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DamonMM2000 posted a topic in LEGO Technic and Model TeamA LEGO® MINDSTORMS® Ev3 2WD/RWD rock crawler inspired trial truck with live axle suspension, 80 N.cm torque thanks to the special adder mechanism, and more. Built for off-road yet also for speed racing 74 feet in 26.49 seconds (2 mph). For the video please click here: PS-Could someone show me how to embed YouTube videos? Thank you!
Hello everyone. New here….been lurking for a little while, and staggered at the amazing creations you’re all making. Inspired by you all and decided to finally go off piste and make something of my own. My first MOC…a tank. I’ve seen many of your tanks, and love the intricate detail and modeling of real world tanks. Maybe one day I’ll get to the same level. This being my first ever MOC, it’s been a huge learning curve, with much trial and error of trying to get things to fit, trying to achieve a decent quality of packaging, trying to be clever (failing mostly lol), and also trying to figure out ways of achieving things, like a firing mechanism and a way to reload the tank. It’s a very large tank with loads of space to add things. I have to admit to making it large because I don’t yet have the skills to make something uber compact lol. I’ve taken photos all the way through, and it’s still a long way from finished. I was concentrating on getting a strong chassis and getting the various mechanisms working satisfactorily. You’ll see as you go through the photos and narrative that I’ve effectively tried 3 chassis frames, initially with studless, then a mixture with studded, and finally making it all studded as there was just too much flex and too many pieces involved with studless. Lesson learned there. The firing mechanism also took some thinking, but I’m pretty happy with it now. As you’ll see I wanted to use 4 Unimog springs for an ultra powerful weapon, but the cams just couldn’t handle it. The mechanism to raise and lower the barrel has gone through two iterations, and I’m now much more pleased that it now goes through the turntable with the motor underneath it and in the chassis. Then there is the steering and drivetrain. Initially I just had a motor on each track to get the thing moving, but wanted more sophistication, so had to go through 5 iterations to get one that finally did what I wanted and had enough torque to turn the tracks and steer it. All the iterations were based on the same principle of adders and subtractors, but the Lego would come apart under the strain, or once the structure was put into the chassis, it just couldn’t turn the tracks etc etc. So now I’m ready to build a body around the chassis and turret and make it look more tank like rather than just a bare bones chassis. I welcome your thoughts, comments, criticisms. Be gentle ;)…it’s my first effort. Anyway, here are the photos from the very start…with some really daft ideas that were soon ditched lol. 1 - Basic chassis. Things are so much harder when there are no instructions. 2 - Torsion bar suspension to allow the road wheels to move over obstacles 3 - Temporary location for power supply for testing. 4 - With the tracks added, it now looks like a tank chassis :-) 5 - Torsion beam suspension and spring tensioner to keep the tracks taught. 6 - Flimsy looking but should take a body and a turret. 7 - Close up of the torsion suspension. 8 - Close up of the spring tensioner 9 - Ebay for motors and controllers :-) The suspension needed completely switching around as it was too tall and not working as it should, so the beams are now horizontal instead of vertical. This meant the spacing was all wrong. Several hours later... 10 - Prototype number 2. Lowered suspension and more wheels. No spring tensioner. Taking ages to get it how I want it to look. 16. Lowered suspension 17. Suspension close up 18. Re-geared 19. Quick release battery pack :-) 20. Close up of suspension...way too much twisting already, considering it's just a chassis without its main weight. 21. Turret turntable structure. Motor contained in the chassis with battery pack at front to counterbalance weight. 22. Turret turntable structure. 23 - Turntable motor mounted in the chassis, with temporary plates to check clearance. 23a 24 Turret motor mounted in the chassis. 25 - Quick release for turret battery pack. 26 - Turret battery. 27 - Turret turntable dimensions. 28 – Studless is too flexible in one direction and the chassis was sagging at either end with the battery packs, even before it has a body. Had to reinforce with studded bricks. It's a botch job though, as I didn't want to take the base apart for a third time. 29 360 degree rotating turret and elevating barrel. Pleased with the packaging of the battery pack with quick release connection. The infra red receiver is not in its final place though. Barrel elevation is pretty slow, but significant at the barrel tip. At the moment, it's not actual barrel looking ;) Added some lights at the end of the barrel just for fun. Here are the pics... 50. - Linear actuators to lift the barrel on a pivot, making a slow but very high torque lifting arm....as I guess the barrel will be quite weighty when built. 