Ripsaw
Simple lightweight model of a high-speed tracked vehicle. Features realistic suspension system
Datasheet:
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.
@benjamin
No. But you can build it from the photos, it’s dead simple.
could you make instructions for the ripsaw please
@technic-master
Very few.
one question how many things did you break in all of lego videos ?
@benhuangua
Thanks. The Chinese edition is already in the works and will be published soon.
hi, Sariel.
there are always awesome works in your site.
i have a question. if i want to translate your book — unofficial lego technic builder’s guide into Simple Chinese version, what should i do?
Thank you. there are lots of fans of you in China mainland and Hong Kong.
@hawk
Thanks. It’s a dead simple model, I don’t think you need a tutorial to build it.
That model is amazing! My friend has the CRAWLER, that stupid truck always destroys me in battle he always runs me over quite literately. O and could you make a tutorial on this? It would be greatly appreciated. Thank you.
@Anton
No idea.
Hi Sariel!
When I saw the video of your workshop, I just needed to ask you this question: How much is your lego worth? It may seem as a strange question, but I was just wondering.
@technicfan
No, it would not. Speed control remote takes ages to get any accuracy, and subtractor is simply not needed here, not to mention it would make the model two times as big.
Why don’t use a subtractor and speed control remote? This would enable sensible steering.
@Witherley
Of course the size of wheels affects the speed and torque. There is a ratio between the wheels and the ground just like between to gear wheels.
@Witherley
This is an edit: Both tanks were also roughly the same size and had 1:1 gear transmission.
I’m not sure where to put this because there isn’t really anywhere specific to put it, but it relates to vehicle construction, but I’m assuming you noticed that the actual size of the wheels also affects the speed and power of the model?
I’ve noticed it when making tracked vehicles. I made an RC tank with very tiny wheels tracks and it was extremely slow. I then made a second one using the 42021 Snowmobile tracks with two 40-tooth gears as the drive wheels and it could go ridiculously fast and even do wheelies because of the receiver placed at the very back.
I’m assuming the reason it went faster is because the wheels were bigger and presumably increased the torque, and also because the wheel can make less of a turn to go the same distance, which when combined with a motor going at the same speed as a tank with smaller wheels would make it a lot faster. What do you think?
EDIT: Both tanks were approximately the same weight.
Good idea, it’s simple and efficient. Maybe you can use it like base to other projetcs more elaborates.
Hi Sariel,
maybe the problems come from the fuse inside the battery pack. The RC motors may take more than 1A.
http://www.philohome.com/batteries/bat.htm