Learn about the GrabCAD Platform
Get to know GrabCAD as an open software platform for Additive Manufacturing
Visit our new homepage
Show off your skills and solve real design problems
The Global Village Construction Set is a platform of is a modular, DIY, low-cost, high-performance platform that enables fabrication of the 50 different Industrial Machines that it takes to build a small, sustainable civilization with modern comforts. It's all open source and for the good cause.
One of the planned machines - LifeTrac is a low-cost, multipurpose open source tractor. What we are looking for is GrabCAD engineers to improve the quick release wheels solution and resolve the failing motor coupler issue. This is going to be a great step forward on LifeTrac’s direction as the world’s first life-size Lego tractor. So your help on this interesting task is very much appreciated.
Current conception of the wheel assembly:
http://opensourceecology.org/wiki/LifeTrac_Wheel_Assembly_Video
During the testing period, motor coupler appeared to fail and stopped functioning.
http://www.youtube.com/watch?feature=player_embedded&v=i4GjoFQ3zsg
The winning design is expected to be a monolitic assembly with motor, bearings, and shaft – that can be taken right off the existing frame – by loosening a bolt and releasing a cam lock.
This simplifies the former mounting method, where 3 mounting plates were attached to individual frame members by using 6 bolts (see the picture).
Also, check out the introductory video of the GVCS project.
To be able to take it off with just 1-2 bolts within 5 minutes.
High-torque, splined shaft motor ghave to be used:
Bolt with cam around bolt, where cam is locked in by a lever and tightening the bolt both fixes the lever and pinches the frame tubing
Cam has a handle running parallel to the shaft when unlocked, and parallel to frame members when locked. Cam handle is welded directly to cam
A second bolt towards middle of assembly pinches the assembly around tubular frame members
A peg (see concept drawing) fixes the assembly in place on the frame. Note that the cam and bolt can be integrated into one, not shown on concept drawing. The second bolt is also not shown in the concept drawing
Cam concept (top view, bolt head not shown)
Complete LifeTrac Frame geometry must be considered as per the downloaded model.
Winning design will be chosen based on the design and functionality
The competition is open to everyone
Team entries are welcome
You can submit several designs
Only models uploaded to GrabCAD library will participate in the competition
Only models uploaded through this challenge page will participate in the competition
Tag your model with “lifetrac” to make it easier to find.
Privately uploaded models will be made public after the competition deadline
Models can be done in any CAD software as long as a STEP or IGES files are also uploaded
Competition starts: 6st of December, 2011
Competition ends: 24th of December, 2011
Competition winner will be announced in GrabCAD’s blog
The entire project is based on open source principle, encouraging people to participate for the good cause.
But there are some nice things we are giving away:
Limited Edition GrabCAD and Global Village Construction Set T-Shirt + Admission to a one-day Natural Building workshop at Factor e Farm in 2011. Includes hands-on experience: brick laying with CEBs and square bale insulation; assisting with lumber production with the Dimensional Sawmill, and square bale making with the Baler. See our Kickstarter campaign for more information on this package.
Most creative design will be chosen by Open Source Technology with a little help from GrabCAD
Open Source Ecology is a network of farmers, engineers, and supporters that has been imagining and creating the Global Village Construction Set, an open source, low-cost, high performance technological platform. These DIY-fabricated industrial machines can be used to build a sustainable civilization with modern comforts. The GVCS lowers the barriers to entry into farming, building, and manufacturing. It is a life-size lego-like set of modular tools that can create entire economies.
Have an awesome idea for this competition? Want to win cool prizes? Sign-up now to upload your entries.
If you don't receive the email within an hour (and you've checked your Spam folder), email us as confirmation@grabcad.com.
35 comments
Marcus over 12 years ago
Halo, I watch your work for a long time now, and I like it.
It will be honor for me to participate in.
Karco over 12 years ago
I like your work very much. I hope you can give the best model for this and anothers machines with the help of GrabCad's members.
I´m sorry because i can´t do anything interesting for you. I only know the wood as material for build a lot of things...
I´ll see your results here, guys. Congratulations for this genial idea ;)
Hardi Meybaum over 12 years ago
The ideas is that everyone can participate. If you don't have very big domain expertise you can still participate because you think out of the box. It's all about collaboration and doing something good for the community.
William over 12 years ago
I watched the vids and read about this project and it is a very interesting project that you guys are taking on. I might not have the right level of education as to the mechanics side of things yet but I sure would love the opportunity to hopefully have some input with such a great project.
