Phoxtane Posted January 13, 2014 Posted January 13, 2014 The thought came to me today as I was pulling away from a stop sign and my tires were spinning on ice... if a limited-slip differential is desirable in some situations, and a standard differential is useful in others, why not combine the functionality of the two? Is it even feasible, or even useful? Quote
andythenorth Posted January 13, 2014 Posted January 13, 2014 Diff-locks? Sariel has a design for diff-locks using a small pneumatic cylinder. Works well. http://sariel.pl/2012/05/compact-axle-with-a-differential-lock/ The link above locks a standard diff, not limited-slip. A diff that is lockable *and* limited-slip might be quite complicated Quote
whale2 Posted January 13, 2014 Posted January 13, 2014 There are some real life examples of this. Many off-road cars have lockable differential. Early Audi Quattros have it. Fully lockable, not limited slip. Many modern cars have electronically controlled differential. It works by pulse-braking slipping wheel by applying pressure to it's brake mechanism. Quote
Johnny P Posted January 13, 2014 Posted January 13, 2014 I have a suzuki samurai for offroading. The rear axle has permantly locked diff. The front axle has a automatic one. When the front axle gets power from the drive axle it locks. When you disengage the power to the frontaxle it opens.this is purely mechanical ,nothing electrical about it. I just put my gearbox in 4x4 or 2x4 and it engages or disengages. don't know How the internals work. But it is a EZ locker. Quote
Dans lego Posted January 13, 2014 Posted January 13, 2014 (edited) Hello , I have made a realistic 4x4 chassis with lockable front and rear diffs but not limeted slip, although 88high has a video of a limeted slip diff on his youtube account hope this helps - Dan Edited January 13, 2014 by Dans lego Quote
Rockbrick Posted January 13, 2014 Posted January 13, 2014 That video does not show a limited slip diff its a locked diff with some free play Quote
SNIPE Posted January 13, 2014 Posted January 13, 2014 (edited) Can't you just use a 1 or 2 24 tooth clutch gear connected to a crown gear which is driven by a motor or is the clutch to strong? I'm not sure what on demand means here. Edited January 13, 2014 by SNIPE Quote
Thirdwigg Posted January 13, 2014 Posted January 13, 2014 I have found a 24 clutch next to a differential works best. See here. Quote
Dion Posted January 14, 2014 Posted January 14, 2014 That design look very good. But i think that it will only work when the car isn't to heavy. Quote
SNIPE Posted January 14, 2014 Posted January 14, 2014 Won't the 8 tooth gear get destryed? you can easily seperate the turntable so just put the clutch gear inside of that,, close it back up then you can attach the wheel to the turn table mount holes for the black half of the turntable and still use the clutch by putting the axle through it tat goes to the wheel too.you may need to desighn some hub so it can connect to the turntable and the clutch gear, the grey part of the turntable Does Not rotate, it goes to the chassis directly :) Quote
nicjasno Posted January 14, 2014 Posted January 14, 2014 Add another friction clutch. I think this system is pure genius. Quote
Boxerlego Posted January 14, 2014 Posted January 14, 2014 (edited) I had a car that used break drums for the back wheels and when a bunch of break dust would gather inside them they would slip every time I touched the break. Edited January 14, 2014 by Boxerlego Quote
Hrafn Posted January 14, 2014 Posted January 14, 2014 Won't the 8 tooth gear get destryed? you can easily seperate the turntable so just put the clutch gear inside of that,, close it back up then you can attach the wheel to the turn table mount holes for the black half of the turntable and still use the clutch by putting the axle through it tat goes to the wheel too.you may need to desighn some hub so it can connect to the turntable and the clutch gear, the grey part of the turntable Does Not rotate, it goes to the chassis directly :) But then he'd no longer have a portal axle, if I'm understanding your idea correctly. Quote
SNIPE Posted January 14, 2014 Posted January 14, 2014 (edited) Wouldnt you be better off hooking the clutch gear to the diff from the inside, its easy to unclip the diff so its in two parts. also I would just have a direct drive system instead of putting a gear on top of the differental as I think the gear will get damaged due to the torque but maybe not, im too scared to try and see :P Instead, I have used a high torque NXT 3 motor in either example, you dont have to add the transparent half of the turntable in the first example with one motor. but the other half of the turntable can just connect to the chassis and doesnt need to rotate for this. The second example should be exxelant for off roading. the motor spins the clutch which spins the turntable however if the wheel gets stuck or whatever the clutch inside of the gear will start to work, you can either attach the wheel to the clutch or to the turntable or both depending on how much strengh you want. You can use other motors if you need more speed but I think torque is more important in lego as the speed is fairly limited. Edited January 14, 2014 by SNIPE Quote
