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Model Forum / Radio Controlled / Land Models / December 2005My Savage
Ok, so last night I pulled the gearbox out of my Savage again to adjust the shiftpoints (1st and 3rd engage too late still). Turned both screws out 90deg. In doing so it got me thinking. How does the box decide to which gear to use? I understand how a 2 speed works, but a 3 speed has 3 centrifugal springs in it. I assume that the springs have different spring rates, but if they both shift by using revs, why doesn't 3rd engage when 2nd is supposed to? If you set 3rd gear tighter than 2nd, it would take more revs to engage 3rd correct? if thats the case, 2nd would have to be set slightly lower and hence the Savage would change into 2nd at lower revs than it would change into 3rd. Or have I got all this screwed up?? On another topic, last time I drove it, I put another slash into my front tire about 10mm from the first one, fingers crossed they dont meet cause then I have a bloody big hole in it! Cheers Dre Inline.............. > Ok, so last night I pulled the gearbox out of my Savage again to adjust > the > shiftpoints (1st and 3rd engage too late still). Turned both screws out > 90deg. In doing so it got me thinking. The ol' 3-speed is a biyatch to tune huh? Took me what seemed like a million dissassemblies to get it right and is the ONLY reason I haven't thrown 40's on it. Bigger tires = different final drive ratio = transmission retune. > How does the box decide to which gear to use? I understand how a 2 speed > works, but a 3 speed has 3 centrifugal springs in it. No, it only has 2 centrifugal clutches. One for 2nd and one for 3rd. 1st is always engaged. On the two speed, you have ONE centrifugal clutch for 2nd gear. >I assume that the > springs have different spring rates, but if they both shift by using revs, [quoted text clipped - 5 lines] > into 2nd at lower revs than it would change into 3rd. Or have I got all > this screwed up?? The box "decides" which gear to use based on the speed at which the transmission shaft is spinning. It has nothing to do with engine revs but actual driveline speed. Remember the engine clutch and slipper clutch is there in the mix so the speed of the transmission shaft is determined by how fast the wheels are spinning. All three tranny "pinion" gears and all three tranny "spur" gears are continually moving. The vehicle is always in 1st gear when the driveline isn't moving. When driveline reaches the speed at which 2nd gear clutch engages, 2nd becomes the driven gear by becoming "locked" to the transmission shaft. 2nd and 3rd are always moving, but they freewheel on the transmission shaft until the clutch engages and makes them the driven gear. Think of it this way, the truck doesn't shift INTO first gear, it shifts OUT of 2nd gear when decellerating. You have overly complicated things. 2nd and 3rd clutches are completely independent of one another. An adjustment on one doesn't affect the other. If you set 3rd tighter it merely makes the truck shift into 3rd at higher speed; no adjustment to 2nd is necessary. Now, if you set 3rd too loose and 2nd too tight, the truck will shift from 1st to 3rd and completely miss 2nd gear. 90* is a lot of travel when you have the shift points pretty close to where you want them. Sometimes 22.5* or 45* is all they need to get em' just right. Think of it this way, 1st gear is always engaged. You can only control when it shifts into 2nd and 3rd. The screw you can get at with the tranny assembled determines when it shifts into 3rd. The hidden screw determines when it shifts into 2nd. > On another topic, last time I drove it, I put another slash into my front > tire about 10mm from the first one, fingers crossed they dont meet cause > then I have a bloody big hole in it! > > Cheers Dre At least you're driving yours! Mine won't run worth a bunk in the cold weather. The Mayhem on the other hand is a snow-spewing nitro blast! Doc > Inline.............. > [quoted text clipped - 67 lines] > > Doc Dude that was quite possibly the most informative reply in the history of Usenet :-D! FWIW - My truck keeps melting spurs, I have no explanation for this. So instead of solving the problem, I'm going to think around it, and just bung metal CB and Spur on - then see what happens...  