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Hrafn

Eurobricks Knights
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Everything posted by Hrafn

  1. Hrafn
    That's what I thought, too, until Saberwing40k posted this design, which I've built and found quite strong (other than some flex in the wishbones):
  2. Hrafn
    If you start by sandwiching a 3L differential between two thin liftarms, you can build an even-width suspension module.
  3. Hrafn
    If I'm reading Philo's page right, the LiPo rechargeable battery can't get the buggy motor up to full power, but the 9V one can. It's not clear to me if the 9V can drive two at full power. Does anyone know? Whether this is useful to the original poster or not depends on whether he or she has that box, of course. BTW, the page of Philo's I should really have cited is the power curves one.
  4. Hrafn
    Thanks, I appreciate it! I'll give it a go, though I'm worried about the bevel gears. I'm going to be running 2 buggy motors through this. EDIT: This works superbly. It's exactly what I was looking for, and the bevel gears have no trouble with two stalled buggy motors. Thank you so much! When I posted my request for help, I figured I might get some pointers and general advice, and maybe an example or two to look at. I didn't think anyone would solve my exact problem and give me an .lxf file to boot! I haven't decided whether I'll use the servo or an M-motor (geared down) for steering yet. Initial tests suggested to me that the servo lag is so long that (with my poor RC driving skills) I'm likely to crash a lot. Implementing return-to-center with an M-motor is easy, if need be. I'm also toying with the idea of variable ratio steering but I don't know if it will be useful or worth the extra complication and space.
  5. Hrafn
    I've actually been trying this same setup, and while as Saberwing40k said, the receiver will be fine, it won't work well overall. Philo has some very useful data at his motor comparison, battery comparison, and IR receiver pages. The conclusions from those and from experimenting are 1) One receiver can power at most one RC motor. You can plug in two, but they'll each operate at reduced power. 2) The rechargeable battery's overload protection kicks in really quickly, even if the motors are connected directly to it. One battery per motor might work, but since I only have one rechargeable battery I use a 9V AA battery box [to power two RC motors]. So far that setup works fine. Instead of using one receiver per motor, you can also route the power from the battery box through a switch to the motors. You can then use the receiver to control a M-motor which activates the switch. It's awkward, but it saves on receivers.
  6. Hrafn
    Oh no! I hope you get access to your old account restored quickly.
  7. Hrafn
    I'm curious to see it, since I do have those hubs but haven't been able to find a solution with them that's narrow enough.
  8. Hrafn
    In the top version, the wheel tends to fall right off the CV axle. In the bottom one, the axle pulls out of the 3L u-joint. Hm. This works, but leaves 2L+ of axle sticking out from the side of the wheel, which looks bad. I wish the tan 4L axles with smooth center section had a stop in the middle.
  9. Hrafn
    OK, the front suspension is coming along nicely (with caster, kingpin inclination giving minimal scrub, Ackerman steering, SLA suspension to improve camber in cornering). Now I'm having an issue with the rear suspension, which needs to be 21 studs wide (including the 62.4x20 tires), be driven, have a differential, and be a double-wishbone setup. The width rules out using 2 CV joints per side, so I was using 1 CV and 1 u-joint, custom hubs, and 5L liftarms as wishbones. The problem is that the wheels aren't held on robustly. If I put the u-joint near the wheel, the axle that the wheel is on tends to slip out of the u-joint, making the wheel fall off. If instead I use the CV joint near the wheel, and attach the wheel to the last 1L of the CV axle, the wheel tends to slip off the CV axle. Does anyone know of an existing solution to this problem? Widening the axle to 23 studs is not really an option if I am going to keep things scaled properly. Thanks! Oh, and could an administrator change the title of this topic to something like [WIP][MOC] 1:10 RWD Rally Car? Thanks again!
  10. Hrafn
    A huge box of unsorted parts is a problem I'd love to have! The servo valve is quite elegant. It will give not-quite-proportional control, since the axes of rotation for the servo and the valve are not in line, but that shouldn't be a real issue. In fact, I'm tempted to try adapting your idea to M-motor driven vehicle steering to give a variable steering ratio.
  11. Hrafn
    I'm impressed with the number of functions you squeezed into that space! The engine is nice, too. I would have thought that the plates with clips would eventually start sliding on the bar - do they hold up OK in real life?
  12. Hrafn
    I may do that myself. Just offsetting the a-arms causes them to experience torsional loads, which then requires me to reinforce them. Also, offsetting the arms by 1/2 stud makes adding a shock absorber a bit awkward.
  13. Hrafn
    The issue with that is you'd have to then put an axle through the ball to act as a suspension link, and loads along the length of that link would tend to pull it apart over time.
