We are working on the second prototype of the open source tractor, as discussed in the last post. We have come up with a sketch for the new LifeTrac II frame, which was drawn in Blender. The disks mark the location of the wheels, and the middle verticals will serve as the attachment for the 2 loaders – front and rear. The idea is to come up with the simplest, replicable, design-for-disassembly, lifetime design consistent with our specifications.
We intend to develop this sketch further until we have a fully working 3D model to reference when we come to physically building LifeTrac II in the workshop. The usefulness of Blender is to determine exact bolt locations and sizes of structural members. This is especially useful when designing the loaders and quick attach plates – where we can model the heights and angles required prior to building. You can see our initial designs from over a year ago for reference – on the evolution of the project.
Addendum:
Our experience has shown that it is one thing to make a pretty drawing – but another, much more difficult task to make a drawing that actually represents the device being built. The former is an example of a conceptual drawing, and the latter is an example of a technical drawing. In the former case, one must spend days figuring out how things will actully fit together when building the device, because the drawing does not provide that information. In the latter case, all the figuring is done in the design phase on the computer screen. This allows one to build a particular device in days – as opposed to weeks. The latter case avoids the lengthy process of reworking/taking apart/retrofitting the build – which is so common to the prototyping process. Furthermore, designing something on paper that will actually work requires a lot of experience with the actual building process.
It is important to consider that conceptual drawings rarely lead to replicability. Technical drawings, on the other hand, are the substance of replicability, and turn peoples’ ideas from one-off productions to ones of major, potential, world impact.
Coming up with working, technical drawings is a true art that requires build experience – and we’ve yet to master that at Factor e Farm. This is also why designers who are only designers, and not designer-builders – are limited in their capacity to produce simple, effective, and efficient designs. This is the reason why wrench-turners cuss at the engineers – who insist on designing difficult-to-service devices as a general rule of the status quo.
Civilizations have been known to collapse because they could not keep up with their complexity. It is important to take this point seriously. -Marcin
I recently received a used Caterpillar 226B. It operates on a hydraulic drive train and conforms to a geometry that allows the use of attachments from any of the major skid steer vendors (bobcat, etc.). It seems very similar in principle to the LifeTrac concept except the power unit is not modular. I wondered if you have considered using the same attachment geometry so that you can optionally use attachments meant for other skid steers or apply your attachment designs to other skid steers? I think tractors have a similar philosophy with the PTO hookup.
I’m still learning how to use the machine to it’s full ability, but I have found the following attachments very helpful:
1. clam shell bucket (grading and other tasks are made much easier than a simple bucket)
2. set of forks – there is always something heavy to move e.g. engine blocks, transmissions, etc. and a pallet is an easy way to store/move it
3. auger – it is useful for fencing, but also planting fruit trees, or setting concrete piers
For storage of the skid steer and many other items (I’m using one for Hay), I have found the 40′ shipping containers very useful and economical compared to building the same volume. A 40’x8’x9′ container can be found for under $2000 in decent condition. The 20′ containers are only slightly less money for half the storage space. Just paint with rustoleum or killz oil based primer, and cover the roof with aluminum mobile home roof coating (to reflect back most of the heat).
Ian, thanks for your comment. We are making provisions for adapter plates for other recognized machines. If we assume that there are many different types of quick coupling systems, it appears that the best route for interoperability with other off-shelf implements would be to fabricate adapters that would fit on our quick attach plate.
Thanks for the reply Marcin. I was told that the quick coupling systems were the same among the different skid steer vendors to allow interoperability – but this information may be wrong. Presuming this is true and it is a good quick coupling system, I wondered if it made sense to use the same quick coupling on LifeTrac – hence adapter plates would not be needed.
When I have needed to build something in the past I often try to reverse engineer as much prior art as possible. Perhaps you have already done this, but if you have the access it may be informative to sketch or videotape a minimal tear down of some of the other newer machines (CAT, IR, John Deere, etc). If I lived closer I would gladly offer my CAT.
Some other useful items on my skid steer:
1. Auto bucket leveling regardless of the machine spatial state – maybe this is done with an accelerometer and a PID loop?
