RohanBeckett Posted February 7, 2011 Posted February 7, 2011 Hi all.. working on a MOC.. and having a bit of a 'stuck' moment.. so thought I'd ask in here.. I still consider myself a newbie working in studless.. so sometimes I find it challenging to get the right geometry, and alignments What I'm trying to do, is create a PF controlled front wheel drive car.. it will eventually be a replica of a real car. I'm trying to build it as scale as possible... so using the 62.4 tires, this is as wide as I can go... as you can see, the diff and steering arms are as compact as can be! I'm having issues trying to get a decent steering setup working.. I've tried various combinations of rack/pinion, as well as levers (as show in the photos), but nothing seems to operate smoothly, and reliably Also.. for ease of driving, some sort of return-to centre... So just wondering if anyone has some suggestions to try? I have a fair range of parts.. so open to anything! Ultimately, this front section will have 2 drive shafts, running back to 2 PF M motors, hidden in the back of the car. With lever-style steering parts removed Would prefer to use the technic steering links, as they add a bit of realism to the model... however if it's not possible I'll try other things Rohan. Quote
Zerobricks Posted February 7, 2011 Posted February 7, 2011 I used this in my redneck rollercoaster: Quote
efferman Posted February 7, 2011 Posted February 7, 2011 i think the 7L steering rack and the pushrods could be a good combination for you. i hope this was your question Quote
allanp Posted February 7, 2011 Posted February 7, 2011 (edited) From the looks of your current setup, this should fit right in. You might want to mess about with the gears, or maybe use a linkage, as it is it will go almost, but not precisely back to centre. Edited February 7, 2011 by allanp Quote
RohanBeckett Posted February 7, 2011 Author Posted February 7, 2011 i think the 7L steering rack and the pushrods could be a good combination for you. i hope this was your question hahah.. typical... the *ONE* part I don't actually own! yes.. I had looked up this part.. for some reason I thought it wouldn't be suitable.. obvious now that the balljoint pins can go on the side! and allanp: and of course, I don't own the hockey spring.... might be time for a bricklink order... now.. what's the odds I can find a seller in australia who has both! ;) thanks for the ideas! it's great to get fired up again, after you get stuck on a problem!! RB Quote
RohanBeckett Posted February 8, 2011 Author Posted February 8, 2011 I had a bit of spare time tonight.. so I tried allanp's idea... works surprisingly well!! Can't quite figure out how... but it's actually returning to centre, without any spring! I think I might move the gears to the front, so there's less axle twisting.. might make it a bit more accurate Once I get the functionality right.. I can work on bracing/strengthening the whole front section And I'm not sure if there's anything I can do, but it slows down considerably, when turning... but that's probably because it's only an M motor driving it... and the steering hits the limits, and causes friction with the CV joint. Will probably put an XL motor in it, and gear it up a bit for a bit of power and speed! wondering if I can run another feed off the drive/diff, to run an engine block.. this particular car has it mounted sideways... so it might be tricky! Thanks again.. I really appreciate everyone's ideas.. I don't have a huge amount of lego time these days.. and I might have been stumped on this for a while... so this has really helped my little moc along! RB Quote
allanp Posted February 8, 2011 Posted February 8, 2011 I hadn't anticipated that it would self centre, but now that I think about it I should have realised that there will be twisting in the axles. This is storing energy so that when you release the power it springs back. Regaurding the slowing down, this could be for a couple of reasons. 1) Those CV hubs have, IMHO, a design flaw. The hub rotates freely in the outer part however, the CV joint is tight inside the hub, this means that the larger the angle of steering, the greater amount of friction you have. I have always found that annoying and I have no idea why they decided to make them so tight. The new female CV joint part (as found in 8070) is fine in this regaurd, runs nice and freely at any angle within it's limits. 2) When the motor is stalled it will draw alot of current. This will sap power from the electronics meaning there will be less power going to the drive motor. 3) You may also be inducing friction by trying to steer the wheels beyond the limit set by the CV joint. You may want to try limiting the amount of steering just a little bit. Hope this helps. Quote
