Atomic High Precision Ball Differential

[arch2b]

High Precision Ball Differential
DN-005

[arch2b]

EGR MART (Atomic RC general online distribution shop [in Asia] for those that don't know) has this listed at $30.30. you can expect that to be slightly more expensive when bought from domestic shops. the shop here does carry atomic rc products as well as another online shop.

[arch2b]

as i reported earlier, this is already available for purchase in Atomic RC's main web distributor EGR Mart.

if your a continental u.s. owner, you'll be happy to know AtomicMods also has this in stock and ready to ship.

PLEASE note, Atomic RC and AtomicMods are completely different business's. people often refer to these places using abbreviations which others misunderstand.

[MrNanoTrax]

we'll be stocking these too... i personally want 2 give one a try

[-J-]

Well, I was able to pick up on of these at my local Atomic R/C distributor today. I'm in the middle of a move, so I won't be able to run it for a while, but I definitely tell you it's a lot more robust and as a result, a lot heavier than the Kyosho diff.

[arch2b]

i think a little added weight to the dnano might not be a bad thing. i look forward to hearing your experiences with it.

[fraz]

Haven't run yet but we are running and testing tonight. My 962c is pretty dialed on our track from where I last left the setup so the baseline should be prime for testing.

My first impression out of car is VERY NICE. Usually Kyosho ball diffs I consider to be the gold standard. I love their shim adjuster, etc. but they are simply gritty and spring a bit too tough unless you mess with them a bunch. The Atomic was silky smooth out of the box and the spring is much lighter. To give you an idea of range, you cannot lock down this diff so the spur gear will always turn some. What it looks like is they found a tension range appropriate for the little motors with no torque.

As for weight difference, I didn't bust out my scale but it seems comparable to Kyosho ball diff. The construction appears to be aluminum (pressure plates and adjuster) and titanium (axle and spacers) so it is not as heavy as it looks!!!

One mod I am looking at as I type is Dremeling a small opening in the axle housing to access the adjuster nut. The idea is put a finger on the adjuster nut and turn the wheel to adjust with no tools!!

[fraz]

Ok, I will try and be as succinct as possible without ripping Atomic too hard since they have a history of making great products. Here is all of the testing and investigation I did tonight and ultimately, it was a waste and had to go back to Kyosho ball diff. I really want to use this diff but I need to do some engineering recon still and I will keep y'all posted.

PROBLEMS:
1) No instructions and this is not a plug n' play product.
2) Spur gear is not round!! - no matter how you set mesh, the molding on the spur is not accurate enough to be considered round in this scale.
3) Gear tooth pitch is not right - unless they are providing an Atomic pinion gear set, these never mesh right.
4) WARNING: There are 6 screws. They are of 2 different lengths! The long ones are for using the plastic hubs and the short are for the aluminum.
5) WARNING: Aluminum left hub needs modification! No matter which screws you use, there was a total bind when the screws were tightened even to the lightest amount where they would back off.
6) Shim may be needed. When all is said and done, there is not enough gap between spur and motor mount... it rubs!
7) The tolerance of knurled adjuster is VERY small inside motor mount and the diff backed out and undid itself! Not sure if it was from this, the rubbing spur, or the tight mesh... but the diff was unusable and felt like constant drag brake at best.

FIXES:
2&3) I have a brand new Kyosho ball diff I am going to take apart to see if ID is the same and if the balls fit. If so, this should solve majority of the problems.
5) The problem was the aluminum Kyosho hub was too long on inner step and diff may have been designed to only work with plastic hubs. There was tons of material on left hub so I got some 600 grit sandpaper on the granite countertop and took some material off the hub where it meets the axle/e-clip/bearing. Once I did this the short screws torqued up nicely and no more binding.
7) I may end up with a round roll of emory cloth to take some material out of the motor mount where the diff slides through. As it stands there is like 0.1mm of space and that equates to 0.05mm per side of the knurled adjuster. If you know about plastic molding... no way this can be perfect in these tolerances. This will be the last thing I mess with though.


NOTE: it would be one thing if I was a rookie writing this up, but anybody who knows me in the Mini-Z community (or r/c community in general) knows I am fast and have a good mechanical clue This product needs to get a rev2 before re-releasing and I kind of expect Atomic to make good on the product without sticking me for more money.

[arch2b]

wow, thanks for the insight and review. for the less mechanically challenged folks, this will save them time and money to wait for v2. atomic, like pn has a good record for revisions. i'm sure once they get enough feedback they will do some rework.

does thier website still have a forum? if so i would highly suggest copying your review and posting it there as this is a very new product and obviously very flawed.

