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Old 09-24-2017, 01:00 PM   #1711
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How are you guys installing the weights?
I'm thinking press fit in the shoes, and Loctite 603 in the flywheel.
Here's how I installed them in a 2-speed clutch:



Press-fitting the weights into an aluminum flywheel should hold them securely too. Consider that the shoe pivot pins are also press-fit, and they're plenty secure.
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Old 09-24-2017, 01:04 PM   #1712
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that theory is fine and works on most stuff, however it doesnt always work. ive explained before about mechanically regraded gears where they essentially change the shape of the teeth to allow more or less teeth on the same diameter gear. this is very common in 5th scale applications such as fg and mcd and others that use a fixed mount between the engine and layshaft. there also seems to be no standard 1m pitch in r/c, ive been mixing gears from different cars and brands for my custom 2 speed and nothing lines up.
I use Losi-compatible steel pinion gears from RC-Monster, and HPI spur gears, on my RS4s. I much prefer the properly-cut tooth profiles on RC-Monster's gears vs. the ones HPI uses that have wider or narrower teeth to fit different numbers of teeth into the same circumference. Also they're hardened steel instead of aluminum, which will obviously last a lot longer.
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Old 09-24-2017, 01:47 PM   #1713
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ill be checking out the rc-monster stuff when i redesign my 2 speed this winter. right now im having plenty of fun with a single speed and center diff. its not quite as fast but is corners so tight and fast.

i think i need to see if i can build a 2 speed center diff
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Old 09-24-2017, 02:44 PM   #1714
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ill be checking out the rc-monster stuff when i redesign my 2 speed this winter. right now im having plenty of fun with a single speed and center diff. its not quite as fast but is corners so tight and fast.

i think i need to see if i can build a 2 speed center diff
Sharkey, man, you are overdue for a new video. Haha
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Old 09-24-2017, 03:21 PM   #1715
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i havent been doing a whole lot of r/c in the past while. been doing some real car stuff, building engine swap wiring harnesses for late model fuel injected engines, and thats pretty mind numbing work. also ive added a major thing to my bucket list so thats been keeping me busy. ive decided im going to set a land speed record in bonneville at some point.
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Old 09-27-2017, 03:47 PM   #1716
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i think i need to see if i can build a 2 speed center diff
Not easily. The best approach would be the one Traxxas uses, where the slipper clutch, 2-speed, and center diff are all separate transmission stages. Otherwise you'd have to find a one-way bearing *and* a centrifugal clutch that could fit around the outer circumference of the center diff. Probably the most practical approach (though not necessarily the prettiest or most streamlined) would be to adapt a Revo 3.3 gearbox to fit your vehicle.

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i havent been doing a whole lot of r/c in the past while. been doing some real car stuff, building engine swap wiring harnesses for late model fuel injected engines, and thats pretty mind numbing work. also ive added a major thing to my bucket list so thats been keeping me busy. ive decided im going to set a land speed record in bonneville at some point.
Really? Haven't all the records been set so high by racers with sponsors that they're basically impossible for normal people to break now?
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Old 09-27-2017, 07:40 PM   #1717
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Not easily. The best approach would be the one Traxxas uses, where the slipper clutch, 2-speed, and center diff are all separate transmission stages. Otherwise you'd have to find a one-way bearing *and* a centrifugal clutch that could fit around the outer circumference of the center diff. Probably the most practical approach (though not necessarily the prettiest or most streamlined) would be to adapt a Revo 3.3 gearbox to fit your vehicle
or i have to build a center diff small enough to fit to one end of the bulkhead, then have the outer housing neck down small enough to run a one way bearing and 2 speed clutch on. nothing would be off the shelf r/c stuff. its something ive randomly thought about a few times, might need to look further into it when i have some time.

the problem with a revo trans is it has a lot of built in gear reduction, making the gearing problem with a 4 stroke worse.

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Really? Haven't all the records been set so high by racers with sponsors that they're basically impossible for normal people to break now?
no they really havent. there are a ton of different classes you can build a car for. at a quick count there are 76 classes for different car configurations, and each of those classes has records for each engine catagory, up to 19 different engine combinations for each class, and thats just for cars and trucks, let alone everything for bikes. some records are as low as 85mph, and some records havent changed in 30+ years. the key is to pick a car class and engine class that isnt extremely popular and build a car to suit.

a friend of mine went to bonneville this year for the first time, it was his dads life long dream to set a record there. they put together a car, not a huge dollar car, but a fairly impressive engine combo, a twin turbo 260 cubic inch small block ford. the engine made 1100hp on the dyno, however traction issues hurt them and with the boost turned down as low as it would go and feathering the throttle they reset the record at 156mph.