51. - Simple lifting mechanism with worm gear and clutch wheel. I need to add some stops so that it cannot over extend up or down. 52. - Another angle. 53. - and another 54. - Like the film Robocop, when they had the prosthetic arm...."Ok...attach it to his shoulder" ;) 55. - Ignore the temporary fixings....they are just while I make very quick adjustments before the final bushes go in to place. 56. - Looking pretty cool. Need to research a suitable barrel length once I've built the turret cover. 57. - The barrel motor and gear pivot vertically on its turntable to make a quick release mechanism.....very handy while adjustments are made. 58. - The 'frame' that attaches to the turntable with two quick release pins. 59. - It is also fixed to the main gear by just 2 fixings, and can be moved along the black rail while, so that the centre of gravity and balance can be finely tuned once the structure is complete so that it moves smoothly and unstressed. 60. - The battery box provides a little counter balance, but nowhere near enough once the barrel is built. On quick release fixings. The receiver will probably be moved once the rest of the turret is made. 61. - Close up of the quick release mounting points for the battery box. 62. - And lights :-) 63. The remote From left to right: turret swivel / unused, left track / right track, Barrel elevate / Flash lights Taken all my thinking, but I now have a functioning gun :). Really pleased with the tidy packaging. Lots of gearing allowed use of a compact motor, which I managed to slip into the barrel housing...looks pretty good. The firing mechanism uses springs (really strong ones from the Unimog suspension), pushed back with the use of cams, which when passed their maximum point allow the springs to push back, with a firing pin to hit the projectile. At the moment, I need gravity to push the projectile back against the firing pin, though vibration also helps. I need to figure out a method to do that automatically. Various quick access lids allow the loading of weaponry very quickly, and access to the firing pin which occasionally detaches from the spring piston due to the force. The ammunition fires about 5 metres when the barrel is tilted to about 30 degrees. The motor keeps the cams turning and so the gun keeps firing. The reload lid might be modified to make a gravity fed auto-loader :) Really pleased with it, just need to find a way to fix it to the turret now. Common sense would have said get the dimensions required first and build the gun....but hey ho ;) 64. - The ammunition is in the foreground with the yellow firing pin exposed by the hinged yellow access cover 65. - Beginnings of the barrel 66 - the ammunition ;) 67 - From the barrel tip looking back towards the firing mechanism. Length might need adjusting once mounted. 68 - Packaging of the motor, and half of the gearing 69 - Gearing down to increase torque to be able to push against 2 strong springs. 70 - Reverse side showing further gearing down. It makes for about a 5 second reload time. 71 - overhead showing the springs and the firing pin 72 - Yellow hinged access panel in its closed position, while the reloading panel is up for re-loading. 73 - Underside showing the motor connection passing underneath the cams, then outside on both sides then back inside to turn the cams. Short clip of the firing action and the cams....using a previous set of springs. Now uprated and much, much stronger :) http://youtu.be/L5MOa_urw_M You can see that the centre of gravity is way off now...so I'll need to ballast the rear and strengthen the turntable supports underneath. Looks pretty cool though :) 74 - Had to make the base of the gun wider, which is a shame as the packaging was so tidy. But I guess it makes sense anyway, as it tapers to the end. 75 - The motor driving the linear actuating lifting arms can lift it no problem, but struggle when going down. Need to look into that. 76 - 77 - Notice the complete lack of ballast to the right. Still turns around though :) Packaging and strengthening. Tried swapping the cams for a 3 pronged rotor to speed up repeat firing. It worked....for 3 minutes, then disintegrated, pictures to follow....as well as a pretty twisted axle. I never realised there is so much stress on some of the parts. Trying to get things to fit while still keeping the motors in position proved too difficult and having to use several universal joints to move the motor drive around obstacles. Sadly the neat packaging of the motor underneath the cams had to be abandoned as this created problems when I figured out a method to encourage the weapon back on the firing pin as it retracted prior to firing. But the results are pretty pleasing. I now have the final position of the gun barrel on the turret, with decent elevation possible. And used 2 battery packs as ballast at the back of the turret. This has taken too many hours and been pretty annoying just figuring out problems rather than building stuff. But hey ho, that's where the satisfaction comes in I guess. Now going to remount the turret to the chassis after strengthening it some more lol. Total time, bearing in mind it's from scratch, and with all the problem solving that goes with it, meaning lots of dismantling, relocating, mending....probably about 30 hours. 