Hi
I'm building a autonomous robot(university project) that should navigate on a corn field. Our team doesn't have any RC knowledge so help would be appriciated.
It will resemble that
http://autsys.aalto.fi/en/FieldRE

Basic structure
Four wheel drive, four wheel steering
One motor+steering servo per axle
Custom stiff axles
Drivetrain(one axle): RS540 - planetary gearbox - gear - Team Xray XB9(1/8th scale) center differentialIt will go quite slowly (max ~1.5m/s =5.5km/h) and be heavy (15-20kg)
We will have to shorten the dogbones(differential won't be mounted on the centerline) We want tight turning circle and crab steering
Wheels will probably be custom made (milled plastic+glued tread)

We need
Steering knuckles
Wheel axles+hex nuts and dogbones

Requirements
Knuckle with no camber, it will look funny and make our instructor unhappy. We are trying to keep it simple so no caster blocks.

Which 4WD RC car front axle should we use?

I started typing some suggestions....then notice the weight requirement. 40 pounds is a heavy rig.

It sort of seems like you want a MOA (motor over axle) setup, but then you mention the Xray diff? Are you looking for a shaft driven axle, or one with the motor and gearbox on the axle?

Suggestions for either:
Kyosho mad force axles. The newer brushless version of the truck has very tough axles...and I believe the front/rear are the same with the rear having steering lockouts....so you can take them off and mount a servo for 4ws. You will need a very high turn motor, with very low gearing at the center diff and will likely need to run 11.1v 3s lipo to haul that much weight. Those axles are meant to handle a 1/8 scale brushless system on 4s lipo and speeds reaching 45mph. So going slow and hauling a lot of weight, they should be able to handle it.

Exceed mad torque. This is a MOA axle rock crawler. Each axle has a 60 turn brushed motor, low gearing and can steer. I have this truck and it is modified with a large body and weighs 12 pounds. I recently did a pulling test with it. On pavement, I could pull a milk create with 40 pounds of weights in it. This was dragging the weight and running a single 7.4v 2s lipo battery. With 3s, it could have pulled a bit more. If on top of the axles, I am sure it could handle 40 pounds. The axles have 17mm hex's. The internal gears are all metal, and the axle housings have proven to be pretty tough. That said, 40 pounds on top is still a lot of weight.

There are much higher-end MOA axles....some with metal axle housings. These could handle the weight even better, but are much more expensive. A set of exceed mad torque axles is around $90. The whole truck new is about $200.

Thank you for your input.
Not so sure about the terminology but the picture should clarify the axle configuration.

So we are not using the center diff at the center. Two center diffs act as front/rear diffs because pinion gears are easier to work with than bevel gears.
11.1V 3s turnigy lipos have moved the beast in the past.
We are doing our own aluminum frame and axle housings so mainly interested at strong knuckles, wheel axles and dogbones for the wheel axles.

AH, I thought you were looking for a complete RC axle. What you show in the picture we would consider a MOA axle. Each axle having its own motor and gearbox self contained.

The steering knuckles on the kyosho mad force kruiser ve may work. they are cast metal. the axle's driveshafts may also be usable for your goal.

the RC4WD Bully Axle has all metal MOA axles. Again, the steering knuckles/stub axle/hex and driveshafts may be usable.

the very common and popular Axial brand crawlers have plastic axles housing....but there are metal upgrade steering knuckles available. If you used them then axial driveshafts, stub axles and hex's could be used. There are also axle wideners available for their trucks if you wanted to make it wider.

I think most 1/8 car or truck steering knuckles may have caster built in. But 1/10 or 1/8 scale rock crawler knuckles (or upgrade metal versions of them) may give you what you are looking for.

Axial wraith
Axial SCX10
Kyosho mad force
RC4wd

Look up those models plus steering knuckle and see what pics come up (google search) If you see one the shape/style you like you should be able to find a metal upgrade version of it. Then the stub axle and wheel hex for that model can be used, and maybe the axle's driveshaft as well.

Kyosho mad force is 1/8 axials are 1/10, what is the size&strength difference in real life?
I'm especially concerned about wheel axles and driveshafts(shortening won't make them any stronger).

Are CNC parts much stronger than cast aluminum?

YES in some cases can be quite drastically stronger.
CNC'd parts are usually made out of a higher quality aluminum too.
I have cast aluminum parts you can bend by hand, and CNC'd parts 1/2 the thickness that need over 300lbs of force to bend.

wow, what cast parts can you bend by hand!?

but yes, usually CNC parts are stronger.

the axial axles could be nearly as wide if you used axle wideners. but in stock form, the are at least an 1-2 inches shorter.

But, since you mainly want to use the steering knuckles, the width of the actually axles shouldn't matter much. You can make your axle case the length you want. Even tho they are for 1/10 axles, if you go with CNC parts then the steering knuckles of either the kyosho or axial should be strong enough for the job. The stock stub axle and wheel hex's of either truck will handle the weight.

DF-02 aluminum front shock tower. It bent after 1-2 bumps I bent it back with my bare hands, and I am by no means very strong. Its one reason on that model when me and others who own the vehicle say ge the aluminum tower to trace it onto another piece of aluminum(or get carbon fiber), and make a shocktower sandwich as when it bends it will break a bulkhead.