ZZ-M and Axle Stall. Better extreme angle climbing?

frizzen · Post by **frizzen** » Fri Apr 07, 2006 12:33 am

Stupid idea with questionable logistics, this will probably get locked/deleted. Sorry mods, I wanted to talk this out and see if I'm simply full of shit, or if this might work. If it might work, I'm definately not opposed to anybody taking the idea and running with it, I've already got too many half-done projects I haven't talked about. This is random BS, I have no idea if it'll really work, might just ruin your ZZ-M, read at own risk.

On extreme angles, we all know the ZZ-M's like to flip from a combination of CG and torque. The CG moves aft as the nose goes up, the front wheels unweight, and with the rear wheels still pulling for everything they've got, it goes over. So far we've tried everything we can think of to get more weight lower or forward to the nose to keep it from lifting; and all of that slows us down, hurts runtimes, makes pimps cry, and other bad stuff...

Then yesterday I was reading this article about RC Rock Crawling:
http://dodge.off-road.com/dodge/article ... ?id=317039
It mentions the Clod Buster axles which pretty much dominate RC Crawling having both axles completely independent power, gearing, and differential setup. Having those act seperately allows an axle to stall which gives "the advantage is that once the front tires are up on a ledge, they can bite onto the steep obstacle with 100% power and pull the truck up and over with a gentle 50% push from the rear." Which sounds a lot better than the Extreme Flipping Action that the shaft-drive, non-differential trucks (like ZZ-M) have due to equal power to all wheels.

Ok, so I've got a stupid idea, and a shaft-drive truck with rear mounted motor. So pretty obviously the seperate motor/gearing setup is out of the question. Though I think we should be able to get roughly the same performance using direct drive to the front with a clutched rearend.

Ok, so to do that all that really has to be done is modify a rear axle. You'll have to do some micrometer work, get some tubing (maybe bearings if you're really crazy), remove black plastic spacer behind drive gear, probably press off a brass bushing, turn the axle down, bond the bevel gear to tubing, reinstall nylon bushing over tube (shim/bore to fit), have tube extend to under where gear teeth are on drive gear (or plan to bond to a cut black plastic thing), trim to length and reinstall black plastic thing, apply epoxy to it's OD (or tube depending on how you're building) near where drive gear sits, reinstall drive gear, let epoxy cure, cut drive gear somewhere between gear teeth and rim mounting area, cut black plastic thing outboard of epoxy (or just check that it's the right length). Now it's only FWD. Then you just have to make a clutch surface on the drive gear where it was cut apart, and how much friction it takes for the newly installed clutch to leave it's stall-speed will determine at what point the rear wheels begin to reduce power.

Half baked idea, again sorry about posting this without anything actually accomplished. I wanted some input on the concept to see if anybody else thought it might have a chance at making the ZZ-M into an even more extreme offroad vehicle.

HirotoR34 · Post by **HirotoR34** » Fri Apr 07, 2006 10:08 pm

It sounds a little confusing at first, but It could work. I've found extending the wheel base and gear reduction work with some success. My latest crawler project (BTW thanks for the gear reduction advice) has turned out to be my best performing MT mod so far. It will climb things that an unmodded MT could only dream of.

I say run with it, but make sure to post some pics.That might help alleviate some of the confusion.

Clint · Post by **Clint** » Sun Jul 30, 2006 6:32 am

Frizzen, if you dont mind, I might try this. I like your idea here.

crazydave · Post by **crazydave** » Sun Jul 30, 2006 10:00 am

I get what you're saying and it sounds like a good idea to me, but I'm little confused because the article in RC Driver seemed to be saying axle stall is a bad thing, and was talking on how to alleviate it. Now you're saying its good thing, and trying to figure out how to get it in ZZ MTs.

See, that's confusing, huh?

sg219 · Post by **sg219** » Sun Jul 30, 2006 2:57 pm

I like the thought and the objective.

Seems like a tough project to complete, but NOT impossible.

No need to apoligize for thinking outloud. I think of alot of things, but never write them down or post them because they either seem stupid or over-the-top.

You took the inititve.

Who knows, maybe someone can pull it off.

I know if I ever came up with a good electronics idea or something worth doing, I'd talk to, or look to, Ph2t for some pointers and guidence.

But even with his advice, I may not acheive my goals.

Going public with a good thought, can and probably will, prosper into something good!!!

I like the idea.

Needs some tuning and some logistics figured out, but I can see it leading to something positive.

Clint · Post by **Clint** » Sun Jul 30, 2006 7:29 pm

I've got a couple of chewed up servos i can convert to fully reversible esc's, they normally power zzmt sized motors, it's a perfect application.

would easily be able to fit one on each axle.

to convert, just desolder the pot and replace it with a 5k ohm trimmer pot(those tiny blue ones at rat shack). adjust pot for neutral. instant micro esc.

gws pico 4 ch rx
ch 1 servo
ch 2 converted esc on front axle
ch 3 converted esc on rear axle
and maybe a winch on ch 4?

frizzen · Post by **frizzen** » Sun Jul 30, 2006 9:37 pm

Clint, I gave an overview of how I proposed it would work, it's fine by me if you wanna attempt, or take it to a higher level. If it works, it had been too good of an idea to let slip by since I was already buried with project cars in work. Honestly I'd forgotten about this idea.