Hardi Meybaum over 12 years ago
Nicolas, like to see your work here.
Hardi Meybaum over 12 years ago
Be sure to check out these links as well:
http://www.ted.com/talks/marcin_jakubowski.html
http://blog.opensourceecology.org/2011/12/lifetrac-design-challenge-live-at-grabcad/
marcin over 12 years ago
For those interested in this challenge, we are looking for the simplest possible drive system for a skid-steering tractor which also allows for quick interchangeability of wheel units. This is simple in principle, yet most difficult in practice. There is no industry standard precedent. Considerations regarding the driving force itself, without considering the quick connect wheel mechanism – are:
1. Prototype 1 (http://blog.opensourceecology.org/2008/09/lifetrac-continued/) of the tractor had 4 wheel drive and 32 cu in motors, with articulated steering. The wheel motors are coupled directly to the drive shaft for simplicity. Axial loads are negotiated via 4 double-split lock collars on each axle. Radial loads are negotiated with heavy duty bearings. This tractor has now been in operation 4 years. There is a slip clutch in effect protecting the wheel motors - wheels can simply spin out under excessive load. 16" truck tires have wheel chains here. Each side of the tractor is controlled by a spool valve, with motors on each side in parallel with each other.
2. Prototypes II and III feature tracks. Because wheels and motors are connected by the tracks, the motors sometimes fight each other and prevent proper bypass of pressure spikes in aggressive driving.
3. We have broken 2 motors already on Prototype II – the motor broke internally. In prototype III, we have broken shaft couplers and sheared the shaft key on 3 motors. It appears that the reason is that we ran the motors at too high pressure. We got the motors from SurplusCenter, and these were rated at 3050 psi in the catalogue, and now, the identical ones are rated at under 1200 PSI in the new catalogue. We ran them at 2500 PSI, so we may simply be running the motors over their rating and breaking them.
4. At 1200 rated PSI, the above motors are insufficient to drive the tractor if the tractor uses tracks. They have 1370 pounds of pulling power (total for 4) at this rating. When using tracks, the tractor requires more force to move.
What are possible solutions to the driving force consideration?
1. Use stronger 14 splined motors (8700 in lb), same 2-bearing mounting of shaft, with tracks (to address spinout and provide extreme traction) – with bidirectional pressure reliefs (cushion valve) added to each motor to prevent motor failure if they fight each other.
2. Use stronger splined motors (8700 in lb), same 2-bearing mounting of shaft, without tracks, but 50/50 flow divider (to address spinout).
3. Same as 2 but use stronger motors adapted to 6 spline coupler, with (15750 in lb motors (total 4200 lb of pulling force, comparable pulling power to F250 pickup truck) – advantage being adaptability to existing spline shafts on wheel axles. See http://opensourceecology.org/wiki/Quick_Connect_Wheels#Pathway_5
marcin over 12 years ago
Note on the above Requirements in Challenge description: That is only a suggestion, but it does consider absolute simplicity. We are open to other solutions, as long as simplicity and low cost are present.
Emil over 12 years ago
you could put up 2 keyway.
Your problem is the design it is to heavy, and the distance from the motor to the wheel is 660 mm tray to reduce to reduce the torque
Flaviano Crespi over 12 years ago
Someone can upload the STEP format version of the assembly?
Thanks in advance.
Manolis Theofilos over 12 years ago
No wonder why the single keyway failed. Even in lower torques splined couplers are used. I also have to agree with johny, the motors are too far away from the wheels stressing the shaft for no particular reason. Even if a stronger coupler that doesn't fail is made, it would not surprise me if the shaft started failing due to the torque.
I have some ideas for the wheels but, most of them include cast parts.
Emil over 12 years ago
If you are interested in redesigning i have an idea (reducing weight by 25 - 30%).if not i can reduce the torque but i don't know whit how much and i can tell you how to build the new parts, just tell me what you want to do.
Zach Pickard over 12 years ago
Hey guys, I've posted my initial stab at the monolithic mounting system feel free to grab my design and modify it if you're looking for a starting point. I've been running through the torque problem and here's what I've got so far.
As Marcin posted above about the 15750 in lb motors, I believe that if you can find a torque converter that fits the dimensional requirements and install it only to the front or rear axles it will solve the problem of the motors fighting each other. Alternate which axle the torque converter is mounted to on each side (ie. front left and right rear axle) so that way you have a fixed motor on both the front and back of the tractor for either lifting or pulling heavy loads.