[fraz]

Originally Posted by arch2b

atomic, like pn has a good record for revisions. i'm sure once they get enough feedback they will do some rework.

Yeah but I think both of them suck for gouging early adopter customers to pay hard earned $$ to pay for their mistakes. If there is a performance improvement, sure I will be happy to pay. But when there are clear mistakes, they should provide the "fix" parts to customers on a case by case recall basis. Example: PN 94mm LCG motor mount. The part is awesome but hold down screw set up for the upright is a joke and well documented. They fixed it in next rev and expect everybody to pay another $40!!

Originally Posted by arch2b

does thier website still have a forum? if so i would highly suggest copying your review and posting it there as this is a very new product and obviously very flawed.

Neither Atomic nor EGR have forums unfortunately


So I tried the Kyosho spur gear swap last night.

~~The good news is the Kyosho spur gear ID fits on the Atomic ball diff.
~~The bad news is the Atomic spur has bigger balls and holes.
~~Once everything is bolted up in the Atomic diff, there is too much of a gap to make up so the diff rings will meet the tiny diff balls used by Kyosho. My next solution that will likely work fine is to make a spacer to take up the difference. I am thinking of taking one of the Kyosho diff rings and gluing it to the back side of the Atomic diff ring to get the tolerance back "in the zone". I will report back on this as I test or if I resort to some other shimming technique.

I think the unfortunate part and the reason that the Atomic diff is so smooth is because of the bigger balls. Though the diff rings are better chromed material so there may be some adopted benefit. However the lighter spring tension range and adjustabillity may make this project worth it.

[arch2b]

i agree it sucks to have to pay for an updated/fixed part but in 10 years mini-z's have been around and parts made, this is the way it's been. to expect anything else is unrealistic. the ONLY time i've hard parts replaced were due to manufacture defects such as screw taps are missing and or at odd angles, etc.

the risk you assume in being an early adopter of anything is that you are the ginuea pig. what would be nice is if they would offer spare parts for order. PN is doing this for many of their latest stuff. Atomic usually sells spur gears seperately as well. this would at least make getting revised parts cheaper than buying the entire ball diff.

3racing has a forum and i'm sure it's only a matter of time before they get into the game. maybe even gpm but i have not heard anything positive from them in a long time. i've had good experiences with 3racing forum responses.

[patrick38]

hi there

wich one off ball diferential do you people like the most ??
kyosho ore the atomic one ?
hope too hear from you
newbie waiting for his dnano

[Marcro]

I'm glad I read this before splurging. I was going to pick this up along with their disc damper set. Thank you for this review and I hope a V2 comes out soon.

[MrNanoTrax]

kyosho's ball diff is fine... only thing i'd recommend is replacing the stock spacers with thinner washers to allow for more adjustment since the "1" plate setting is worthless

[Jellis]

I thought it was kind of a toss up between the 2 diffs mening they both had there own set of proplems. I'm a machinist by trade so I didn't have any proplem fixing either diff.

The kyosho diff was easy to fix I fully compressed the spring 40 or 50 times to take some of the tension out. Then I found that armature spacers from a slot car motor are an exact replacement for the thick plastic stock shims and they come in various thicknesses .020",.010", .007", .005" for and almost infinate adjustment. If you have a local slot car track (good luck) they should have them in stock.

The Atomic diff had many more problems 1. Adjuster nut and spring hit axel housing, 2. LR drive hub hit axel in center of hub, 3. Gear very loose on hub ( I havn't fixed this yet), 4. Gear seems to be a different pitch than pinion.

1. I fixed the axel housing by reaming it larger I think a drill bit might crack the housing. Also be carefull to make is just smaller than the bearing diameter so the bearing has a lip to set against. I also changed the aluminum nut to a nylon lock nut that I machined round, Drilled a hole in the side of it and made a slot in the axel housing to adjust it without removing the axel.

2. I machined the LR hub back there was alot of material and this didn't hurt anything

3. I havn't fixed the gear on the hub yet

4. I have been running the gear with the stock pinion and other than a little bit of noise I havn't had any problems but may seem a little bound up even with a good gear lash

I did a back to back test of both diffs last weekend 100 laps each taking out the worst 15 laps for my crappy driving.

The atomic diff was first with an average lap time of 4.79 and a fast lap of 4.41

The kyosho diff was a little faster with an average lap time of 4.61 and a fast lap of 4.23

I know some of this was covered in other posts but you know the saying everyone has an opinion and something something .........