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Old 11-24-2009, 12:29 PM
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Default forward reverse gearbox

this may be a stupid idea, but would it be possible to make a forward/ reverse gearbox, like the comet one? would i be able to incorperate maybe 2 gears as well?
maybe something like this?
http://images.google.co.uk/imgres?im...a%3DN%26um%3D1
also how do they work?
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Old 11-24-2009, 01:36 PM
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Looks like when you switch between reverse and forward, it just either locks or unlocks those 3 small gears from freewheeling. Pretty simple, but making one might be tricky, unless you have access to a milling machine.
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Old 11-24-2009, 01:56 PM
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i have access to a mill and a lathe at school. thanks. i kinda get it now. when the 3 mini gears lock up with the inner gear it is in forward, and the outer gear, reverse. but how does it mesh with the outer gear without moving too far away from the middle drive gear, and not engage? if that makes any sense!
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Old 11-24-2009, 03:13 PM
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No, the gears are always meshed, but when the litte gears freewheel, it reverses the motion. Its kinda hard to explain so i drew it out. Hope it helps.
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Old 11-24-2009, 06:09 PM
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A planetary setup is WAY too complicated, especially for a manual machine. Just look inside a mower trans sometime and see how it does forward/reverse. 2 gears, 2 sprockets, 1 chain, 2 shafts, 4-8 movable keys.
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Old 11-24-2009, 08:54 PM
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i have seen a few of gearboxes like this on equipment
it just shifts between the right and left gear for forward and reverse
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Old 11-25-2009, 12:50 PM
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i think i may make something like above. here is a pic of what my design is. would there be any way of encorperating a reverse gear ratio of like 2.5:1, so i dont do 30mph in reverse?
and btw there will be a lever connected to the shaft with the forward/ reverse gears on.
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Old 11-25-2009, 01:25 PM
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I've got a 8.75" Chrysler rear differential. It has the 4 spider gears you need. You'll probably have to reduce the reverse gear outside the box. These spider gears are pretty hard to find outside of one of their primary uses: Differentials.

The differential I have is HEAVY. 20lbs. I doubt that you'll need the case its in right now. The gears should be all you need. You can make a far lighter case than the one its in now, similar to that in your drawing.
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Old 11-25-2009, 01:39 PM
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so i could probably go to the scrap yard, and rip a diff of a scrap car, and use the gears in that. thx. this is only a possible build tho, and my dad says i should stop adjusting and use my kart! i suppose thats tru tho.
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Old 11-25-2009, 01:45 PM
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any one any idea how much a diff would be?
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Old 11-25-2009, 02:20 PM
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I paid $30 for mine on ebay shipped, and I paid $20 for shipping. I don't particularly need it. They do vary in price. You most definitely want a used "open" (NON limited slip, and not welded like lots of people do to 240sx's for drifting) differential. You should be able to get one for less than $50.

The gears are actually rather expensive new, and are either in good working condition, or completely broken and unusable. There's not a lot of middle ground here.

It's also very hard to find parts for these that aren't make and model specific. I might just be looking in the wrong places, but I would prefer looking through a list with numbers on it reflecting the tooth count, size, etc. Rather than just tell me the model(s) of vehicle that this came stock on.

I don't consider 20lbs to be "heavy", but when I first saw this thing, I knew it was way too heavy for me to be using with a go kart, which is mostly due to how thick the casing is. Go for cheap, small, and light. Trust me, anything that can handle even the lightest of duty in an automobile will hold up very good to whatever you wanna throw at it.
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Old 11-25-2009, 02:33 PM
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http://media.photobucket.com/image/d...e/DSC01261.jpg
these are the gears i need.
i may rip a diff from a car at the scrappy. i am in the uk.
that 20lb includes a lot though. i only need the middle gears, and not the casting, and other gears. the gears i want probably only weigh 5-10lb.
one question. do you know what size i.d the gears are, and if they are splined, keyed ect.
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Old 11-25-2009, 03:17 PM
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You're right. most of the weight is the carrier. (The case that holds the gears and the ring gear bolts to.)

Here's some pics I just took with my phone. Couldn't find a better camera.

http://img515.imageshack.us/g/dif1.jpg/

This is a pretty heavy-duty differential, though.

The second pic shows the inside of the differential.That's the ring gear with the grooves in it. The diameter is about 1.25" (1 1/4)

The gears, at their widest point, have a diameter of about the size of a CD.
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Old 11-25-2009, 03:46 PM
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thanks.
i have just realised a massive design fault tho with my design, it is always in reverse, and not forward/reverse! lol. any other ideas, or adjustments?
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Old 11-25-2009, 04:01 PM
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Also, this will require you to mount your engine sideways as the drive gear will be perpendicular to the output gear.

If you use the spider gears from the differentials, refer to this: (slightly different pic than above)


The gears are labeled with RED, and the axles are labeled with YELLOW.

Each gear can turn independent of each other as it currently is.

You must remove gear 3 for this to work, and tie gear 2 and 4 together so that they always move in the same direction (and not independent of each other). there's a few ways of doing this.

I suggest lengthening (or getting a longer) axle 1 as per your design so that either gear 2 or gear 4 will be in contact with gear 1, but at no time will both of them try to contact gear 1. Add just a little margin where neither gear will be in contact. Maybe a quarter inch.

Apply power to the sprocket that will be added to gear 1, set up a way of moving the gear2, gear4, and axle1 (which should be made into essentially one part), and keeping them in two specific spots (forward/reverse) and on the outside, put your output sprocket that will move with axle1/gear2/gear4

It'll be tricky, but I like the idea of converting this differential I have into a gearbox. I might try this as well. I'll draw some things up in Inventor later and I'll post it.
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Old 11-26-2009, 02:28 PM
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i think i get it, but then wouldnt the power output be at 90o from the input?
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Old 11-26-2009, 07:14 PM
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Quote:
Originally Posted by r_chez_08 View Post
i think i get it, but then wouldnt the power output be at 90o from the input?
yeah (perpendicular).
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Old 11-27-2009, 01:01 PM
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could you then have a big worm gear and a cog to get it back straight?
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Old 11-27-2009, 06:31 PM
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You could always just go lawnmower style, with 2 parallel shafts, connected together by 2 gears(reverse) or 2 sprockets and a chain(forward) one shaft has the gear and sprocket keyed on, the other uses sliding keys to select between engaging the sprocket or the gear, you can have neutral in between.
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Old 11-27-2009, 08:26 PM
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Quote:
Originally Posted by r_chez_08 View Post
could you then have a big worm gear and a cog to get it back straight?
Such a gear setup typically has a pretty drastic reduction. A Ring and pinion gear would do this, but would reduce your RPMs by a factor of about 7-9 according to the gear setup you chose. This would affect your gearing very drastically for the chain. I'm pretty sure that the ring and pinion setup is the wrong way to go.

But, you only used 3 of your 4 gears. If you can find another spider gear that matches the one you didn't use, you can use that for another perpendicular 1:1 ratio (we want to keep the forward final ratio to 1:1, so that it doesn't affect your chain gearing)
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