Simple lightweight model of a high-speed tracked vehicle. Features realistic suspension system
Completion date: 25/01/2014
Power: electric (8878 batteries)
Dimensions: length 42 studs / width 16 studs / height 21 studs
Weight: 0.86 kg
Suspension: pendular bogies on trailing arms with shock absorbers
Propulsion: 2 x RC motor geared 1:1
Motors: 2 x RC motor
Top speed: unknown
The original Ripsaw vehicle is what happens when you strip a tracked vehicle of everything except a very basic body, soft suspension and a powerful engine. It’s an attractive subject to anyone interested in tracked vehicles, and having been asked to build it a couple of times I have finally decided to give it a go.
My model was by definition very simple and lightweight. I have used two RC motors for propulsion, but with a Power Functions system instead of the RC unit, which would make the model much larger and heavier. The narrow chassis housed two PF 8878 batteries, one for each motor, and two PF V2 IR receivers in the same system. It was a solution much smaller and lighter than a complete RC unit, and it also allowed simple steering, which would be greatly complicated with the RC unit.
The suspension system was modeled after the real one, including a total of 6 independent arms connected to soft shock absorbers, with a 4-wheel pendular bogie on each arm. The entire system was adjusted to work very softly, which also made it very sensitive to model’s weight. It was quite a challenge to make the bogies strong enough to stay together without losing any wheels, and then I had to make the tracks very tight to stop them from falling off.
The model performed nicely indoors, it had a powerful acceleration and steered greatly, but it felt like it somewhat lacked power to handle any serious obstacles. I was curious how it would perform outdoors, with a nice clean weather and cold reaching -20°C, hoping that the cold would stop the RC motors from overheating. The model turned out to perform nicely for a short while, and then, as the batteries got colder, it would lose all power repeatedly after a few seconds run. This was a bit surprising, as the type of power cells used in the 8878 batteries is supposed to handle the cold well – the same type of a power cell is used in the GoPro camera, which worked flawlessly at this temperature. It remains to be seen whether AA batteries, especially the rechargeable Eneloop ones, which are supposed to work well in cold too, perform any better.
In the end I was rather disappointed in the model. It was tiny, ugly, extremely loud indoors and struggling with the cold outdoors. Still, the suspension system, which was the most complex part of it, worked exactly as intended.