hga09 Posted February 8, 2011 Posted February 8, 2011 And I'm not sure if there's anything I can do, but it slows down considerably, when turning... but that's probably because it's only an M motor driving it... and the steering hits the limits, and causes friction with the CV joint. Will probably put an XL motor in it, and gear it up a bit for a bit of power and speed! PF-M motor draws 850mA when stalled. This could easily drain the available current from the battery box to any other motors in your model. You can test if this is the source of your problem by driving the steering PF-M from a separate battery box. According to the same test, the PF-M motor draws only 310mA under full load (not stalled). Maybe there is a way to include a clutch gear into the steering setup you are using to prevent the M motor from stalling... Quote
RohanBeckett Posted February 11, 2011 Author Posted February 11, 2011 So... I decide to rebuild the whole thing *again*... and make it all a bit stronger... The thin 24t bevel gear was slipping off a bit, so I thought I'd just move the support beam back, and put a double bevel in... should be fine.. as I've seen this setup on other models... Now.. has anyone built a diff and bevel gear exactly like this before? Looks like it'd work fine? Wrong! For some geometric reason.. the double-bevel is a *fraction* too close to the diff... and it grinds... If I pop the supporting beam just out a little, on the friction pins it's mounted on.. it works fine... Compared to this, in 8265: This operates smooth as silk! no grinding at all.. Exact same technic spacing: (not perfectly lined up for the photo, but you get the idea) Turns out the liftarm frame has a TINY bit extra inner-width, end to end... and this is the reason it works fine.. grrrr... rebuilding for a *forth* time now! and I hope it doesn't interfere with the steering rods! I may end up resorting to Zblj's design..... On another note: Comparing the 3 x 3w new Differentials I own.. 2 from 8265, and 1 from 8297... I notice that there's a slight warp/buckle in the outer rim teeth.. Mostly the edges furthermost from the sides of the diff... and it's very slight... however it's noticable when it's spinning... (bit like watching a buckled bike wheel) RB Quote
Blakbird Posted February 11, 2011 Posted February 11, 2011 Now.. has anyone built a diff and bevel gear exactly like this before? Looks like it'd work fine? Wrong! For some geometric reason.. the double-bevel is a *fraction* too close to the diff... and it grinds... If I pop the supporting beam just out a little, on the friction pins it's mounted on.. it works fine... This is not completely surprising. Every LEGO brick, including liftarms, is about 0.1mm smaller than the nominal size of a stud width. This is necessary to get parts to fit next to each other with a slight tolerance and not bind. In your design, you stacked up to 4 1/2 thickness liftarms to space out your gear from the differential, and in the case of LEGO math (4 * 1/2) < 2. So the gear is a little bit closer than if you had used a pair of full width liftarms, and even that would be a little closer than the frame because the frame contains even another 0.1mm compared to two liftarms to account for the space between them. Incidentally, you can validate this by measuring the cross section of a liftarm. You will see that it is NOT quite square. You can also measure the difference between the width and the space between axle holes. Quote
RohanBeckett Posted February 16, 2011 Author Posted February 16, 2011 This is not completely surprising. Every LEGO brick, including liftarms, is about 0.1mm smaller than the nominal size of a stud width. This is necessary to get parts to fit next to each other with a slight tolerance and not bind. In your design, you stacked up to 4 1/2 thickness liftarms to space out your gear from the differential, and in the case of LEGO math (4 * 1/2) < 2. sigh.. yes... it's blatently obvious... when I think about it! anyway.. I've used the frame now, and it all drives smoothly. Now working on the body of the car... despite the subframe being studless, I'm going studded for the body... once I get the dimensions worked out, I can figure out where to hide the motors and battery box and of course.. I have plenty of parts to build it in yellow.... but the *one* part I need several of... Lego has never made in plain yellow! grrrr! Looks like a few bricklink orders, and I'll have to build a red car now! RB Quote