SignatureDan >> Inline.............. >> [quoted text clipped - 77 lines] > instead of solving the problem, I'm going to think around it, and just > bung metal CB and Spur on - then see what happens... <graciously bows at compliment> With the spurs, I bet the CB/spur pitch is different between the two and incompatible. What CB and what Spur? Check here to see if they're cool with one another: http://www.hpiracing.com/graphics/instr/savagegears.jpg Either that or you don't have the gear mesh right (too loose). Doc > With the spurs, I bet the CB/spur pitch is different between the two and > incompatible. What CB and what Spur? Check here to see if they're cool > with one another: > > http://www.hpiracing.com/graphics/instr/savagegears.jpg 49/17 - Pukka HPi Spur and CB > Either that or you don't have the gear mesh right (too loose). Nah i've been at this game for ages and never had a problem before. Plus, they're not shreading, they're actually melting. But, i discovered the idle was too high and the brakes were binding, so at a standstill the clutch was probably engaging, massive heat build up, melted spur (all the teeth, the front, everything, total mess), I used to run a vented 15t CB but obviously, K4.6 and 15/49 gearing is a bit front end lifty :) Sorted the carb and brake setup now so we'll give this a whirl and see what happens.... > Doc > > Inline.............. > > [quoted text clipped - 74 lines] > instead of solving the problem, I'm going to think around it, and just bung > metal CB and Spur on - then see what happens... The only thing I can think of is incorrect (too loose or too tight) gear mesh. But stuff it, get a RR one and never look back :) Do you use the paper trick to set the gear mesh? (I dont personally, but then I have no probs doing it visually) IMO you want to be able to spin the gears with your fingers and they should keep spinning for a little while after, if they stop straight away, too tight... Cheers Dre > "DanTXD" <me@privacy.net> wrote in message > The only thing I can think of is incorrect (too loose or too tight) gear [quoted text clipped - 7 lines] > keep spinning for a little while after, if they stop straight away, too > tight... Nah dudes you're both mis-understanding, I wasn't very clear, they're not shreading, they're actually melting, the teeth and the front of the spur! The CB was obviously rubbing on the spur, and if you see my other post re: brakes catching and high idle - I think that was my problem, which i have now sorted, so we'll see I guess... Merry Christmas and Happy New Year to you all! SignatureDan >> "DanTXD" <me@privacy.net> wrote in message >> The only thing I can think of is incorrect (too loose or too tight) gear [quoted text clipped - 15 lines] > > Merry Christmas and Happy New Year to you all! Gotcha! After re-explanation I think you found the problem. Mega heat and plastic meltage as a result of heat, not rubbing or bad gear mesh. Hell, good thing the ol' Mayhem has a titanium spur and CB or the same sh.t would have happened to me last weekend. After playing in the snow I noticed that the CB was "wobbly." When I pulled the CB off both CB bearings had disintegrated and the clutch was so worn the only thing making contact with the CB was the springs! Should be up and running for some drunken New Year's driving! Doc > > "DanTXD" <me@privacy.net> wrote in message > > The only thing I can think of is incorrect (too loose or too tight) gear [quoted text clipped - 15 lines] > > Merry Christmas and Happy New Year to you all! You too mate! I see what you mean now, but a steel RR set will solve ya probs, you know you want one, oh and put a nice purple anodized 5mm nut on the end (like 10th scale on road sedans, bling bling remember :) Cheers Dre > I see what you mean now, but a steel RR set will solve ya probs, you know > you want one, oh and put a nice purple anodized 5mm nut on the end (like > 10th scale on road sedans, bling bling remember :) > > Cheers Dre Oh you and your bling! ;-) Doc > Inline.............. > [quoted text clipped - 7 lines] > thrown 40's on it. Bigger tires = different final drive ratio = > transmission retune. hehehe, totally understand :) > > How does the box decide to which gear to use? I understand how a 2 speed > > works, but a 3 speed has 3 centrifugal springs in it. > > No, it only has 2 centrifugal clutches. One for 2nd and one for 3rd. 1st > is always engaged. On the two speed, you have ONE centrifugal clutch for > 2nd gear. Doh! Thats what I had in my mind, but it didn't come out right.. (my fault for posting too early in the moring :) > >I