Hrafn Posted January 14, 2014 Posted January 14, 2014 The second example should be exxelant for off roading. the motor spins the clutch which spins the turntable however if the wheel gets stuck or whatever the clutch inside of the gear will start to work, you can either attach the wheel to the clutch or to the turntable or both depending on how much strengh you want. If you attach the wheel to both the axle (going through the clutch gear) AND the turntable, what's the point of the clutch? In the setup you showed, I don't think you really have a LSD - if the wheels get stuck, the axles going through the clutch gears will just spin fruitlessly, with the torque going to each wheel limited to the slip torque of the clutch gear. That won't happen with Thirdwigg's design - most of the motor's torque will go to at least one wheel in his design no matter what happens, minus the slip torque of the clutch gear which will be transferred to the stuck wheel. If both wheels are stuck, they should both get half the motor's torque. Quote
SNIPE Posted January 14, 2014 Posted January 14, 2014 (edited) The clutch gear is meant to increase torque not slip pointlessly, thats how the clutch drives the wheels, the diff lets them counter rotate, the Tires also help the clutch to stop slipping. Lego is more about trying stuff out and then you can then see what works and what doesnt work, something you cant do in a forum. Im still not sure what on 'demand means', a differential lock? Im not sure how on depand this idea is until it is tried, it may slip too much or not at all, there are a lot of factors involved. I guess you can add gears between the axle for clutch gear and the axle for the motor to give a portal axle., up to 20 tooth wll fit in unless you take the unused half of the turntable away Edited January 14, 2014 by SNIPE Quote
Rockbrick Posted January 14, 2014 Posted January 14, 2014 I think we need to refresh our minds what an LSD really is.... http://en.wikipedia.org/wiki/Limited-slip_differential Quote
aol000xw Posted January 14, 2014 Posted January 14, 2014 I don't see how the clutch works with the diff. When cornering to the side where the clutch gear is, that wheel needs to turn slower, but that wheel can never turn slower unless the vehicle is very very heavy. It works like a locked diff until the diference of forces on each wheel -like when one wheel loses grip- is high enougth to make the clutch slip, then the Diff works as usual, so the vehicle gets stuck. What am I missing? Quote
andythenorth Posted January 14, 2014 Posted January 14, 2014 What am I missing? An LSD is a device to ensure that a wheel with traction does not have torque 'stolen' by a wheel which is spinning. I can't see how adding clutches in the drive train does that. Don't the 24t clutch designs just introduce a loss of torque to the wheel? Quote
SNIPE Posted January 14, 2014 Posted January 14, 2014 (edited) its hard to say how it will behave without trying it, I only have an M motor and one turntable but the clutch feels fairly strong but not super strong, the driving surface also makes a difference. to put it simply: the motor drives the clutch gear from the center which drives the wheel because the clutch is meshed to the turntable inside, if the car is moving and the wheel is becoming hard to rotate then the clutch might help give it some traction. the turntable is connected to the wheel , edit: sorry, you cant have the axle going through the wheel and the clutch, the wheel is attached to the turntable only.on half with the clutch meshed Edited January 14, 2014 by SNIPE Quote
Thirdwigg Posted January 14, 2014 Posted January 14, 2014 Most of my trucks are powered with an XL Motor. Power from an XL, through a clutch, to the wheels does not work If a truck or car gets bogged down. By driving the torque through the differential with the clutch on the side limits slip between the two wheels, and ensures torque will still go to the axle. The clutch is too "soft" to transmit torque on its own. This has been my experience. It worked well on this MOC. Quote
SNIPE Posted January 14, 2014 Posted January 14, 2014 Ah ok, I tried with an M motor a few hours ago, it was terrible, ill try and think of something else :P Quote
clarkdef Posted January 14, 2014 Posted January 14, 2014 What about trailing a few cogs of each side of a stiff axle, the give in the cogs will give you limited slip, no need for a diff, maybe 3 sets of 16 tooth on each side. You probably could get half of rotation independent of each side. sounds pretty lame haha, also doc brown had a good idea using rubber. Quote
SNIPE Posted January 14, 2014 Posted January 14, 2014 Check this out: uses band connected to a arm that adjusts the strength of the band which changes how much slip there is Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.