Hi Mat,

I was a constuction engineer in the Australian army, and have mates in the earth moving business so I've seen my fair share of machines using pneumatic tires and tracks, and both have their place (especially in tactical construction). Yes tractors and earth movers can use pnumatic tires, generally quite
large (as the machines are large too) and designed for traction. But that wasn't my point, the point is you choose which one is more appropriate and stick to it. Tracked machines don't generally have good ground clearence, pnumatic tired vehicals generally do. You never see pnumatic wheels driving a tracked vehical, rubber tracks yes, but those rubber tracks are still driven by all metal sprockets.

I also thought that a three sprocket system might be the better option, two load bearing idlers and one driving sprocket which would sit above them. I don't think you can reuse the current chain and rebar track, I've been running over that in my head, and I think it would be difficult to get it to work. For one the chain is currently welded on the end of the rebar, which is bent, so trying to drive the chain would be impossible in its current location. But I don't see that it's a worth while excersie. For one thing manufacturing a sprocket to drive stock chain, I would think, to be reasonably complicated but the real problem I see with the current tracks is there is very little side load stability. Imagine if the LifeTrac had to travel along the side of a hill, what's preventing the wheels from slipping sideways on the tracks? Just the bent rebar? What happens then when the rebar punctures one or more tires? Things could get dangerous very quickly.

The design of my tracks cators for that side load by the angle iron locking on each side of the idlers, which prevents the idlers (or drive sprocket for that matter) slipping sideways.

Well done team for all that you've shared on OSE.
I'm really supportive of open source, these are constructive comments, to help move the project forward, although they discuss current flaws.
I'm keen to build a tractor, I like the idea of long term adaptability and maintainability.

• Current imperial dimension plans & designs are unuseable in most of the world.   Most places use metric, and often only metric steel stock and tooling are available.  Are there thoughts around metric? This will no doubt alter a lot of the force angles, calculations, jigs, templates, kitsets etc.  The materials list makes my head hurt with all those fractions. Your 4" standard is 101.4mm for me, for which the second hand steel dealer will offer me 100mm x 100mm box section. It would seem difficult to turn your plans to metric after you've finished all your research & development.  Remember the mars probe that crashed?

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• There doesn't seem to be many triangles in the grid design of the main frame.  Only the bolts and connections appear to be stopping it twisting in x,y,z axis.  What have you found in testing?

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• Skid steer is just too blunt on the ground for many applications.  It rips up bitumen, scuffs stones, wears rubber on concrete, tears up turf and just generally makes for a very jumpy ride on any hard surface. Most people I know are very happy when the messy & noisy skid steer loader finishes the job and leaves site.  Is the pivot steer design dead? Is steerable front wheels doable? Coarse steering makes subtle movements difficult in lifting applications.

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• I've never seen a skid steer loader with the wheels that far apart, they're always close together, for easier turning. Often you'll rock on to two wheels when changing direction, to make the turn easier and faster. That's not possible with the wheels so far apart.   That means LifeTrac is working more like a scrub steer bulldozer, which is an even clumsier tool than a skid steer loader. Dozers generally need to have a lot of weight to be safe, effective and useful.  This is a long way from the finesse of a wheeled tractor.

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• A bulldozer with a front end loader is a traxcavator. Slow, clumsy, tools requiring powerful engines to be effective, in common use before back hoe excavators.  Now only accepted as useful in specialist applications such as loading & mounding in difficult ground conditions like raw quarry pits and hot steel slag heaps. Search for traxcavator and check the images tab.  Hardly a new or modern one to be seen, they're all retired, in secondary lives or vintage.

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• LifeTrac development seems really focused on improving front lifting application, not much on agricultural 3 point linkage application.  Will this continue to be the focus? Or is this just because you're doing a lot of fabrication at the moment, and will move onto farm work later? Or is it just the selection of video's you've made?

