M18 one-way ball diff

[Lessen]

I'm just curious if this would be possible.

Could you disassemble and reassemble the one-way diff so that the one-way action is backwards? (not just flipping the diff, that wouldnt' work)

 

[Mondo]

One way..

A ball diff and one-way are totally different designs. One ways tend to consist of nothing more than a pair of one-way bearings.
If you reversed the one-way bearings you'd effectively have a RWD car with 4WD braking.
Is that what you're out to achieve?

 

[Lessen]

A ball diff and one-way are totally different designs.

ohhhh, my bad. Didn't realize that. Thanks!

If you reversed the one-way bearings you'd effectively have a RWD car with 4WD braking.
Is that what you're out to achieve?

that's exactly what I want to achieve. So is it physically possible to do that? I don't have one of those diffs, that's why I ask.

 

[Plaidfish]

I don't like the one way diffs.....If you like driving hard and drifting they don't work well for that....the front becomes more lazy and it's like having a rear wheel drive car w/ a lil help from the front......haven't tried it on the M18, but I did on a TC3.......

 

[Mondo]

One way diffs

Plaid,

I agree, in the real world of RC on road racing we run a slightly smaller diameter front tire, about 1.0-1.5mm smaller than the rear tires with a one way front diff.
This causes the front wheels to turn faster, thus disengaging the front wheel drive from the drivetrain, so in essence the front wheels are free wheeling via the one-way diff.
If you go into a bend a little too hot and the rear wheels spin out, the one way then engages and this causes the front wheels to pull the car out of the slide.
This works well in the larger scales like 8th on roads a-la Serpent and Kyoshos
Needless to say this is more suited to longer tracks with sweeping bends where you can carry speed thru the turns.
On a small tight track, where Micros tend to drive, a ball diff or standard gear diff is much more suitable.

Regarding Lessen's question, I don't see why it can't be done. You'll need to source a one-way for the M18, strip it down and reverse the one way bearings.

 

[FastEddy]

Just curious, What are you trying to achieve?

 

[Lessen]

thought about making my M18 RWD but still maintain 4 wheel braking

 

[Plaidfish]

I dunno if you want to do that for a track...especially if it's tight......you'll be making your turning radius alot bigger (I think).....and you won't have the front to pull you out of the spins like mondo was saying happens w/ one way....I just want to do the standard ball diffs in my M18.....I got the chassis already and th enew 300 center mount plate just came friday.....I figured while I have the thing in peices I may as well get the diffs and axles now too.....Mondo I see they use a 1/12 scale front shock on some of them....know where / which ones to get????

 

[FastEddy]

What difs are you going to?
I used the difs from the RC 18T all it took was a little moding of the shims.

 

[Lessen]

I'm probably just thinking ahead of the game cuz I don't even have the car running yet but I have a feeling it will handle too well with a little old stock or even stock modified motor. I'll just have to see what it is like when I get it running. I want it to be hard to control. I know that sounds like the total opposite of what one should want but that's what I'm lookin for.

 

[Plaidfish]

it's already hard to control the stinkin thing....LOL....I can't make mine go straight WOT unless I have foams on carpet.....just use the stock wheels on hard stuff and it WILL be a handful......or just wrap elec tape on teh stock tires....wrap 2 thin strips on the outer edges of each rear wheel and leave the front wheels rubber....it will let teh ass slide all over the place but pull you out of bad spots fairly easy

 

[Lessen]

it's already hard to control the stinkin thing

Is yours a stock motor, stock modified, or big block?

 

[Plaidfish]

I used/use an Orion Baja until my graupner speed 300 comes in.........w/ the stock motor I guess it's fine....also the battery pack makes a HUGE difference...I know it did on the TC3 too but I notice much bigger gains w/ 18th cscale stuff and better batts.....I never tried the reedy pack w/ the stock motor though....

 

[Lessen]

I'm gonna use gp's with a Team Orion stocker. I'm gonna steal the six cells from my rc18t project since I havn't wrapped them yet. I guess I'll just use five although I'm pretty sure you can put a sixth one length-wise between those little battery post things.

