Model of a high-performance tracked vehicle. Features complex suspension system and a cannon.
Completion date: 19/07/2014
Power: electric (RC unit)
Dimensions: length 70 studs / width 33 studs / height 22 studs
Weight: 3.15 kg
Suspension: pendular bogies on trailing arms with shock absorbers
Propulsion: 4 x RC motor geared 3:1 from slower output
Motors: 4 x RC motor, 1 x PF M motor
With custom-built, heavy-duty tracks tested in my Grassgrinder, and four RC motors available, the next logical step was to build a Ripsaw. I have already built a small one a few months ago, but this time I wanted to make a serious model.
The model was equipped with two 150-studs long tracks, including 900 2L beams total. This means that the weight of tracks alone was close to 1 kg. Suspension system was made as close to the real one as possible, with pendular bogies housing four small road wheels each, suspended on trailing arms with shock absorbers. The resulting suspension was hard, but worked well. It seemed to transfer more vibrations to the hull than was the case with the Grassgrinder, perhaps because of the smaller road wheels and shorter bogies. The real Ripsaw comes with track pre-tensioners in the front sprockets – here, I have mounted the front sprockets on beams that were slightly bent downwards. This was simpler and stronger solution that using shocks absorbers, and it was able to reduce play in the tracks effectively, but to a limited degree.
The propulsion system was the same, with the same gear ratio, just more motors. The front RC unit controlled the steering, engaging four PF switches with its steering output. The rear RC unit controlled a PF M motor with its auxiliary output, which allowed to include one extra function: a cannon popping up from the upper hull.
The performance proved problematic, once again proving that RC motors are simply not fit for vehicles this heavy. I have put brand new Energizer batteries in the model, and all was good and well for about 10 minutes, then the performance started deteriorating quickly. The hot weather was additional issue, as both RC motors and RC units are known to generate plenty of heat, and it didn’t help that their black cases were exposed to strong sunlight. Every now and then one of the RC units would simply shut down from the heat, and I had to let it cool. This raises questions as to whether it’s possible to include a cooling system in such a model, perhaps in form of a ducted fan.
In the end, the performance was pretty satisfactory, but for a shorter period of time. The suspension worked nicely, although it was perhaps a little too hard – then again, a softer suspension would create plenty of play in the tracks. The propulsion system generated much more torque that in the Grassgrinder – it was possible to make zero-degree turns, even in short grass. The conclusion is that the design was correct, but it was crippled by characteristics of the RC equipment, such as the sensitivity to heat and enormous power consumption under strain.