78 - Changed much of the red to black on the gun. Relocated the motor to behind the gun. I think it's lead to less 'backlash and better connectivity. Battery packs slotted on to each side for ballast. Only one is used, the other is 'spare'. The remote receiver will probably be moved. Picture shows maximum elevation angle. 79 - Reverse side shows gearing and chain driven weapon 'encourager'. 80 - Back view showing battery holders on sliding axles for easy changing. 81 - Chain drive linked to firing mechanism, turns tiny cogs backwards in the chamber which results in the weapon gently but insistently urged back towards the firing pin as it is drawn back by the springs. Pretty cool in my opinion ;) 82 - Close up of the chain drive to make the small cogs turn rapidly. 83 - Weapon loading cover up, showing the small cogs that spin backwards rapidly, making the weapon constantly stay in contact with the firing pin as it retracts :) 84 - New mount in the chassis for the turret, now much lower and improves CoG as well as rigidity. Also changed the gearing to make the turret rotate more quickly. 85 - Turret mountings 86 - Overhead of turret gearing. Very simple really. 87 - Shows the lowered turret mounting plate. 88 - Close up of the turret mechanism 89 - All put together so far. About 60 cm in length. All controls working so far, except the drive motors slip on the cogs.....need to fix that properly, perhaps replacing studless pieces for studded pieces. 90 - Is the barrel the correct length for the tank? I'm not sure. 91 - General angle 92 - Temporary controls and the main weapon. Will replace the drive controls (left hand side) with the wheels again I think. Middle green is turret rotate. Black with attachment is for weapon firing (one direction locked), right hand side elevates the barrel. Need to find a way to speed up the barrel elevation, but the gearing is already pretty tough on the little motor. Might have to replace with a more powerful one. 93 - Broken pieces. :) I've built a machine gun, and love the movement and sound, and would dearly love to put this on the tank, but the scale is so wrong, I think it has to stay as a silly toy. 94 - I will see if I can miniaturise further and mount it. Great little weapon. The gun is set up to continue firing, whether or not rounds are loaded. This was so that if I can figure out a way to get the auto loader to work, it's ready. But I'm having a mental block on the auto loader at present Due to the enormous amount of parts required, and it still flexing too much, I have completely replaced the studless chassis with a studded chassis. Took a while, but it's now strong enough, and still looks great...most of it is hidden behind the wheels and tracks. Also reworked the drive motors, more simple fixing and no gear slips now. Very solid drive, and also ready for 2 motors per track (front and rear) if necessary. - Trying to figure out how to make light covers that switch from uncovered (i.e.. white) to night vision red. Sad or what eh lol. Strengthening the turret elevation fixings now as they are the weakest point. - add lights, because I can - make a proper cover - I thought about making a gyro stabiliser for the gun barrel, but that would add too much weight, and perhaps be a bit too much geekery. I'm trying to figure out an auto-loader, and investigating a conveyor belt feeder. I built one last night, and it works pretty well, but very crude and very heavy and not really suitable for mounting on the barrel. Ideally I'm looking for some way to store and load about 20 rounds of ammunition, either with a remote to turn the loader, or chain/gear driven linked to the trigger mechanism. There is an elegant solution out there....I just need to think of it or find it lol. I'm sure there are far better ways of making the gun fire and raise and lower etc., more compact and more efficient. That's my lack of engineering showing through in that I'm struggling on what are probably basic concepts. It's great fun figuring stuff out. The gyro stabilising idea comes from the stabilisation in my camera lenses lol. But I think the speed the wheels would need to turn at (considering they'd be so small) to have a stabilising effect would be horrendous. I'm only guessing. Any other wish list things you'd like to see on this tank. There's quite a bit of space to play with as it's rather large. Update... Chassis stiffer thanks for studded parts. Added another pair of cams to the firing mechanism, at 180 degrees to the first pair....this now doubles the rate of reload....very simple really. Double the springs, now using all 4 springs from the Unimog suspension. Very, very stiff now, so now using an XL motor that has double the torque. Should make for a far more powerful weapon. Now it seems the weak point is the axle holding the cams. It it bending under pressure as it is forced to press against the springs, making the cams slip too early on the springs and giving a very weak level of firepower. Will work on that. 95 - Tried fitting some covering panels to see what it looked like. 96 - With the machine gun added, it just looks silly, though its firing mechanism and stuttering sound are excellent. 