rgbrown

Agree with the last piece of advice (experiment in small steps), but I seriously doubt PF uses a linear regulator (e.g. a 7805) to power the control logic, as that would be highly wasteful of battery power. It probably uses a small buck converter. There will be some nominal input voltage range that the receiver has been designed to work with, going above that is probably not a good idea. That range may well be quite high, but who knows. Anyone got technical (electronic) specs for the 8884? As has been mentioned though, only the switching logic works at low voltage; the PF supply and control pins will always be at 0/9V (or whatever you're running it at)

Gee, yours sounds ill ... are you sure your batteries aren't flat? And also, did I hear skipping gears in your video (sounds a bit like popcorn) ? Yours surprises me, because it even struggles with jobs like lowering the boom.

Certainly very quirky! I like all the tricks that it can do. Two little comments: * You could free up one motor by using a Cherry-picker style boom unfolding technique, which would also avoid the issue of the thing waving around like crazy as it unfolds * Is there any way you could make the lower boom section more visually substantial? Currently it makes the boom look a bit top-heavy... Don't get me wrong though, it's a very fun model! p.s. White-wedding in midi?

An idea: I'm not at home this month, so I can't test it, but it would be relatively easy to devise a test system to see whether linear actuators are deteriorating (or variable in performance). The idea is to apply a constant load and constant torque to the actuator and then to time how long it takes to extend or retract. Constant torque can be provided by coiling a string around a wheel-hub. If the theory that the LAs are deteriorating is correct, the extend/retract time should be longer for a used one than for a new one. I don't know off-hand how big the weights should be, but it should be pretty easy to sort it out by experimentation. Alternatively you could measure the torque required to make the LA move, and compare. I've attached a picture of how you might do it to measure the retract time. You'd need to change the LA orientation to upwards to measure extension time.

@Fyredog, CP5670: There was some debate earlier as to whether it would be better to simply use 1 actuator. Load reduction, and hence reduction on wear is the argument for using 2 parallel actuators (so long as you can balance them)

Not possible for 8043 as there is not enough space, but more generally, the two outputs of a differential could be used two drive two parallel LAs, which would make the configuration self-balancing even if one started slipping under clutch, etc.

Surely just moving one of the grey idlers across to the other side of the LA bracket would eliminate that particular problem. (edit. Seems jetlag has affected my ability to read this forum. This idea has been well and truly covered off already! Sorry for being dumb. I have an 8043 in my suitcase, taunting me. Bought it in US (179.99), now in UK, not home (NZ) until September)

I just had a similar experience at the Hillsdale Mall Lego store. Picked up an 8043 for $179.99 (+ tax). It was mispriced, showed up in their system as 199.99, but of course they honoured the ticket price. There may be one or two more left there.

+1 New Zealand. Pet peeve about being here: there is an NZ S@H store, but shipping is prohibitively ridiculous. To buy a smallish set, e.g. 8047, costs NZD45 to purchase and NZD50 to ship!

This set was my first technic set in about 15 years (My wife found it exceedingly cheap for about 35 NZD (approx 20 USD) on clearance). I very much enjoyed building it as it was my introduction to studless building, and the first time that I had used things like driving rings and the new (since ages ago) bevel and double-bevel gears. The play value is less good ... raising and lowering the arm is hard work on the fingers. I haven't yet motorized it, but I have a motor now, so I will if I can be bothered rebuilding it sometime. The backlash in the steering doesn't bother me, as it is pretty easy to steer once in motion, and has a tight turning circle. The steering should, however, be geared down a bit, the required torque to steer feels uncomfortable. The Ackerman steering is a nice touch, but is also the source of the backlash due to the play introduced by the multiple non-friction pins in the linkages. The stabilisers don't do much, however it's (possibly) better that they're there than not at all. To me the model looks good, apart from some injudicious colour scheme choices. The B-model, though, is unpleasant to use and not that much fun to build. 8295 has a good selection of parts including a good number of gears. Nothing interesting like diffs though. Since then I've bought 8259 (mini bulldozer) and 8292 (cherry picker). I prefer the building style of the Cherry Picker designer, seems a bit more tidy and organised, where the 8295 feels a little haphazard. The end result does look pretty good though. Personally I found the 8292 a more enjoyable build. To me though, if you had an option between large sets 8295 and 8265 (front loader) at similar prices, the front-loader would win hands down. Better part selection, more interesting design. But the 8295 is hardly as bad as everyone says it is. my tuppence