assume that the > > springs have different spring rates, but if they both shift by using revs, [quoted text clipped - 20 lines] > gear. Think of it this way, the truck doesn't shift INTO first gear, it > shifts OUT of 2nd gear when decellerating. But this is where I get hell confused. The shaft that spans all 4 gears in the middle of the box is the one we are talking about yes? The one with the 2 clutches? Isn't 1st gear sitting on a one way bearing? So therefore, once in 2nd, 1st is freewheeling? If thats the case, 2nd is locked in and the main shaft is now spinning quicker due to 2nd gear ratio. Come in third, 2nd gear freewheels (as does 1st). Is this right? (I think I have it even though I may not have written it correctly) > You have overly complicated things. 2nd and 3rd clutches are completely > independent of one another. An adjustment on one doesn't affect the other. [quoted text clipped - 5 lines] > you want them. Sometimes 22.5* or 45* is all they need to get em' just > right. See thats the thing, I thought I was close, but then I drove it on short grass and I am further off than I thought. This is also the last adjustment I do at 90deg, the manual states to start with 90 and then drop down to 45/22.5 so thats where I go next. Over christmas I'll get a chance to really tune the thing (and I cant bloody wait :) > Think of it this way, 1st gear is always engaged. You can only control when > it shifts into 2nd and 3rd. The screw you can get at with the tranny [quoted text clipped - 11 lines] > > Doc LOL, not very often, but that'll change in the holidays, YAY! Have a bloody good christmas all! Cheers Dre In-in-line................. >> All three tranny "pinion" gears and all three tranny "spur" gears are >> continually moving. The vehicle is always in 1st gear when the driveline [quoted text clipped - 8 lines] > in > the middle of the box is the one we are talking about yes? Yep! >The one with the 2 clutches? Yep again! >Isn't 1st gear sitting on a one way bearing? Can't remember, but I think so. >So therefore,once in 2nd, 1st is freewheeling? If thats the case, 2nd is >locked in and > the main shaft is now spinning quicker due to 2nd gear ratio. Come in > third, 2nd gear freewheels (as does 1st). Is this right? (I think I have > it even though I may not have written it correctly) Yeah you got it for the most part. If you look at the inside of 2nd and 3rd (the side where the clutch is) you'll see little nubs where the clutch pawls grab and engage the gear. When in third, 1st and 2nd are still engaged, but because 3rd overdrives them both they just spin along with third or "freewheel" in a sense. 1st gear = 1st engaged, 2nd clutch disengaged, 3rd clutch disengaged 2nd gear = 1st engaged, 2nd clutch engaged, 3rd clutch disengaged 3rd gear = 1st engaged, 2nd clutch engaged, 3rd clutch engaged > See thats the thing, I thought I was close, but then I drove it on short > grass and I am further off than I thought. This is also the last > adjustment > I do at 90deg, the manual states to start with 90 and then drop down to > 45/22.5 so thats where I go next. Over christmas I'll get a chance to > really tune the thing (and I cant bloody wait :) I feel your pain; I actually took a day off work to tune the farkin' thing! I installed the three speed right after engine break-in and wanted to get the thing dialed-in ASAP as I hadn't even really driven it yet! Merry Christmas to you too bud! Doc > In-in-line................. > [quoted text clipped - 36 lines] > 2nd gear = 1st engaged, 2nd clutch engaged, 3rd clutch disengaged > 3rd gear = 1st engaged, 2nd clutch engaged, 3rd clutch engaged Yep, no worries, I've got it now. I really need to stop thinking outside the square with this sort of stuff, especially in the mornings :) > > See thats the thing, I thought I was close, but then I drove it on short > > grass and I am further off than I thought. This is also the last [quoted text clipped - 10 lines] > > Doc Thanks mate, looking forward to lots of RC talk in the new year :) Cheers Dre > Thanks mate, looking forward to lots of RC talk in the new year :) > > Cheers Dre I should have some airplane crash pictures shortly as the bulding of the BUHOR has begun! Bwahahahahaha! I'm half tempted to put a wee gasser on the nose so it explodes or at least burts into flames when I crash; nitro doesn't explode nearly as well as gasoline does! Doc |
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