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I have been working on this for the past 7 months and I seem to finally reach a stage where I can really test this new belt drive. Basically I want to replace the gearset in the gearbox with a short belt.
These has a few major advantages.
1. No need greasing of gears , thus cutting down maintenance time of cleaning the gears.
2. Eliminate slop and increasing backlash on the gears as they wear , and as it develops slop, the wear increases exponentially as the impact on the gears increases. with the tensioned belt drive there will be no slop internally.
3. The whole driveline will be much less sensitive to dirt ingestion, since there is no sticky grease in the gearbox.

Disadvantage
1. Since the belt needs to be tensioned tightly there will be some loss of efficiency.

Ok, I got a machinist to make up a twin belt ball diff for me and 13t top pulley, but the first iteration was a failure, because the belt skipped of the pulleys. I thought only the new fine pitch belt sklipped but in fact it was both the fine pitch and the Mid belt slipped, because the 13T pulley was too small and the profile was cut incorrectly. I later found out the technical reference for the pulley tooth dimensions were wrong causing the belt to not engage completely with the tooth, most of this is caused by the inner bottom radius on the tooth being too large.
To cut a long story short, after a lot of testing I finally got a tooth profile that works for both the original mid belt and the new short belt. I am still not entirely happy with the tooth profile and i intend to improve the profile for a bit more clearance for the production runs.
I decided to make my pulleys with shapeways as they are much quicker and cheaper than my machinist, however i do have some shirnkage issues with the smallest diff outdrive holes on the diff cases.
1. Shown below is the second version of my design, its a LA-1 pulley matched to my own designed Mid XL belt pulley, you can see the slip marks on the Mid pulley becuase the tooth profile is not quite right. I used LA-1 to isolate which side the slipping was coming from.

2. This is the upper pulley which is now 14T, made by 3racing but machined minorly by my brother to enlarge the inner hole from 4mm to 5mm and to make a 2mm slot on the pulley hub, to lock it down like OT86. A 3D printed insert keeps the pin from falling out.

3. The original center gear position cannot be used for the most suitable belt length, so a hole must be drilled( i used a 3D printed jig to dill this new 8mm hole, and i made a offset insert to place the center gear shaft. This insert will be available in many different offsets to cater for tension adjustment.

4. How the single short belt looks like assembled.

5. How it looks like with both belts.

As i said, i had issues with the machined pulley so I revised the dimensions on the pulleys and Got it 3D printed by shapeways.
This are the pulleys i designed, and its compatible with Optima Re re gear diff parts, but internally its same as the Old design gear diffs (no o ring and gasket).


This pic shows the gearbox assembled up.

I tested the car in my house last night with the latest pulleys and finally there is no belt skipping sound, even with tight clutch and the front wheel lifting slightly. I will test the car this saturday and if it works good i will go on with a long term test. Oh yes, the internal ratio is now 2.214..same as Lazer ZX.

Nice mod.

IMO there is one more advantage of twin belt.
Lower the CG by moving motor and lipo into a lower position.

Very cool. Will be interesting to see how well it holds up, and if there is a noticeable difference in speed. Do you think the 3d print pullies will withstand the friction and wear? Im just super curious about all this 3d print stuff.

Lin, there is no change in CG because the original belt is re used and its position is the same. When i design something i always try to re use as much parts as possible.
RCcars4sal, i think top speed will be the same, I really don't think I can feel the difference. Its mostly to make the car more maintenance free in the long run, thus saving your time. As for 3D prints, the ones made by shapeways are by SLS method, and they are very strong. I even made up a bumper and will test it too.
and coming soon, sealed Mid Geardiff ,uses components from Optima Re re gear diff, gaskets and O rings, for this twin belt conversion.




I also made up a few things on my shapeways store, one of them the OT-93 bumper.
http://www.shapeways.com/product/CH2A84CJF/ot-93-with-logo?optionId=60721084

Wow, very nice mod!
I'd definitely get one of these once the kinks are ironed out!

