Sat 22 May 2010
LifeTrac II Design
Posted by William
These last few days we have been wotking on the second open source tractor protytype - LifeTrac II – on Blender. Here is the progress so far.
The concept involves:
- front end loader and a back-end loader – doubles attachment flexibility
- 4 wheel drive with direct coupling of hydraulic motors to the wheel shafts
- modular Power Cube power source – 2 can be attached at the rear, 1 at the front
- Driver sits inside – frame functions as roll cage
This frame corresponds to 4x4x1/4″ tubing, with 3/4″ and 1″ bolts for the xyz corners. This is design-for-disassembly. Next steps include converting this drawing into a fabrication procedure – by converting the geometry into a list of bolt locations and other attachment locations. As soon as we have this, we can get the metal and start the build. The next drawing will have 8 inches added to the base width and the hydraulic cylinders will be mounted directly onto the the base frame. At the moment we have a good working height of the loaders – almost 10 feet high.
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May 23rd, 2010 at 4:46 pm
What is the rated load capacity for each of the attachment points, or has this not been calculated? I think it would be important to get at least a rough estimation of what kind of loads LifeTrac II can handle before going through all the trouble of fabricating it. Material can be expensive but calculating maximum capacities is only a cheap matter of time. Just wondering if this kind of thing had been gone through.
Demented
May 24th, 2010 at 1:14 pm
What you’re talking about is engineering. Our engineering strategy is to overbuild for lifetime use. Furthermore, added weight is a desirable feature in a tractor.
We go through baseline calculations only – such as a round figure of 50-100 ksi for steel. Thus, for example, we know that the quick attach plate pins of 1″ diameter will shear at about 50,000 pounds of force. That’s enough for us. One gets a feeling for the correct size after a time, too.
There are areas where more exact calculations are useful. The over-built tractor is not one of them.
The other side of the story, as the local custom fabricator tells us – is that the highly engineered parts fail more on tractors. We’re told that the modern tracter is built increasing ligher in structural members, basically, with the minimum acceptable. That keeps our local fabricator busy with repair jobs.
May 25th, 2010 at 9:23 am
I was more concerned with the safety issue. It only takes one crushed and mangled body to make checking a few things worth while. That said, I agree on most points with you.
However, the failure of engineered items that your fabricator friend talks about is not a failure of engineering, but the end goal. I’m sad to say that they teach us how to make this happen. We almost never, in industry, design things to last as long as they can. If you make a car that lasts 50 years, you don’t sell to many cars. This is what your fabricator is noticing, parts fail at the end of the warranty period. I’m not a huge fan of this sort of engineering–it’s sort of embarrassing professionally that we do this.
My $0.02 is simply that max loads at critical points be calculated so that future user can be warned and know the limitations of the device. Part of making a product is making sure it is reasonably safe for the end user.
The initial design looks promising though. Looks fairly easy to build and certainly easy to fix.
You guys are doing a great job. Keep it up.
Demented
May 27th, 2010 at 11:20 am
I really like what you are doing – building a sustainable, self-sufficient future.
It’s like Jacques Fresco’s Venus Project, only simpler and more realistic.
My father is building small machines for working alone in a forest. As a hobby and for himself.
A great inspiraton is compact tractors made in Sweden “Alstor”
You can check out these from youtube: http://www.youtube.com/watch?v=3HyLsgFdEpU
I would like to see more pictures of how you work and live.
Keep up the good work!
May 30th, 2010 at 7:49 am
Hi,
Your CAD rendering answers some Qs I posted previously, and raises some new ones. By the look of it the revised design is rigid: how will you keep 4 wheels on the ground? I use a CSF Multione compact loader – all hydraulic, btw – and the biggest problem is stability and traction on rough ground, as it articulates but does not oscillate (I’ll be fixing this in due course with a centre rotation joint, with the aim of giving it true off-road ability, something like the Swedish ‘Mactrac’ loader – http://www.mactrac.se). Also I’m assuming it’s a pure skidsteer? I wonder about this in agricultural applications, it’s not necessarily the gentlest or easiest way of manoeuvring on boggy ground….I appreciate the simplicity & strength tradeoff arguments.
All the best,
Richard
ps David (May 27th), if you like the Alstors (I’ve had one working in my woods briefly and they are impressive, if v. expensive) you might be interested in a Swiss home-build at http://www.xcat.ch. Same configuration and some very nice fabrication skills on display.