2. there is a safety bar that locks down and protects you if e.g. the hydraulics give out while I’m working under the bucket
3. a roll cage over the driver can be helpful since I’ve had a few dangerous moments with heavy bucket loads on the hilly terrain in my area – I suppose this could be a removable option on your design though
4. The controls are two joysticks/flight-sticks and I’ve found this a fairly intuitive design – one for movement and the other for attachment control
5. a full day in it and you will feel beat up – I wish my machine had air shocks or some other dampening system under the seat, maybe even ferrofluid/magnetic dampening? ferrofluid seems like it would be easy to make: oil carrier + Fe3O4
Since you are considering the next version of Lifetrac – I thought I would throw a few comments out on the things I (dis)like about the machine I have, I’m sure you’ve accumulated many more from active use of LifeTracI
Best of luck
Ian, do you have a video camera? Can you document your quick attach system?
One other thing I forgot to mention:
I’ve not done this on my machine, but you can use hydraulics (on lifetrac or elsewhere) as a cheap but fairly accurate scale to weigh heavy objects by looking at the pressure differential in the fluid – e.g. you may want to weigh large amounts of grain, scrap iron for the forge, etc.
here is one of many low tech methods described on the internet:
http://www.caf.wvu.edu/~forage/library/forglvst/wvusite/hydrauli.htm
although a microcontroller solution could produce something much nicer that is part of the tractor control panel
weight data could even improve safety by letting the operator know (or auto correct center of mass) if they are in dangerous conditions based on a feed back loop using 3 axis accelerometers and bucket weight – my machine is a few years old so this may already be a common feature on some of the newer machines
Ian, this is interesting. We already have a quick-connect pressure gauge, and we plan on making most of LifeTrac II with quick-disconnect hoses. We will probably be able to use the ‘hydraulic scale’ to weigh heavy objects.
Marcin, yes I have a video camera and I can document the quick attach system. It may take me a few days, but I’ll post to the wiki when I have it.
Unless you wan’t to use the animation system or game engine in Blender, OpenSCAD might be a more suitable general CAD software for this kind of workflow. It allows exact programmatic modeling. Parametrization is natural, since it’s all code.
It’s very easy to get into, at least for coders, so not much cost in trying. Definitely add to your toolchain.
Elmo, with Blender, we are figuring out the details by being able to observe them visually. The second step is being able to parametrize the frame. How can we use OpenSCAD, which doesn’t have a graphical user interface, if we don’t have the parameters initially? I guess the fine point is that we are not modeling from parameters, but actually designing in Blender.
I did a few quick searches and perhaps you will not need a video. Please let me know if anything is unclear though, and I will still be happy to clarify with a video of my machine.
This thread discusses quick attach, but also provides a dimensioned image of the quick attach plate: http://www.tractorbynet.com/forums/attachments/113183-skid-steer-quick-connect-all.html
This video shows some of the functionality on a newer skid steer :
http://www.youtube.com/watch?v=49Yakrbo6hc
@ 0:20 they show the attach/detach process – on mine there are also two handles that lock down to hold the attachment in place, this appears to be automated on newer models though
@ 0:40 the red bar on the side is the safety bar that I mentioned to lock the bucket in place while you are under it
@ 1:02 you can see the cockpit with the two control sticks I mentioned
I’m posting in two parts since large comments get bounced with no indication from wordpress.
another video, shows quick attach @1:20 : http://www.meyerproducts.com/Portals/0/Meyer/skid-steer/SkidSteer-EOU.jpg
This diagram illustrates the attachment process: http://www.youtube.com/watch?v=cd_Bn9z41Lk
the handles I mentioned can be seen in step 4
this link discusses the history of quick attach, and indicates that since 1994 all manufacturers adhere to the same geometry – there is also another dimensioned image:
http://www.bucketproinc.com/products/universalquickattachsystemqas.php
This video shows the clam shell bucket I mentioned, and how it is used: http://www.youtube.com/watch?v=7VE9eBktQQ4
they also are called “combo bucket” or “4-in-1 bucket”
image version: http://www.attachmentscjj.com/html/combination-fourinone-bucket.html
There are many companies that sell their own attachments to work with this system, this is just one example: http://www.everythingattachments.com/default.asp
Several companies have a track system that fits over the tires. You may want to reverse engineer this if you plan to have optional tracks in the future.
Ian, thanks for the hints on the quick attach. We’ll modify our designs with the new learnings.
[…] last few days we have been wotking on the second open source tractor protytype – LifeTrac II – on Blender. Here is the progress so […]
Hi Ian. Thanks for the info on the quick attach system. I’ve been studying it to try and replicate it so that LifeTrac II can use all Bobcat and other 3rd party attachments but I can’t quite see the way the attachment works at the bottom of the system, where the pins latch/lock the attachment into place.. Do you know of some extra links that show this part? Marcin says you have one of these machines? Could you film/document briefly the locking of an attachment in action?
Best regards