  14. Hrafn
    1900 RPM, according to Philo's very useful motor comparison page.
  15. Hrafn
    How long is too long? What wheels are you looking to use? Most cars have a wheelbase that's roughly 4 times the diameter of their tires. Can you put the L motor above or below (or to the side) of the servo and connect it to the driveshaft with gears?
  16. Hrafn
    How does this look? I don't know if the steering offset will turn out to be correct for Ackerman (or near-Ackerman) steering, and any caster angle will have to be created by offsetting the a-arms relative to each other. Otherwise I'm pretty happy with it; with 62.4 x 20 tires the turning point is under the tire, though not centered.
  17. Hrafn
    Thanks! Moving the top towball 1 stud closer to the wheel greatly reduced the camber issue, even when I then added a bit of caster.
  18. Hrafn
    Which is more important for steering: a kingpin inclination that puts the steering centerpoint near or under the tire, or some amount of caster angle? I'm having trouble achieving both with custom hubs without sacrificing performance in other areas. For the moment I've put together a few hubs with kingpin inclination but no caster; the second one allows the wheel to be steered around a point under the tire. The second one was inspired by Piterx's use of . I haven't added a steering link attachment point yet. EDIT: here's an improved version that keeps the lower arm from hitting the hub as you steer, and adds caster angle. The downside is that I get some negative camber at extreme steering angles.
  19. Hrafn
    Another data point: I ordered mid-January, got a confirmation email on January 21st and called them that day to pay, the order shipped a week later, and it arrived a week after that. So it's not a fast process (especially compared to BrickLink) but it did let me get parts that aren't available on BL or on store shelves in the US yet.
  20. Hrafn
    Mbmc, Nicjasno - thanks! I'll try getting rid of the 5x9 frame (or turning it 90 degrees and using one on each side, or using some other structural solution including maybe dogbone frames) so that I can get the rack properly aligned with the towballs on the hubs. One issue with using these hubs and tilting them for caster angle is that the optimum location for the rack is no longer an integer number of half-studs from anything else, which is another reason to try custom hubs where I can set all the relevant dimensions independently.
  21. Hrafn
    I realize it might be overkill, but I'm hoping to have this car be very maneuverable at the high speeds I expect its 2 RC motors to propel it at. My hope is that some of these variables (camber, caster, etc.) will help with maneuverability. Interesting! I hadn't really seen trailing arms done for front axles before. The vehicle I'm modeling has double wishbones so I wanted to stick with that. Thanks, I hadn't seen that one. I may have to go with custom hubs to get kingpin inclination. That particular hub decreases ground clearance by 1 stud over using the hubs I have now, but it could probably be adapted to improve ground clearance for my application.
  22. Hrafn
    Thanks. It looks like a big part of my problem is the gear rack location, which forces the tie rods to be angled.
  23. Hrafn
    I've been trying to build a 1:10, rear-wheel-drive rally car and am running into a number of problems. Right now the issues are with the front suspension and steering. I had hoped to have 1) short long arms suspension (for progressive camber with suspension travel) 2) some caster angle (to help with bump steer) 3) Ackerman steering (or close to it); here I'm using a three-piece tie rod [EDIT: adding a bit of longitudinal reinforcement fixed a lot of this, but I'd still like to hear what people think of the setup and if they have any suggestions] However, I'm having three two problems: 1) SLA suspension plus caster leads to terrible toe-in and -out with suspension travel 2) The tie rods are behind the wheels, and there is way too much play in the system (and some toe-out when moving forward). Some of this I know is due to my not having fully reinforced the steering rack assembly, but I'm not sure more reinforcement will totally fix it. Basically, the two-stud-wide rack assembly wiggles forward and backward a lot when you push on the wheels. 3) With aligned and equal-length wishbones, I get near-Ackerman performance; with this setup I no longer seem to. The wheelbase is 30 studs, and the current (tentative) design is below. Top (with the motor towards the front of the vehicle) Bottom (note that the 6L arms are offset .5 studs from the top arms): Any advice would be much appreciated. Or if you can think of other people's MOCs I should look at for inspiration, let me know. Thank you!
  24. Hrafn
    LEGO has a finite amount of resources, including manufacturing capacity and marketing budget and personnel. Normally these are spread across persisting themes (System, Technic, etc.) and limited-time themes (Ninjago, etc.). It's possible that the movie requires so many resources (again, manufacturing for tie-in sets, and certainly it is using marketing resources) that some other areas are suffering temporarily. That's just speculation on my part, but TLG has advertised some jobs recently (in the US) where the job description explicitly said they wanted people to help allocate resources between different efforts.
  25. Hrafn
    Maybe TLG is focusing on the movie and doesn't have capacity to put out the Technic sets in the US right now? It does seem odd.
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