48P Optima Mid LWB conversion a success.

[alcyon]

Ok after about 2 years of R & D, which included the testing and eventual ruling out of the twin belt system on the Optima Mid, I am glad to announce the success of my 48P conversion. Special thanks to Linus from Sweden who worked with me to suggest gears suitable for this conversion. Currently only available for LWB mid becuase of belt length availability. If i can get a supplier to make a custom length non standard length, then only I can go ahead for SWB.

Parts needed :
1. 3D Printed front gearbox - https://www.shapeways.com/product/XMSJ2VVLH/ot-84-f-1015-sp?optionId=61374621&li=shop-inventory
A new design that houses the re re optima geardiff or ball diff with 10x15 bearings.
2. 3D Printed rear gearbox - https://www.shapeways.com/product/N95ABWES7/ot-84-r-1015-sp-48p?optionId=61539298&li=shop-inventory
A new design, that houses all new gears and re re optima rear diff with 10x15 bearings. You only need the rear upper shock tower which goes in between the slot at the top. The lower upper link tower is not used and a protruding camber mount base is used for placement of a vertical ball stud.
3. HPI top gear. #86945. You need to shim the gear as in the pic shown, and use a re re optima short diff gear pin (2x7mm length).
4. Hot Racing 46T center gear - #SCCR46T.
5. One 4x10x4 bearing, one 4x10x3 bearing, for the hot racing center gear. The 3mm thick bearing must face the spur side gearbox. This is to make sure the center gear goes as close as possible to the inner gearbox surface, you may need to add shims to the original center gear shaft.
6. A new fine tooth modern belt is needed, because you are now using optima Re - re diffs. Belt spec is S3M 660, 220 tooth , 4mm wide.
You can buy the belt from me to 10 bux, or you can buy it yourself. This belt does not skip unlike the old 254XL.
7. A new Idler pulley - https://www.shapeways.com/product/FBY5UBTK7/ot-tw-02
8. Re Re optima Front and rear gear diff or ball diffs. OT-208 x1, OT -221 x1, OT -222 x2
9. 4pcs of 10x15 Diff bearings.



The B4 Layshaft is optional, this conversion can work with both original layshaft and the mid-B4 layshaft.
these pics are taken after 6 packs with 8.5T brushless motor.

[Lonestar]

You need to shim the gear as in the pic shown,

Edit - pics placed now!!!

[alcyon]

Lol lonestar, you were too quick, I was editing my links and placing pics in them.
here are some videos of my tests. 1st 2 vids show test no 3 and 4, last vid test no6.




Ignore my brother he talks too much !

[Delorean]

Amazing work as always Rama

[Lonestar]

Good job on the conversion

That last vid is showing an insaaaaaaanely long straight, even for 8th scale!!! Love the old-school drifting driving style! hope you don't race like this otherwise your competitors will drive inside everytime

nice work!

[alcyon]

Good job on the conversion

That last vid is showing an insaaaaaaanely long straight, even for 8th scale!!! Love the old-school drifting driving style! hope you don't race like this otherwise your competitors will drive inside everytime

nice work!

The track is extremely bumpy thats why the car gets thrown around, I also need to rebuild the shocks. yeah it is all over the place. There will be no races on this track anyway, a old track just re surfaced, so i will concentrate on that track.

[HatTrick]

That's really awesome job!!!

[alcyon]

Todays run, with all 4 rear shocks.

[alcyon]

Screen capture

[rccars4sal]

Nice video. It proves that the good ole opt mid can handle a big track. Looks very fast and smooth.

[Swosh]

That´s an awesome thread. A million thanks for sharing that with us. I have a lwb optima mid too and that's really interesting.

You've changed the belt too. How can you ensure it is brushless proof? Are there any durability / strength indexes?

[Delorean]

That´s an awesome thread. A million thanks for sharing that with us. I have a lwb optima mid too and that's really interesting.

You've changed the belt too. How can you ensure it is brushless proof? Are there any durability / strength indexes?

lol indexes....have you seen him drive the thing? if you're putting more power into a mid than Rama does, then good luck to you!

[Swosh]

The stress on the belt and transmission in General does not come from the motor only but also from the grip on the track.

There are also different kinds of belts, made from different materials (polyurethane, propylene) but of the same size. Maybe some kinds are not tough enough or suitable for other use.

Wouldn't you want to put all chances on your side to prevent the belt from snapping after quite a few packs with a 5.5 brushless on a high bite carpet track? And a snapping belt is not just something I just made up: the tlr 22.4 is reported to experience that occasionally.

Again and for the avoidance of any misunderstanding - at least I hope so - I find the upgrade fantastic. Now if you search on Google for a suitable belt, some further questions will come up.

[Delorean]

Cool man. If you find a better belt, please share with the rest of us

[alcyon]

The stress on the belt and transmission in General does not come from the motor only but also from the grip on the track.

There are also different kinds of belts, made from different materials (polyurethane, propylene) but of the same size. Maybe some kinds are not tough enough or suitable for other use.

Wouldn't you want to put all chances on your side to prevent the belt from snapping after quite a few packs with a 5.5 brushless on a high bite carpet track? And a snapping belt is not just something I just made up: the tlr 22.4 is reported to experience that occasionally.

Again and for the avoidance of any misunderstanding - at least I hope so - I find the upgrade fantastic. Now if you search on Google for a suitable belt, some further questions will come up.

I do not have any of those data and even If i asked this data from the belt supplier , they arent gonna bother giving it to me.
I am just a small time hobbyist working up a solution for first and foremost, myself, and also those who intend to drive their LWB mids for long periods of time.
I do not intend to use 5.5T motors as I have seen X Ray XB4s overheat in 2 min runs in Malaysia. The heat generated by such low turn motors and high ambient temps will kill batteries very quickly. Even with the 8.5T I am seeing 1 year batt life with regular usage.
Also if you read the manual for Re re RC10, the max motor is 8.5T, and I suspect its the same for re re optima. As such I also dont see the need for a 5.5T or anything below a 8.5T.

From my testing of the twin belt system which I extensively tested, which had one short belt driven off from layshaft, which then drives the rear diff, then drives the front diff, I broke 3 short belts. The short belt is under tremendous stress ,as its not just driving the rear diff but also the fronts, and it was clearly too much for it.
Even then, I had no failure of the long belt, which drives the front diff, as it is only taking the burden of driving the front diff (which in turns drives the front wheels).
So its safe to say the long belt is able to take the stress. It is now almost 2 years old and as you can see from the pics, still in good shape. I probably ran about 30 packs through it from the time I tested the twin belt system till today.
I cant say for sure how long everything will last on carpet, as I do not have carpet track here, but Linus from Sweden is running his on carpet in his country, and he hasnt said anything about the belt skipping.
As most of the load is taken by the gears, the load on the belt is only to drive the front wheels.
If you are afraid of the belt failing even with 8.5T , lets see how many more packs i can go with this. I will try to get Linus on this forum so that he can update us with his testing.
Also you need to realize something about the way the belt is looped on the mid. I think you will agree that it isnt a very good design, because the belt has to loop over the motor, because of that the wrap of the belt over the diff pulleys, especially the rear one isn't optimal. Right now with 8.5T i dont feel any belt skip under hard braking, but it did skip with the original belts and pulleys. You could run a 5.5T on the original mid But I am sure when you brake hard, the belt is gonna skip the pulleys.