97 - now with a studded chassis. Much stronger if a little old fashioned....and a whole load less Lego pieces. 98 - Studded interior chassis with a yellow line for interest lol. 99 - Even without the turret, or battery packs, the torsion beams are under a lot of load. Might have to shorten them to make them stiffer. 100 - close up of the twist on the torsion beam, just supporting the chassis weight. 101 - LOL this is my very crude attempt at a belt driven ammunition loader. It holds 21 'rounds'. Too heavy, too cumbersome, and too ugly to go near being used on the tank. I'll make a little video of it in action before taking it apart. Mad idea consigned to the bin. I have a better idea forming though :) 102 - 103 - The upgraded firing system. Now wider to accommodate the 2 additional springs. I like how it looks, but the cam axle is bending and releasing the springs far earlier than their maximum recoil. If I can fix this, I think the power of the firing pin will be huge. (The black springs were temporary just to prove the concept) 104 - Upgraded motor with twice the torque of the original. The gearing is unchanged. Axles are longer though to cater for the increase in width. 105 - With all 4 springs from the Unimog. Very strong. 106 - Overhead shot with the service cover removed. 107 - Underside showing the additional pair of cams. Frustrating as it's all set up for an auto-loading system....I just haven't got that bit sorted yet lol. Finally, I've done it. I've figured out a way to remotely reload the ammunition. It's a gravity fed magazine, like a semi-automatic pistol, but upside down, and fed by gravity instead of a spring pushing up. Using a servo motor to pull out two retaining pins after each shot releases the next projectile into the firing chamber, then the pins insert into the one above. holding it back. And so on and so on. It doesn't look the most elegant of designs....I'd much rather have a spring loaded mechanism like a pistol, feeding from underneath, but i've run out of brain power and effort on this part of the build. 108 - Servo motor attached to gun, which pulls out the retaining pins allowing the 'rounds' to drop into the chamber 109 - Other angle showing the firing pin and the top of the barrel open. 110 - The cartridge holding the yellow ammunition rounds. Just a lattice work holder....might make this a little better at some point. 111 - The slider moving the retaining pins in and out of the ammunition, allowing a round to drop into the chamber and holding back the rest, thereby holding the weight back from the round below, allowing it to be fired. | Video of the reloading and firing mechanisms in action....not bad, clumsy looking though. http://youtu.be/bQ1rcX_MBEw You can see the last round being urged backwards towards the firing pin. Notice the yellow bush to the right hand side moving backwards, showing the position of the firing mechanism in its cycle, just about to fire. Much 'unbuilding' and rebuilding, but not actually creating anything new. I've rebuilt the rest of the chassis with studded pieces as it just wasn't taking the strain well enough. I've redone the torsion beam fixings, and shortened the beams to make the suspension stiffer and therefore sag less. I've redesigned the mechanism to raise and lower the turret a little quicker and have less strain on the motor, which has been replaced anyway with a larger motor with more torque. The mechanism now sits underneath the turntable in the chassis and the turning axle goes through the turntable which is pretty cool. Moved the turret further back on the turntable improving the CoG. The biggest change is in the driving and steering mechanisms. Previously it was a simple case of one large motor per rear wheel, which would either drive forwards or turn. It was very very simple and did the job in a very unsophisticated manner. Steering was either on or off, which I didn't like. So I built a new mechanism that has three differentials and 3 large motors. Two motors power a single drive shaft with plenty of torque, and then split to power each side. Before the drive axle reaches the wheels it passes through another differential where a motor either speeds up or slows down one wheel, thereby giving a steering function. Gives a fantastic level of control. But, not enough torque reaches the wheels to turn them. Either the gears jump, the pieces come apart, or there just is not enough torque. Immensely frustrating and has caused me to stop for a few days due to being annoyed at it lol. I've done 5 iterations now, each one slowly improving, but never quite giving the right result. I've video of them working off the chassis, and it looks brilliant. The last one is good now in that it cannot come apart, nor can the gears slip, but there is not enough torque getting through. So I need to reduce the gears one more time and try again. Watch this space. I'm desperate to get this part done, then mount it all and start to dress the tank to make it look more tank-like lol. Or I can just leave it as a chassis. Some pics and video of the drive and steering... Works and looks great on the bench, but does not work efficiently once installed into the chassis. While suspended, the tracks move as expected....but as soon as they have to take the weight of the chassis, they give up and will not turn. Need to reduce the gearing. 