RC10Talk - The Net's Largest Vintage R/C Community

Please explain how a 2 speed transmission works.
I see this kit http://www.hpiracing.com/optionparts/opt-oth.htm and it looks like there is a constant mesh between both sets of pinion/spur gears.
I would imagine there is more to it than meets the eye.
Thanks

one of the spur gears is on a one-way bearing so it just freewheels. it uses a clutch to engage the second gear.

How is the clutch operated?
Obviously, it does not freewheel all the time... what makes it freewheel or not?
Need more info.

dammit Heffay I'm only a doctor not an engineer

Haha... at least you're not a teacher, cuz then I'd really be razzin' ya!

i would guess it engages with centrifugle force. once the car reaches a certain speed, the 2nd gear engages. when you slow down, it drops back into 1st.

Ok... that makes more sense than a radio operated clutch or something with a mechanical clutch of some sort.
I would really like to see a video of someones set up or an exploded diagram.
I'm just curious. Sounds really cool for pavement pounders.

yep, it's kind of confusing unless you really have one in hand and watch what happens.

the primary (first) gear is on hub that has a one way bearing for that gear, and then a mount for small clutches, like a minibike or weedwacker might have, or even a gas/nitro truck, the second gear has a clutch bell that encases these clutches.

the one way bearing is mounted on so that the rotation of the motor locks the bearing so the first gear can drive the transmission.

Once a certain rpm is reached, the springs holding the clutch shoes expand enough that they grip the clutch bell, and the second gear now will start to drive the transmission. since the first gear is on a one way bearing, it will begin to spin faster than it would be driving, which provides the same physics as spinning backwards on the hub, and thus, the one way bearing begins to freewheel the first gear. As you slow down, the reverse process occurs. the concept of the gear freewheeling is the tricky part.

there are a few ways to do this, either with a pinion assembly, or spur gear assembly, etc etc, so what you may see may not look exactly like I've described, but the concept still applies.

this is also the same concept used in 4wd front wheel hubs that use a one way bearing, so the wheel drives in forward, but will still freewheel the outside wheel so the car doesn't push. it's also why I believe these 2 speed transmissions won't work with a reverse esc.

I think 2 speed trannys work great for nitro cars but are useless in an electric. You have to se the point where it shifts. in the early part of a pack, it will shift too soon, mid pack is just right and it will never shift towards the end of the pack. Where as a nitro car will have consistent perfomance from the engine though the whole tank of gas.

Here's the HPI 2 speed ...

OK. I'm really getting it now, I think.
I'm imagining a drum brake, slightly different though, where the whole thing rotates. Rather than a brake lever pushing the shoes out, centrifugal force does the work.
Thanks everyone, learn something new everyday. My quota has been met.

shodog wrote:I think 2 speed trannys work great for nitro cars but are useless in an electric. You have to se the point where it shifts. in the early part of a pack, it will shift too soon, mid pack is just right and it will never shift towards the end of the pack. Where as a nitro car will have consistent perfomance from the engine though the whole tank of gas.

i would think with the capacity/efficiency of lipo packs and the efficency of brushless motors, compared to the nicads that were around when the 2 speed came out....... and brushed motors, today..... you should be able to get through a heat race without any issues. i have no first hand experience with them, so i'm just speculating.

good points, shodog and scr8p.
I really didn't even know there was such a thing until I was google-ing the 6 gear tranny just to see what it looked like... then noticed the 2 spurs picture in the link I posted and was really intrigued.

Is there any sort of adjustability to when the centrifugal clutch would engage? I would guess replacing springs of different tensions would work.

Heffay wrote:Is there any sort of adjustability to when the centrifugal clutch would engage? I would guess replacing springs of different tensions would work.

on the HPI unit there is a spring and set screw that you use to adjust the shift point