RohanBeckett Posted March 10, 2011 Author Posted March 10, 2011 Well.. I've made some progress! Still not 100% happy with the steering.. It's just got too much slack in it.. and even after I got a Hockey Spring off Bricklink.. it seemed to add friction/drag to one direction of steering... plus of course, the turning circle is crap.. but that's to be expected with front wheel drive. I might build your idea, Zblj, and see if it'll fit into my body work. anyway.. just posting to show a work-in progress: In my original 'hello' post, I showed off a Mini Moke that I'd made as a present for my girlfriend (now wife!) http://www.eurobrick...showtopic=38959 This Easter, we're driving the car 600 km's to a 'Moke Fest'.. probably around 80 vehicles from around Australia meeting up for the long weekend holiday. I'm hoping to have it finished by then, to bring along, and show off! There's some really unusual angles and curves in this little car.. took a bit of experimenting to work out.. a lot of SNOT work too! One day, I might try it in studless.. but for now.. studded is what I build best in! Working Headlights Working Steering wheel Removable Bonnet (same as original car!) PF Remote Controlled Hope to have a mockup engine in here No Suspension, but it's true to the original car - front wheel drive. I think I've improved on the original version! The Real Thing: Quote
S.I Posted March 10, 2011 Posted March 10, 2011 (edited) On another note: Comparing the 3 x 3w new Differentials I own.. 2 from 8265, and 1 from 8297... I notice that there's a slight warp/buckle in the outer rim teeth.. Mostly the edges furthermost from the sides of the diff... and it's very slight... however it's noticable when it's spinning... (bit like watching a buckled bike wheel) RB The differential in my new supercar also is warped :( Edited March 10, 2011 by S.I Quote
DLuders Posted April 23, 2011 Posted April 23, 2011 (edited) RohanBeckett posted this of his completed Mini Moke II: Edited April 23, 2011 by DLuders Quote
RohanBeckett Posted April 23, 2011 Author Posted April 23, 2011 (edited) Haha! beat me to it! :) My family were originally going to drive 550km's to a 'Mokefest' on this weekend, in Central NSW, Australia... but our real Moke has had more unexpected issues, (electrical, and gearbox shifter) and we couldn't rely on it surviving the trip... We went in 2009, and almost 100 cars turned up... they are expecting 70+ this weekend too I'd spent the last 2-3 months building the Lego one, in anticipation of bringing it along, and showing it off (and maybe scoring a few commission-builds! haha - plenty of enthusiasts there who might want their own Lego Moke!) I've mostly finished it, and I took a few photos/videos, and uploaded them, hoping that a few Moke-friends with wifi up there would be able to show them off to others. Working Front Wheel Drive Working Steering Working Headlights (Gear Lever is the light switch!) As close to scale as I could get! - thanks to Sariel's scaler web-app! Mock up engine Various little details like bonnet clips, wipers, rear view mirrors, dash, and passenger handle I still have a bit of work to do with the back.. I'd like to try and conceal the battery box + motors a bit lower, maybe underneath some rear seats. Compared to other car MOC's the others' make.. it was a bit of a challenge building this - as the Moke in real life has no Chassis - the body *is* the bulk of the frame. and there's no cabin, or boot/trunk to hide PF gear in!! :) I also wanted it to be a true front wheel drive too. I spent a bit of time trying to link the steering wheel in, but both gears and U-joints added too much slack, and since the front wheels have limited steering range, due to the FWD, the steering wheel barely moved at all. Still not 100% happy with the steering/driving speed, but it's definitely limited using those Lego Parts - they are really designed for push-along cars, and have too much friction for motor-driven vehicles. And for another challenge, I tried building the smallest Lego Moke I could: More Pics here: https://picasaweb.go...kett/LegoMokeII OK.. now... to find something else unique to build! :-) Rohan. Edited April 23, 2011 by RohanBeckett Quote
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