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ThunderDragonCy

Talk to me about ball diffs

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Bored at the inlaws. Been mucking around with the setup on my dt03. I am still working on it but on loose surfaces where I am enjoying driving and on the green ckmpound schumacher rt1 tyres on the road it is very oversteery. It's fun but would like a little more predictability to the handling. Aside from setup changes I currently have the kit geared diff with think grease in it. Seems to me that the car puts down its power fairly cleanly, and from what I understand from full size cars a locking diff might actually make it more oversteery because both rear wheels spin up together? I have I got this round my neck and actually there is more traction because the ball diff puts the power down more cleanly? What do you think?

I'm not racing, just bashing and enjoying tinkering. However as much as I would like to delude myself otherwise that I am keeping hop ups sensible the ball diff is pretty much the only thing I haven't bought now so my as well go all in?

What have you got people?

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Great timing to ask about ball diffs, I am toying with swapping to ball diffs from gear diffs in my rwd buggy which is supposed to race on dirt. I have both kinds already though, but know nothing about ball diffs...

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Locking the diff (welding it or replacing it with a spool) in a 1:1 will make it understeer, as one wheel needs to turn faster than the other,(inside wheel has a smaller arc distance to travel,hence differential).

Once you spin them up though, you'll oversteer more as both tyres have lost grip.

In 1:1 you get an LSD  (limited slip diff) , which is the same as a ball diff in the rc world. The benefit of a ball diff is you can effectively set it up as tight or as loose as you want, from spool to open diff. (Too loose though and the ball diff will turn, and the wheels won't,which melts the diff)

Out of interest, how thick was the diff oil you used?

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10 minutes ago, Jonathon Gillham said:

I am toying with swapping to ball diffs from gear diffs in my rwd buggy which is supposed to race on dirt.

On a high grip surface, ie carpet, you won't loose traction, so a gear diff is fine. A ball diff on a high grip could effect steering (understeer) as both wheels will be still trying to push you forward, fighting the change of direction.

A gear diff on a loose surface, the inside wheel (Unweighted wheel) spins up and all the forward power is lost as wheelspin. Which is were a ball diff, set up right, will put power to both wheels.

It's all in the set up though, too tight and you'll start to get understeer, then massive oversteer. Too loose and you'll melt the diff.

Personally I'd stick with the gear diff until you get a handle of the car, otherwise it's just something else to worry about.

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I have just built the gear diffs on my K1 I will check the oil used and let you know. But regarding gear vs ball, as said above, gear diff for high grip surfaces and ball diffs for dirt and loose surfaces. 

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Thanks for the info. I'll keep tinkering with setup and tyres to get something a little more predictable but given I am quite taken with drifting around gravel car parks and dirt tracks I will look at getting a ball diff once I have the car a bit more sorted.

How do you adjust the ball diff by the way?

Oh, in answer to the question about grease I don't gave the pot to hand it its sticky grease and it's marked differential grease on tub

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Ball diffs are great for low traction conditions, gear diffs work great for high grip but you will spin out on loose stuff. Most modern ball diffs can be adjusted while in the car using a hex diver. Older diffs you need to remove the diff to adjust it. 

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I would leave the gear diff in there and tune the handling with suspension and tire changes, personally. Those gear diffs are bulletproof and zero maintenance, and you can't say the same about a ball diff.

I have tried turning a DT02 diff (same as yours) into a limited-slip friction style by using am O-ring behind one of the side gears. Jury's still out on how well it works.

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Just now, markbt73 said:

I would leave the gear diff in there and tune the handling with suspension and tire changes, personally. Those gear diffs are bulletproof and zero maintenance, and you can't say the same about a ball diff.

This was my feeling, but didn't know enough about ball diffs. Good to learn though. 

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1 hour ago, TeaMonster said:

This is the oil I put into my K1 4WD gear diff

2DBBB960-37E0-47C5-B59B-DABCD98A7ED7_zps

 

Let me know how you get on.

I'm thinking of 500k for the dt03 speed run, but hoping it will be OK in my k1 too as I'm not planning on spending a fortune.

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I've found that in the loose stuff it helps to dial back the steering rate by 1/4 to 1/3.

To begin with I thought dialing back the throttle would help but I got back to 1/2 throttle rate and was still spinning out. Once I dialed back the steering however I found that I could run with the throttle full up and mostly was able to avoid situations where I was fish tailing out of control and or spinning out completely. 

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1 hour ago, Wooders28 said:

Let me know how you get on.

I'm thinking of 500k for the dt03 speed run, but hoping it will be OK in my k1 too as I'm not planning on spending a fortune.

Will do, I just need time to finish the build. Just got back from holiday so hopefully get a bit of time this week. 👍

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1 hour ago, Munchbox said:

I've found that in the loose stuff it helps to dial back the steering rate by 1/4 to 1/3.

To begin with I thought dialing back the throttle would help but I got back to 1/2 throttle rate and was still spinning out. Once I dialed back the steering however I found that I could run with the throttle full up and mostly was able to avoid situations where I was fish tailing out of control and or spinning out completely. 

I use vintage acoms 27mhz radio gear. Is there any way I can slow down the steering rate with this kit?

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You can get little electronic gizmos that plug in between your servo and receiver, with little adjustment potentiometers on them that let you adjust servo throw, which translates to steering travel.

 

You can also presumably do it by moving the ball connectors up or down your servo saver arm, but I don't know how much space there is to do this as I don't have a DT-03.

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37 minutes ago, TurnipJF said:

You can get little electronic gizmos that plug in between your servo and receiver, with little adjustment potentiometers on them that let you adjust servo throw, which translates to steering travel.

 

You can also presumably do it by moving the ball connectors up or down your servo saver arm, but I don't know how much space there is to do this as I don't have a DT-03.

Steering arms are already on the lowest setting so short of getting a longer servo saver that is out. Any links you can point me at for said potentiometer gizmos?

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Would thicker oil in the gear diffs approximate an lsd or ball diff? In mine they are really easy to swap in and out so not a major to change between ball and gear diff. Not sure what thickness oil is in the gear diffs but they were built for carpet initially.

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1 hour ago, ThunderDragonCy said:

Steering arms are already on the lowest setting so short of getting a longer servo saver that is out. Any links you can point me at for said potentiometer gizmos?

This one looks quite nifty:

http://www.ebay.co.uk/itm/Servo-Travel-Expander-up-to-180-servo-operation-/232292581782?_trksid=p2385738.m2548.l4275

It not only allows you to limit your servo travel down to 20% of normal - it also allows you to increase it up to 200%.

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In a gear diff, the bevel gears don't actually turn until one wheel goes faster than the other. The whole diff unit, from left wheel to right wheel, will turn as one.

Thicker grease/oil makes it harder for the bevel gears to turn so gives a ball diff (lsd) effect, thicker oil = harder to turn.

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39 minutes ago, Jonathon Gillham said:

Would thicker oil in the gear diffs approximate an lsd or ball diff? In mine they are really easy to swap in and out so not a major to change between ball and gear diff. Not sure what thickness oil is in the gear diffs but they were built for carpet initially.

Thicker oil in a sealed gear diff or grease in an unsealed one limits the slip much like tightening a ball diff does. The key difference is in ease of adjustment vs. ease of maintenance.

 

I have thick AW grease in my Mad Bull gear diff to limit the slip. It is pretty much maintenance free, but if I wanted to adjust it by changing the grease, it would be a messy process that would take a while. On the other hand the ball diff in my F103 is dead easy to adjust, but it needs to be checked after every few runs, and benefits from a complete strip, clean and rebuild after a few race meets.

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