Nice work from the 8yo's teacher! I would guess that a number of the undergrads I teach couldn't do that without prodding. Dang, I'm supposed to be writing a paper at the moment, and you've got me stuck thinking about this :) I'm with you now, wasn't sure if you were talking about the temporal behaviour of the engine. I'm trained as an engineer, but I'm now a mathematician so this is good fun for me. In fact I'm feeling like it would be fun to create a computational model of this thing - first the CVP feedback loop, then the engine. However I don't have enough pneumatics parts to work out model parameters (e.g. I have no compressor or large actuators or studless valves -- will have to convince my wife to get me an 8049 next year) So ... are you up for some experiments? A start would be measuring the force produced by your valve arrangement for a constant input pressure over its full positional range, you could just measure the force produced by a big or a small actuator. Anyway, let me know what you think cheers, Richard

Very nice model! I'm intrigued ... I would love to see a short video What happens if you remove the dithering? Does it just lock up? Not sure I quite understand what you mean here -- what do you mean by differential and double differential of position? cheers, enjoying your work! Richard

I'm sure Jetro wasn't intending to cast aspersions on my person , but just in case I'd better clarify my position. Personally, I have no objection to Blakbird selling instructions, even for profit. It's a legitimate means of making money, although if intended as a money-making venture there are probably some issues regarding whether it is appropriate to advertise here. I for one, will not be buying the instructions. I don't have the parts, nor can I afford them right now. However, from what he has said Blakbird is simply trying to recoup some of the costs of developing a resource that is valuable to the community, but not so much to him personally. He has already contributed enormously to the community, gratis, and I'm guessing that he hasn't any philosophical objection to releasing the instructions to the world at large, except that it is really not worth his while. (I know the value of time - I have four preschoolers, there's no way I could invest dozens of hours in a project that didn't have some kind of realisable benefit to me) All I was doing was putting this model of selling out there, as an example of something I've seen used successfully before (www.tramy.us) -- the website explains the philosophy too. I was not recommending Blakbird necessarily adopt this strategy. In fact, there are a few reasons why it may not be appropriate here: The unit price is moderately high, leading to purchasers feeling "ripped off" when it becomes freely available There may not be sufficient demand to sell enough copies at a lower price to recoup the expense It really needs to be specified that it's being done this way from the outset so everyone understands what's going on The issue remains, though: there are numerous talented people in the Technic community who can contribute resources that are highly valuable to the community at large, but that would need financial support to do be able to do so. How best to achieve this? As has been evidenced by this thread, there are people who are willing to front up money for quality resources, so it would be awesome if an acceptable solution could be devised. By the way, since I'm writing in this somewhat provocative way and since none of you know who I am, I should semi-introduce myself so as not to be rude. I'm a mathematician in New Zealand, and I'm just getting back into Technic for the first time since childhood (my last set was acquired when I was 9 - the flex system universal set). I find this community, and the quality of the MOCs amazing -- I've been lurking invisible in the forums for quite some time. Blakbird's Technicopedia is an incredible resource, and he deserves all the support the community can give him. phew :)

How about the idea of a world price, which I have seen before in the OSS world. The idea is that Blakbird would make an estimate of the value of the time spent to make the instructions (the world price), and nominates a unit price (i.e. $25) for the instructions. Once the cumulative sales of instructions add up to the world price, or a specified period of time has elapsed, he would then release them into the public domain. That way Blakbird doesn't make profit from them, which he has said is not his intent, and the relevant sector of the LEGO community effectively sponsor the development of something valuable that otherwise wouldn't have been done. my tuppence, Richard

It is absolutely reasonable, what an epic job!