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• Has energy efficiency entered your calculations?  Tracks & skid steering is energy inefficient. Excess tare weight is inefficient. Hydraulics while adaptable are a lot less efficient than direct drive. Motors working hard because they're too small is also inefficient. Energy efficiency is usually a critical design factor, and even more important in poorer parts of the world than America. Efficiency is sometimes traded off for gains in other areas, but is this the case with the LifeTrac? Your design list aims for the tractor to support a 40 acre farm, so that's a lot of tractor working hours, so thats a lot of scarce and expensive fossil fuel, or precious and time consuming to make ethanol.  I can't see how you can fundamentally rework so much of your design for more efficiency, when the whole layout depends on your skid steer and hydraulic function.

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• Tractors have been in development for more than 100 years, and an awful lot of lessons have been learnt, careful thought applied, and alternate designs tested and failed. Millions of man hours and dollars. LifeTrac has lots of good ideas, but doesn't seem to draw on much good knowledge in the tractor or manufacturing fields.  It's like your starting again for no really good reason. A good example is the kinked boom on the lift arms. Dozens of front end loader manufacturers have tried straight, then moved to kinked. It's well known, it works. It's unavoidable physics and angles.

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• For the type of lifting you're doing in a lot of the videos, an overhead boom would seem more appropriate.  Hinge at rear top, hydraulics in middle, hook out the front, no bucket.

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• Some older ideas on overhead booms found on tractor cranes  http://www.hcvc.com.au/forum/YaBB.pl?num=1264161200/9   A lot are still in use in fabrication shops. They're fore-runners of modern telehandlers in some ways.  Many laughs for ugliness, applicable lessons in what not to build.  Form follows function, elegant designs often work especially well.

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• Would a redesign or alternate machine or variant, still using many of your design principles such as simple 4x4 construction, universal power pack, common connectors etc but on a two horizontal-rail more like a tractor design be feasible?  Sometimes more can be learned or achieved from completely throwing away an early design.

Hopefully contributors can answer some of these issues, and I hope they help. 

@DaveMC - All your points are completely valid and quite obvious when you start looking at the current design of the LifeTrac III at any depth as you have Dave.

Hey Matt, sure that's a great idea. It's quite a bit more complicated than that and you need to get into some heavy electronics. If anyone wants to start down that road they're more than welcome to! Personally I'm going to be focusing more on just the mechanics of design and making it work with the powercube for right now and sure once the electrical system has been figured out I"m sure there will be enough real estate to convert it to electric!

Yep, that's the one I was going to use on the LifeCat and was going to be contacting the creator next week actually!

Hey Mat, glad to see someone is reading the crap I write!

Regarding EV Tractor, after building my brick machine, I'll be seriously looking into this. If not a tractor, at least a loader of some description. The main problem with all electrics (as I eluded to in the CEB thread) is the linear actuators. Electric linear actuators of sufficient size for a tractor are difficult if not impossible to find, and if you do find them they are very expensive compared to hydraulic.

Probably the easiest EV Tractor would involve an electric drive line and electric hydraulic pump.

Redesigning LifeTrac?  Check this out:  http://www.skidsteerhistory.com/How it began.

@ Matt_Maier :  Good point to assess Lifetrac in context of GVCS.  You said, however, in an earlier comment that the current LIfetrac design is a dead end. I thought that meant Lifetrac is just a poor design regardless of whether it is being compared to Bobcat.  I'm sad if that's true.  

"You said, however, in an earlier comment that the current LIfetrac design is a dead end."

> I meant the way the frame is built. Bolting together tubes is great for prototyping; not so great as a permanent design choice. No one ever needed to demonstrate a tractor frame. It was the performance of simple/cheap motors, bearings and the power cube that needed to be demonstrated. As the design is refined it will most likely go through at least one major redesign of the basic structure, abandoning the bolted-together-tubes approach.

> I agree that the "tractor" is really a Bobcat. Most likely a design iteration will include increased modularity so it can be changed from a Bobcat type layout to a tractor type layout. Skid steering was merely an easy first approach.