-
crazydave, if you'd read the whole article, you'd find this little tidbit:

The unique trademark of the Clod axles is the differential mounted transmissions and motors. Rather than two axles connected by a center transmission and drive shafts, the Clod axles housed the electric motor right on the side and slightly behind the diff. The benefits were obvious by keeping the weight close to the ground and center of gravity as low as possible, completely eliminating the need for a big, heavy center mounted transmission.
However, there was a downside to this design….or so we all thought!
By having two electric motors wired independently of each other, one of the motors would likely “stall out” under load. Many Clod purists tried to cure the problem with countless modifications and hours of thought but what we started to realize was that this so called “Axle Stall” was one of the reasons that the Clod based rigs were so effective….and we didn’t even know it! Super steep ledges is where the Clod shines!

Which got me thinking about making a slipper-clutch built into the rear axle, so you could still have the "axle stall" climbing benefit, without the hassle of installing a seperate front and rear drive motor system. Basically, allowing the rear-end to be able to stall out while the front keeps pulling, should let you pull angles steeper than you could do before without the front getting light, nosing over, and tumbling down the hill.

Sure this idea was a little half-baked, fairly over the top, and I know prototyping will be a PITA; but it seemed good enough I didn't want to loose it, thanks for bringing it back up! I went this way with it, so that the only custom piece is the rear axle, and if you decide the mod doesn't work how you wanted you can either swap in another stock axle from one of your donors, or just glue it back solid again.

<edit>

You got me interested in this again, so I started breaking the rear end down to it's components. It should be a little easier to convert than I was originally thinking! (Notice axle-shaft changes diameter at bevel gear?)

It should just be a matter of finding the correct size round tubing, and the right drillbits.
</edit>

Wow, clint's wanting to make it into a 1/64 scale Clod Buster Crawler. Best of luck, you're way more ambitious than I!

crazydave · Post by **crazydave** » Sun Jul 30, 2006 10:25 pm

Ok, I guess I misunderstood that article.

I'll have to reread it, at the time his readings didn't make sense to me, but maybe I'll have a better understanding this time.

Clint · Post by **Clint** » Mon Jul 31, 2006 1:31 pm

oh boy.

Well how much would you pay for this?

it's micro,
reversible,
proportional,
comes with a motor and it's own crawling gear box.

75$? nope..

The hbridge looks fet stackable too.

turn up the volume, you can hear the motor zip thru from slow to full throttle..then i slam it forward/reverse a few times.
http://www.v6power.net/clint/mwhq.net/e ... po-esc.wmv

50$

try again....

25$

Nope....

All from a hs-56HB. about 22$

sg219 · Post by **sg219** » Mon Jul 31, 2006 1:57 pm

Very cool!!

What about steering?

Seperate board?

That one looks pretty damn tiny, plenty of room for another board.

crazydave · Post by **crazydave** » Mon Jul 31, 2006 1:59 pm

That kicks ass. So you just need a micro Rx to hook it to and you're set?

Man Clint you're just full of good ideas.

Clint · Post by **Clint** » Mon Jul 31, 2006 2:49 pm

steering is no problem.

already have a 4ch 72mhz rx..waiting on ch 30 crystal(in da mail)

need another hs56hb. will probably have to order that. my other broken
servo is a jr15. they have to be the same.

For normal driving, i'll need to program the channel slave functions
from my heli radio to keep those two esc's in sync. or mess with some 1:1 aeroplane flap mixing modes.

For climbing the airtronics radio will allow me to control the front and rear
wheels independantly from each stick when not in slave mode.

Namuna · Post by **Namuna** » Mon Jul 31, 2006 3:54 pm

Okay, if I understand that near magical level of shit you just pulled off with the Servo into ESC conversion...It would make it that much easier to convert a ZZMT to full propo, right?

Sorry to jump off-topic here, but Clint's Server converted to ESC has some other very cool implications. So instead of ripping apart a $50 Novak Spy, I could rip apart a $22 servo instead!...AND it would leave that much more space to fit the other parts??

Clint · Post by **Clint** » Mon Jul 31, 2006 8:57 pm

Namuna wrote:Okay, if I understand that near magical level of shit you just pulled off with the Servo into ESC conversion...It would make it that much easier to convert a ZZMT to full propo, right?

Sorry to jump off-topic here, but Clint's Server converted to ESC has some other very cool implications. So instead of ripping apart a $50 Novak Spy, I could rip apart a $22 servo instead!...AND it would leave that much more space to fit the other parts??

Basically. Might want to use a bigger servo than what im using for powering the whole zzmt..But they all are about 20-25$(or free if you
can get your LHS guy to hand over a few broken servos)

Wait till I get this thing powering the wheels. want to make sure I dont blow the fets. Also found a nice small trimmer pot today at radio shack. It should hold neutral well. need to find my multimeter. The stock servo pot
was lazy so im replacing it.

beanoman · Post by **beanoman** » Mon Jul 31, 2006 10:12 pm

Using servo boards as ESC's works great, only little 'problem' is that they arnt as effecient as normal esc's.. but for 'Low Power' or micro stuff, its great cause you can pick up micro servos for less than $10.

As an example of something 'low power' thats using servo esc's, took a pic of my tank.. dosn't have the rx in there, but i believe you can even see one of the pots- i just left them on since space isnt too important in this. High wind 130 motors powered by 4 aa's- so not too much wattage right thar, its been going fine for a month or so.

Couldnt imagine buying 2 Spys for this

or even a very cheap esc would add up. so grabbed some old standard servos, and thar she goes!

http://img.photobucket.com/albums/v318/ ... C04207.jpg

Another use is to control actuators with the servo board, which I did in one of my planes... Cant really think of any micro car/truck that got finished using one of them...

Clint, good luck on the ZZMT, your the dude that can pull that off.