112. version 1 with studded Lego bricks. Two motors on the left provide the drive, transmitted to the right hand side via the single differential at the bottom left. (The very bottom cog and yellow spinner is just to balance the pressure on the differential cog...and free wheels.) The middle vertical 'layer' of cogs serve to split the power to left and right tracks evenly. Each 'shaft' passes through a differential, controlled by the 3rd motor which manages the steering by slowing down or speeding up your chosen drive shaft. 113 The studded bricks just came apart with the stresses, so switched to enclosed studless pieces. Much more resistant to coming apart. Slight move around of motors. Drive from 2 XL motors, steering from 1 L motor, which should have been fine when in motion, but was never enough to turn the track on it's axis like a tank should. 114 Overhead showing the gear configurations. 115 Version 3 with an XL motor to manage the steering. This should be more than adequate, but still cannot turn the tank easily. Makes me want to ditch the idea and go back to just one motor per track and be done with it. 116 Different angle. I've reduced the number of cogs as much as possible to reduce torque wastage, and made 2 cogs free spinning cogs to reduce wasted power even further. Still not enough power gets through to the tracks however. 117 Underneath to show the set up of gears. I've since changed this again, moving the main drive shaft from the end to the middle, hopefully allowing the power to split more evenly. I still need to add a further layer between the drive shaft and the steering part to reduce the drive gearing further. Videos: Version 2 - Fixed casings to prevent gear slip. But the steering motor kept pulling itself out of position. http://youtu.be/lps3-i_lLRE Version 3 - Same principle, but more secure fixings and better location for the steering motor. http://youtu.be/JoXga-ykBY8 My reason for a differential connecting the 2 drive motors is to allow motors of differing power to combine their torque to drive a single drive shaft without damaging driver the weaker motor harder and forcibly reducing the torque of the stronger motor. Even two motors the same will have slightly different power levels. However, what I realised finally in a moment of clarity and simplicity over complexity is that I'm using 2 motors to drive one shaft, which is then split to power 2 drive shafts. Madness. So, I've removed that differential at the beginning and now each motor drives its own shaft into the steering mechanism and straight to the tracks. Much less friction, much less gears, and I've even been able to increase the gearing as a result. The steering mechanism is unchanged and now also works ok. If there is any difference in motor power between the two XL motors, I can fine tune the steering to compensate for this and even them out. Packaging is improved as there are less cogs and gears in the way. Torque to the tracks has been increased....and my satisfaction factor has improved too ;) Now just strengthening that little area, then its time to mount the turret and gun and start to build the body around it....mostly aesthetics :) 118 - Old drive configuration mounted in the chassis. Two motors driving one shaft, splitting into two drives. Finally I saw the logic, and removed a whole load of unnecessary complexity. See pics 120 onwards. 119 - Another angle of steering system in the chassis. 120 - Final configuration (I hope). Two motors at the top, driving two shafts, then modified by the steering system. This in an underneath photo. 121 - Overhead. Looks relatively simple now. Always a good sign. 122 - From the rear. Note: All the 4 bladed yellow and black rotors are simply to easily show me which way the axles are turning. They serve no other purpose. I quite like the idea of the rear of the tank having the two black rotors spinning on show. Depends on what plans I have for the rear end. 123 - Side angle showing (or not showing) the removal of all those gears. Even though two of them were free wheels cogs, they still made the thing awfully weak. Notice now the lack or gear reduction until the final 90 degree gear meeting the driving axles. 124 - Turntable with mounted turret, in position in the chassis. The barrel elevation system now passes through the turntable. Motor is mounted vertically underneath and inside the turntable. Turns the grey worm gear, which turns the gears on the linear actuator to raise and lower the barrel. 125 - Front view of the barrel elevator. 126 - Rear view showing the small gear turned by the worm gear, driving the gears to raise and lower the barrel. This mechanism has resulted in no stress on either the raising or lowering of the barrel. Result :) 127 - Directly behind showing the workings of the barrel elevation system. 128 - Another angle. That’s all for now.