frontal plate meshes was another difficult spot, as the plates didn't meet at perpendicular angles, so a solution was devised for it to mount at an offset to allow them to mesh. It was also more difficult on the left side of the vehicle, as the mounting system for the SBrick made it difficult to mount the roof of the model and have clearance for the M motor on the left side, as it is raised one stud higher than the motor on the right.

The turret structure was one of the most difficult parts of the shape of the model, a round turret with an exposed interior. As most people know making round structures with the Lego system is a challenge in itself, but making the structure round and hollow, well that is even more challenging. My first attempts were to use pneumatic hoses or rigid hose to create the round structure, but both of those solutions lacked proper rigidity. I finally decided to use #4 Technic connectors to make a ring structure with three stud long Technic axles between each connector, this allowed me to create a structure with eight faces, and an additional eight, if the pinholes were used from the top face of the connectors. I then used Technic bricks to offset the slopes by one-half a stud to create a nearly perfect ring structure will little to no gaps between the slopes.

a close up of the turret structure

I am really pleased with the performance of this model and the SBrick greatly helped improve the handling of it. The customization of the SBrick's control setup allowed me to set the total speed to the gun elevation and steering to half of the original M motor's top speed. This made it easier to make small adjustments that would be more difficult with the Power Functions IR remote. I will defiantly incorporate it for control of the primary systems of a model, the Power functions IR system will allow me to control extra features that don't demand long distance control.


More photos

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