 

[Diver6127]

If you reverse the oneway you will essentially be doing more damage than good. For one, the motor will be working against the oneway and cause a drag brake effect. This will over heat your motor make short work of it and essentially ruin it. There is no way to have a RWD car with 4 wheel breaking. You have to either choose to have a diff or oneway; 4wd or 2wd; rear braking or 4 wheel braking.

Mondo is correct when referring to "having a smaller diameter" in the front when a front oneway is applied. But the main reason for a split is to bring the front to rear ratio closer so the rotation is more equal. I don't know the calculations or how a front diameter is determined for 1/8 racing since I don't race 1/8 onroads but for 1/10 touring, the reason for the split is either used or not for the reason stated below.

A 1/10 using a front oneway has an inherrant "over drive" ratio calculated in to it's rotation when wheels are cut (trued) to the same OD (outter diameter). Some racers want a more neutral feel when coming around a corner or sweeper. They want to reduce "push" when an onpower situation is present and over steer when off power.

I use a front oneway with the OD of all four foams equal. It suits my driving style (constantly on power in the turns yet modulated with throttle inputs). I do use minimal brakes (drag brakes) and tend to come in a little bit slower in the turns BUT mid way through the turn, I am on power allowing the front oneway to make full use of it's characteristics. I let the fronts pull the rear through the corner instead of looking for equal transition. The rear of my car will hang out a bit but gets pulled through on power.

This is where the driving style must be changed. There are no front brakes in a oneway. This requires you to set up for the turn a little bit earlier but at the same time, the full independent rotation of the wheels (off power) give the best turn-in. On power it locks both front wheels and pulls it straight. This is required for both smaller and equal diameter tires (front to rear). Dialing in "drag brake" will allow the front and rear to respond equally off power. The drag for the front oneway will be present every time you let off the power and the car works against the oneway bearing.

A standard front oneway requires a different driving style. Off-power the outdrives will rotate forward independantly of each other and front main axle. On-power, both outdrive shafts will roate with the front main axle. This is generally est used with high traction; the car leans towards off power understeer and the track doesn't require braking for corners. It will give maximum off power steering and efficiency. It's best suited for a smooth driving style.

A solid oneway has both outdrive shafts connected by and internal locking axle but they're not connected to front main axle. Off power, both shafts will rotate together but independent of the main axle. On power, they will rotate with the oneway bearings in the front axle. It is best suited for medium to high traction tracks that also, don't require breaking for corners. It gives excellent off power steering.

A full time solid axle (locked) will have the outdrive shafts rotate with the main axle for both on and off pwer situations. It's excellent for low to medium traction and when the car leans towards offpower oversteer and/or the track requires braking for corners (you have full braking abilities). It will give less off-power steering and is best for an aggressive driving style. AKA, fast in/out of corners; Late braking; tight apexes.

 

[Lessen]

thanks for the physics lesson professor. I'm gonna try it anyway and see how long my motor lasts. Thanks for your advice though....

 

[Diver6127]

Do as you wish but it will be the same as driving a RWD 1:1 with the front brakes dragging constantly.

 

[Plaidfish]

LOL...Diver I feel I need a certificate of completion for your class.....seriously good stuff....I suck at on road cars (for now) so I just beat mine to hell....I always thought the one way wasn't for me...but after that info I may give one another try in my TC3 and try to change my driving style.....I brake late and come into turns WAY too hot most of the time....I can break traction and drift it but not good sweping lines that keep speed........

 

[Lessen]

Diver, let me apologize for my attitude this morning. I wasn't really ready for all that info at the time. Sorry.

Anyways, I understand what your saying. you know your stuff for sure. I couldn't think of any downsides when I had the idea. W/O having any on-road experience I think I would not like a one-way either, only having rear braking just doesn't make sense to me. Thanks for all the info, now that I'm awake I can make sense of it

 

[Plaidfish]

Lessen I just went and bought some diff rebuilds from my LHS...they had a one way set in there...I was going to buy it but one of the guys had a nice M18, he also races 1/10 Electric TCs said don't do it....on the M18 when you slam the brakes on it sends the ass sliding all over the place.....there's not enough weight on the car to make it stick well.....and you end up breaking ass real easy w/ no pull on the front.......I just bought 2 sets of diff rebuilds so I can have something to run it w/ for now......