Would a system like this work on a vintage Turbo Optima as well?

HatTrick wrote:Wow, very nice mod!
I'd definitely get one of these once the kinks are ironed out!

Would a system like this work on a vintage Turbo Optima as well?

Well not directly but should be possible. Problem is i dont have an optima to base my design on.These last few months the main problem is the tooth profile. Now it seems correct with no slipping but i want a bit more tooth clearance.

alcyon wrote:

HatTrick wrote:Wow, very nice mod!
I'd definitely get one of these once the kinks are ironed out!

Would a system like this work on a vintage Turbo Optima as well?

Well not directly but should be possible. Problem is i dont have an optima to base my design on.These last few months the main problem is the tooth profile. Now it seems correct with no slipping but i want a bit more tooth clearance.

I'm planning on making one of my recently aquired Turbo Optimas a runner for vintage racing and one of the first things I'll get is a Belt Conversion kit to enhance reliability and lessen maintenance.
Something like your mod would improve reliability even more which would be a big plus.

Would you need an entire Optima car or just the gearbox to work on?
Thinking that I could send it over to you.

HatTrick wrote:

alcyon wrote:

HatTrick wrote:Wow, very nice mod!
I'd definitely get one of these once the kinks are ironed out!

Would a system like this work on a vintage Turbo Optima as well?

Well not directly but should be possible. Problem is i dont have an optima to base my design on.These last few months the main problem is the tooth profile. Now it seems correct with no slipping but i want a bit more tooth clearance.

I'm planning on making one of my recently aquired Turbo Optimas a runner for vintage racing and one of the first things I'll get is a Belt Conversion kit to enhance reliability and lessen maintenance.
Something like your mod would improve reliability even more which would be a big plus.

Would you need an entire Optima car or just the gearbox to work on?
Thinking that I could send it over to you.

Wow, you are that serious? Yes I can accept your help. I only need rear gearbox and all the parts inside it, required to turn the diffs from the spur. In short, layshaft, spur, Counter gear..any tensioning idlers..and rear gearbox. Do you have currently a chain or belt drive? I hear for a belt drive there is an additional small pulley required. One of the ideas is you can keep the long chain to drive the front diff, but with a new short belt drive for the rear. It should work for both chain and belt drive, just requires a change in sprocket halves. Right now my design is compatible with the old design so any of my new diff halves will fit into the chain or belt sprocket on the optima.

The real benefit for optima would be a belt drive conversion for the main reduction. The outer gear drive is very prone to contamination, and worn gears. A belt drive there would really make the car usable if it were able to withstand severe abuse. Of course a belt to drive the rear diff would help too, as the final pinion is a constant wear item in hard use.
A fully belt driven optima would be fantastic!

Ahh. I just studied the gears you were talking about..and i am afraid its impossible to convert to belt both inside and outside. This is because internally the optima only has 2 gears. So one gear turns in the opposite direction of the other..hence impossible with a belt drive. It is also impossible on the outside..unless its s hyperdrive type belt drive.

Too bad! Would have been a cool idea!

Oh well, still interested in a kit once you get everything working for a future Mid!

For The Optima ,I thought about it in more detail and it is possible ! It's possible if both the internal and external gears be converted to belt. You cannot convert either one only. When both are converted, both will move in the same direction, then this will work !

Tested the twin belt mid and no belt slipping or failures at all! Did ruin one esc by soldering for too long, and damaged the rear gearbox from backflipping and landing on the wing mounts many many times, thanks to the lip of the jump that was designed for 1/8 cars. Most important thing was the twin belt system took the abuse of the 8.5T with a tight clutch with no problems. I will be trying very soon with sealed o ring gear diffs and more clearance pulleys before i give the go ahead for others to purchase.
Hat Trick, did you see my previous post? I said i have an idea of how to convert the optima to triple belt drive.

The final ratio should be about 2.53.

Yep, saw your post and would be very interested in that!

Great to hear about your successful test with your Mid!

Great work Rama mate