Propject 4ws (4 wheel steering)

[Steve]

Originally posted by frizzen
... But the one thing I'm having trouble with is how you're going to wire your steering motors.

I hit LEFT on controller, the front axle throws LEFT, the rear axle throws RIGHT? Or if they both throw left wouldn't that make the turning radius either absurdly huge or nearly non-existant, but it'd be better for high-speed running.

I ran the two steering motors off the same place on the PCB. SO, turning left means the front wheels turn left, and the rear wheels turn right. It shortens the turning radius dramatically, which is what it is supposed to do.

[Steve]

And that was that. I put the electronics in, the body on, and went for a test drive. What I found was somewhat disappointing. While the truck certainly turns really well... it somehow lacks something I thought it would be.

The paltry little spring suspension on all four wheels is pretty much useless, much like it is on just the front. Maybe softer springs would actually work better, but there's bigger issues anyway.

Power. Much like the stock version of the truck, it lacks power. I even put three cells in it, but while fast, it still doesn't have the power it needs, which means I really need to gear it down, waaaay down. But there are other issues.

Gearing. Moving the drive gears into the center and away from the wheel has seriously compromised ground clearance. AND there are still more issues.

Stance. I had to widen the stance so that the tires would not rub on the gears. Good for balance, bad for ground clearance as it now cases on each and every little thing.

Run time. Seriously compromised with two steering motors.

I guess I thought 4WS was the "holy grail" of mods. I was stoked about getting it to work, but it doesn't really enhance performance any. Sure it turns well, but in all honesty, I get more satisfaction out of turning badly and plowing into and over everything in my path. This truck won't do that because of the issues listed above. It would require relocating the drive gears, adding more batteries, gearing way down, and articulation, to even come close to the performance gains you get from articulation alone. Gearing down and adding articulation to a stock truck almost instantly makes it a rock crawling beast. While I certainly won't say it was a waste of time, the minimal gain doesn't even come close to justifying the effort put into it.

So it's back to the drawing board, though perhaps with something to build on. Much like the problem of [driving] the truck was a hinderance before, it still is. Moving the drive gears up is no good because of space constraints within the body. The only solution I can see would be one of multiple smaller gears, but then space between the wheels is still an issue. Pullys, worm gears...maybe. One thought I think I came across on here was using a servo or stepper motor for the drive motor. Stepper motors usually have mad torque and are very slow....two things I need in a crawler. Maybe big gears wouldn't be needed at all?

thoughts?

[frizzen]

I do NOT mean anything against yours by posting this, but check out what this guy did.

http://549.rapidforum.com/topic=100379626552

Sorry, it IS german so you might need a translator

[Steve]

Absolutely no offense taken...that's AWESOME! German engineering rules! I attempted to build mine using as many ZZ parts as possible, but it's obvious what can be done if you're willing to fabricate a little. At this stage, we might as well just toss the whole chasis out the window and build it (right) from scratch.

What did this guy use for a battery?

[diets]

microsash is using a lithium polymer cell - 140 mAh as far as i know.

The truck has one major problem - the articulation has an enormous influence on the steering. You can only solve this problem, if the servo is mounted/connected to the axle. As it is done on the larger (1/10) crawlers.

He has modified his concept and is now using a seperate servo for each axle.



Here is the coresponding thread http://549.rapidforum.com/topic=102177466221

But this increases the overall length/size It isn't a zipzap any more

diets - the smaller the servos, the smaller the truck

[Steve]

finally took it out for a little video shoot...





Video (400k WMV)

[frizzen]

Nice vid! Turning radius looks wicked!!!

Noticed it got high centered a couple times. While you were modding, did you do long travel suspension on it? Softer springs and wheel weights would help too.

How about some closeups of the body?

[Steve]

This is the truck that just plain has issues. The fact that there is even a body on it right now is a mystery. It has as much suspension throw as it's gonna get, but with the stock springs, it doesn't even move anyway, so until I find softer ones... also, the drive gear, since it's been moved to the middle of the chasis, it has nothing to keep it off the ground, and because it hangs so low, its destined to get caught up on things.

Also, seriously under powered. It runs on three cells, but it's just not geared low enough to matter, and because the motor is under the PCB, raising it even a little to get some more gears in there is gonna be tough.

The body (dubbed Caged Fury) was lengthened about 1/8 of an inch to accomodate the batteries that now sit where the steering motor is (front and back). I'll get some pics once I get the batteries for the still camera.

I haven't given up on it completely, I'd still like to see articulation and lower gearing, just not sure if I can do it in such a small package. I'm thinking it needs to be built from the ground up with those ideas in mind.

[Steve]

Reworked the drive train using a worm gear, and added articulation. Motor and gears are contained entirely within the chassis, which remains stock in length. I have no idea about the gear ratio of a worm gear, so it's pretty much anyones guess if it will go. The articulation AND 4ws combined creates some interesting problems.

in pieces. The rear axel (not pictured) had to be custom made by pulling the hub off, turning the grear around and moving it to the other side. It sounds weird, but it's the only way to get the wheels spinning in the right direction with one drive shaft.




motor will go someplace above worm gear




top view




bottom view. The white mess on the rear end is where the bearings are for the drive shaft. The chassis was built up around those bearings, needed to be strong because it's the only thing holding the rear end on.




4ws



articulation

[GerG]

Nice work. How does it perform?

[Michael.mt2k]

Really nice work!

Man, the mods I'm seeing done to these ZZ MTs are awesome!

[frizzen]

That's looking a LOT better, should be much more Trail worthy than just Stadium worthy like your Mk.1 version!

Did you move the driveshaft to the chassis centerline? Where are you planning on hiding the batteries? (rear end?)

I like the rollbar on the Ram! Scratchbuild or hotwheels donor?

[Steve]

Originally posted by frizzen
That's looking a LOT better, should be much more Trail worthy than just Stadium worthy like your Mk.1 version!

Did you move the driveshaft to the chassis centerline? Where are you planning on hiding the batteries? (rear end?)

I like the rollbar on the Ram! Scratchbuild or hotwheels donor?

The drive shaft remains in the stock position, slightly offset. That is why simply turning the axel around for the articulated end wouldn't work. It would be great if you could just slide that bevel gear over a bit, but the axel itself has a stop on it. So I moved the gear to the other side and crammed it over as far as I could. The batteries sit almost on top of the worm gear. They raise the PCB up only slightly, not enough to cause any real problems.

What it lacks now (still) is power I think. Having two upgraded steering motors, and the added strain of all 4 wheels trying to turn at different speeds when cornering, plus the excessively in-efficient worm gear conflaguration, is brutal on battery life.

The body was just for size comparison, but I think the roll-bar was in fact a hotwheels trans-plant.