Another solution might be to develop a spring loaded torsion damper like used on some shaft driven motorcycles. This would have to be massive to accommodate the amount of torque these motors have though. I'm throwing all this information out there hoping that someone might be able to develop something that works.
Chris Duncan over 12 years ago
If the wheels are connected by the track chains then why do you have to drive all 4 of them? Why not just drive 2? Not positive but I'm pretty sure a normal tracked vehicle only has one drive wheel per track.
you need to extend the deadline, you are competing with other challenges and don't have as much time.
Chris Duncan over 12 years ago
One drive wheel per track would mean that drive would have to be stronger but it would simplify things with less parts and end the torque conflict of 4 drive wheels.
Martin Camirand over 12 years ago
The torque is well documented here, but regarding the total weight of the tractor, including driver, poer units, tool and load (bucket full) do you have any idea how much all this can weight ?
Thank !
(gonna try to give this a go in the next days.)
Martin
Zach Pickard over 12 years ago
@Chris,
Marcins comment above says that after they blew out their motors running them at 2500 psi they cut the pressure back to 1200 psi and they were only producing 1370 pounds of forward pulling power. He mentions that the tractor wouldn't move on it's own like that. 4 motors at half power isn't enough to move the tractor, half the motors at full power won't work either. And like you said, the drive shafts would have to be much stronger to support that much torque on two axles instead of all 4. I'm not saying that it won't work, just that you're going to have to get bigger motors and drive shafts. :)
Zach Pickard over 12 years ago
One other thing to consider. If the wheels aren't going to be tracked all the time, only having two drive axles (and no suspension) means you run the risk of getting stuck in a rut or high centered much easier.
Emil over 12 years ago
yes but my idea is all ready applicably to the tractor
The model is build just need the modification to be functional
And the torque is a lot smaller .
maybe it will work wit 2 engines but i don't know the exact mass
it approximate some around 1.8t
Martin Camirand over 12 years ago
I took a moment to look at the shaft dimensions to be able to sustain the new motor hight torque (11 000 lbs-in = 1250 Nm).
I took the shear stress formula wich is : S=Tr/IP (S=stress, T= twisting moment, r=shaft half diameter, IP=polar moment of inertia)
Knowing the polar moment of inertia for a solid shaft is: IP=Pi*d^4/32
I move some term to obtain this new formula:
D= (T/((Pi/16)*(Selas/SF)))^(1/3)
where D= shaft diameter,T= morto torque, Selas= elastic limit of the material used and SF=safety factor.
If we assumed the material used is steel with a 350 MPa elastic limit, we set a safety factor of 3 because we need a robust design, The motor torque is 1250 Nm.
This give us a shaft diameter of 0.0391 m or approx 1.54 in.
Martin Camirand over 12 years ago
.IGS file or .step file would be great, I have acces to CATIA, PROE or NX but not solidwork. Thanks
Martin Camirand over 12 years ago
If anybody need the CAD file for the hight torque motor I've reproduced it with the data from bucher hydraulic.
So if you need it it is a .iges in my CAD uploads.
Martin
Martin Camirand over 12 years ago
Ouais en effet, j'avais pas prit cela en compte, j'avais juste fait le calcul pour le couple. ahhhh le MHB quel merveilleux ami ;)
Robert Guyser over 12 years ago
Extremely cool.
Chris Duncan over 12 years ago
Marcin has been featured on Huffington Post
http://www.huffingtonpost.com/2011/12/19/wiki-diy-civilization_n_1157895.html?1324310724&ncid=webmail7
Eric Kauffman over 12 years ago
Uploaded a version of an axle assembly based on your requirements. Love the project you are working on and I am honored to assist in any way I can. The weldment uses a slot and tab design that we use to make large weldments for machining off-highway equipment components that my company makes for Caterpillar and John Deere. in my design I opted for plain bearing over ball bearing based on the load, force, and torque you are applying to this machine. The plain bearing sets are commercially available and much easier to deal with as you have limited machining capabilities. This should eliminate a lot of your issues with bearing and shaft alignment. These bearing are high load plain bearings that are made from Oillite therefore they will never need lubrication. I am still working through the coupling issue. You are putting a lot of torque on this coupling and direct drive although easy leaves you with a number of other issues. I will continue to work on this issue. Good luck!
Kaspar Kiis over 12 years ago
Thank you all for your entries and effort. We will come back to you with results and comments shortly.
Kaspar Kiis over 12 years ago
The results are out now. Thank you to everybody participating in the challenge and sharing your ideas. Open Source Ecology was very happy about the results. There might be similar challenges to come...
Please log in to add comments.
Log in