Is it possible to build a 4WD system using three differentials much like a real 4WD car/truck? Should I modify the differentials so that they’re limited-slip? What can I use for joints between the front axles and front wheels so that they can steer? What about parts for large R/C cars/trucks?
i dont know nothin about differentials but the front steering is kind of easy
but if the front wheels have motors its kind of hard
but on 2wd cars i’ve seen a loose point and a motor connected to a rod that turns both front wheels at the same time maybe with some luck you might be able to modify that;)
Front axles on real vehicles usually have CV joints instead of universal joints. I tried to use u-joints from Lego building sets but they break easily. I searched the Internet for web sites related to large R/C models but I’m afraid of wasting money on u-joints that don’t fit and/or break. Would it be easier buying a large R/C 4WD car or truck kit and modifying it for VEX electronics?
im not sure but if you dont mind spending money it would be worth the effort
i want to modify this old rc car i have(its 2wd:D ) to vex
i was gonna hook the back to vex but the motor has 3 wires white blue and black which is confusing to me whether blue or white is the postive 
best of luck if you do try it should be fun:D
I think that on R/C models, the motor is connected to a speed controller and the speed controller is connected to the R/C receiver. I think that the speed controller has five wires - two to motor and three to receiver.
^Thats how it is on my RC car.
http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJD72&P=0[http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJD72&P=0
They are a bit of a pain to assemple need 2 pairs of needle nose pliars…
drill the center hole out just a fraction larger or sand down your shafts a small bit.
these have provided me many happy hours of work. and they are cheap!](“http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXJD72&P=0”)
The VEX shafts fit the Traxxas U-joints without having to drill bigger holes or filing the shafts to fit. Do they ever break even when you’re using two pairs of needle nose pliers to assemble them?
I tried to build the rear suspension system but the results are not good. The wheels are not vertical to the ground and the shock/spring assemblies are not strong enough to support the weight of the chassis.
can you post a pic?
are you saying that you wheels look like
/----\ or \ ----/instead of |----|
and yes you can break the trazzas ujoints if your not careful. but once assembled you don’t have a need to take it apart
The wheels look like this: /-----\ and I broke a U-joint while assembling them. I added more flat bearings and they almost fixed the wheel problem. BTW, some wheelchairs have wheels looking like this: /-----\
the /----\ chamber on a wheel chair is designed that way for a few reasons… i often wondered about that myself but my quadraplegic friend helped me understand why they vary so much. he gave me a few reasons. one is a stability when cornering. he used wheelchair races as an example. basketball players use a little less chamber mainly for manuevuring. and their front wheels are closer to the rear wheels as well. the ones at the hospitials are userfriendly with the |—|. he also says that depending on the indivual it makes it easier to wheel them selves faster when you chamber the wheels out like racers.
now about your structure system on your design. are you trying to memic the “A” frames that automobiles use? or would a better design be similiar to a motocylces rear forks?
so anyway it’s something to think about. i’m not saying that it’s going to be impossible to make the “A” frame setup because with the right equipment you can make it it just is way out in expert field. anyway i wish you luck and hope to see pics
hm… flipping thru the maitenince manual for my truck, i have a couple of diagrams for the rear suspension for dodge RAM, Dakota and Durango leaf-spring set up, for 2WD and 4WD, year 1997-2000. if you want, i can scan the diagrams and post em for you.
the U-bolts come down and embrace the axle, and connect to the spring plate, which connect to the shock (in this case, hydraulic). the rear of the leaf spring connects to the shackle, which in turn plugs into the mounts on the frame. this isnt needed in the front, as the mounts sit low enough to allow the spring to rotate.
you might try crafting a stabalizer bar. the retainers connect directly into the axle, and plug into their spots on the frame. it could straighten your wheels up (but, getting parts like that could be very hard… being that they need to be a certain size…)
as for multiple differentials, heres a couple of pics of a shifting robot:
its built by Bobby C, and has 2 speeds*. you could incorperate this design and use it for the 4-HI (average speed/pulling) and 4-LO (slow speed, max pulling) settings, and even take it further by sticking a 2WD setting in it.
i may talk the talk, but i sure dont walk it. some of my data may be incorrect, but im just trying to lend a hand. truth be told, ive had my vex kit open for about a week, and its the most robot ive handled in nearly 4 years…
*giving credit where due.
Some wheelchairs have small front wheels. I thought that they don’t work on rough ground. I’m trying to create independent suspension system but it’s hard to cut the shafts. It’s easy to cut sheet metal.
heres a small, but somewhat helpful wikipedia article. you might try to manipulate the long, flat bars into a sort of wishbone (or make one from scratch…), and set the motors there, then have it come down like a swing-arm from the frame, using the shocks to keep the chassis up, and the springs to allow motion.
heres a link to a pic of a IRS like system. its the suspension part itself, complete with a translucent wheel. it could help you out with your project. (im simply linking to the image, because its HUUUGE, and some people arent fond of a screen stretch.)
im actually wishing i had a decent hobby shop around here, because id go out and get the stuff needed and build one myself… i do hope im being of some use… i cant do hardly anything with my bot at the moment, due to a lack in funds and no where to get compatible parts, not to mention a lack of a machine shop to craft components from scratch…
down in my area theres a place called hobbytown usa
well i didnt get the vex there
but this one rc car had nice rear suspension the two rods to the motor and still turned the wheels when flexed:D
not sure if i can really explain much this was 4 days ago and i dont remember much
Junkie2.0, where does the chassis from the image come from?
the image came from www.thyssenkrupp.com, however, i misposted the data a bit, and the image is infact an independent system for the front axle on a truck. ill look around some more, and mebbe ill find some good diagrams… speaking of which, heres the rear suspension and drive setup from an old DAF-33:
http://cache.jalopnik.com/assets/resources/2006/12/daf2.jpg
well, not really a diagram, but you can see the springs and drive system nicely…ill keep looking, and post my finds.