im still sorting out what class i want to run, however i have an engine combo ive been wanting to improve on i built years ago. its a gm 60 degree v6 engine, it works in my favor for the engine class, going to be naturally aspirated on race gas. ill be happy to have 300hp at the wheels out of it, and there are a number of records i would have a chance at depending on what sort of car i put it in.
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Old 09-29-2017, 01:00 AM   #1718
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Well yeah, if you're going to custom-machine parts, then pretty much anything is possible. I was thinking about what's possible with OTS parts.
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Old 09-29-2017, 05:30 PM   #1719
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off the shelf stuff, no, although i think using an off the shelf diff from something like a savage (pretty small and fairly strong with the hardened side/spider gears). build an end cap for it that has a hollow shaft for the 2 speed to ride on and the one output from the diff has to pass through it. going to have to go up from a normal 8mm id one way bearing to something closer to 15mm, and im thinking a 2 shoe style 2nd gear clutch.

hmmm, its starting to sound too easy now, maybe i need to somehow add a slipper clutch to it so it can be a 2 speed slipperential
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Old 09-29-2017, 09:51 PM   #1720
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Heh. Honestly I don't think a typical 2-speed transmission that uses a one-way bearing would be strong enough to withstand the amount of torque necessary to diff-out a center diff anyway, at least not unless the center diff is filled with really thin oil. Remember those one-way bearings are limited in the amount of torque they can transfer.
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Old 09-30-2017, 06:31 AM   #1721
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Heh. Honestly I don't think a typical 2-speed transmission that uses a one-way bearing would be strong enough to withstand the amount of torque necessary to diff-out a center diff anyway, at least not unless the center diff is filled with really thin oil. Remember those one-way bearings are limited in the amount of torque they can transfer.
Adding a differential would only lower the torque on the one way bearing. Unless I'm missing something.
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Old 09-30-2017, 11:16 AM   #1722
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ive never had a one way bearing slip in an r/c transmission.
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Old 10-01-2017, 04:22 PM   #1723
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Adding a differential would only lower the torque on the one way bearing. Unless I'm missing something.
This is true. What I'm thinking about is that having a center diff is (in my experience) only a significant benefit in a high-torque application anyway, so installing a center diff might make it seem more practical to add more torque to the vehicle -- until it grenades the 1st-gear OWB.
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Old 10-01-2017, 07:49 PM   #1724
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a center differential has nothing to do with torque output, it helps provide more traction and smoother, tighter cornering.

in full size vehicles, drive a 4x4 pickup on pavement in 4wd and try to turn a corner, it wont turn very sharp and when you try it will bind the drivetrain up, and if you force it through it will cause a tire to slip and hop and bounce. on dirt it wont do this nearly as bad because the tires will slip on the dirt. now try the same thing in an all wheel drive vehicle that has a center diff, like a subaru, mitsubishi, etc. it drives smooth on pavement because the center diff doesnt allow the drivetrain to bind up.

the same thing happens in r/c, you just really dont notice it happening. a center diff makes turning smoother and tighter. this is also why thicker oil in the diffs is good for fast tracks with sweeping corners and you need thinner oil for a tight track. a center diff wont make you want to add more torque, you actually can end up with less forward traction under throttle with high torque because under hard throttle it can unload the front end and the front tires just spin.

again, ive never had a one way bearing in an r/c transmission fail. sure ive had my share fail in pullstarts but never a transmission. if i do build this 2 speed differential it wont be using a normal 8x12x10mm one way bearing typically found in an r/c transmission, itll be something quite a bit larger, im looking at a 14x20x16mm one way bearing used in helis.
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Old 10-02-2017, 01:48 AM   #1725
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I know how a center diff works. I'm saying it's not terribly useful in a RC that doesn't have a lot of torque in the first place -- so if a RC has enough torque to actually benefit from a center diff, it probably also has enough torque to damage the OWB in a 2-speed transmission.

If you plan to use a larger-than-normal OWB though, that's a different story. I'll be interested to see the resulting build.

Also, yes, the effect of a center diff is extremely noticeable even at RC scales. As an anecdote, I briefly removed the center diff from my MERV about a year ago, and it affected the handling so badly I went through all the trouble to remove the MERV's transmission after a single run and reinstall the center diff again right away.

- - -

On a totally different note, there's a sale on eBay right now for a new-in-box Kyosho SuperTen with a new-in-box FS-26S-C engine included. The only problem is it costs $1900.
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