johanby

Has anyone tried to use an other (than 8887) 10VDC charger for the 8878 rechargable battery? Results?

I can recommend Flowol http://www.flowol.com/

Sorry for going slightly off-topic: I have managed to find PDF files of most of the old idea books, but have so far failed with finding "Das grosse Lego buch" nr 239. http://brickfetish.com/ideas/239/239_1968.html Has anyone seen it scanned somewhere on the web and feel like sharing this information?

I always thought that there was some kind of PWM system to regulate the power delivered to the motor, from the 8878 battery or the ir-receiver. Hence there is no (resistive) power dissipation that needs to be cooled off. But I actually have no idea how this is implemented or if this is the case.

I have tried the same, but find that the new wheels with technic axle connection (e.g. http://www.bricklink.com/catalogItem.asp?P=55423 ) have trouble staying on the blue track, especially on switch points. I wish there were similar wheels like http://www.bricklink.com/catalogItem.asp?P=wheel2a but with technic cross axle connection instead. Actually, the adapted motor you refer to as a 9V motor is the newer 12V type motor http://www.bricklink.com/catalogItem.asp?P=bb12v . However, this does not change any of your conclusions. I really like what you have done and will try it myself.

Two of the remote controlled racers (8475 and 8366) from 2002/2003 have a control unit called "RC Receiver Unit with Auxiliary Output (6272)", see http://www.bricklink.com/catalogItem.asp?P=6272c01 or http://www.peeron.com/inv/parts/6272. The control unit has a red connector which is connected to two RC race buggy motors 5292 (in parallel), but also one extra grey colored output (I guess that is the auxillary output). I can control the red output with the remote control, but nothing happens when I connect the grey output. Does anyone know how to control this output?

I am not so sure I will call it a momentary output. It works fine and deliver a constant output, as long as the load is not too heavy. I.e., if I stall the motor connected to the auxiliary output, the unit seems to cut the current at some limit. Thus the output seems current-limited compared to the regular output. For instance, if I connect the two 5292 motors to the auxiliary output, they will run freely as long as the car is not on the ground (no load), but as soon as it is put on the ground, the car will almost not move at all. However, I agree that the conclusion must be that the auxiliary output should be used to simpler tasks like gear shifting.

Ah, I never noticed them before (on the back side of the controller.) Thanks!

Yep. I cut away the macintosh connector and soldered a female serial connector to the wires according to your instructions. Will try the interface this evening to try to get som life in it (at least the on-connector works). Thanks for all help!

I too got my unit second hand, however with a macintosh cable which is totally useless for me. Therefore it is very valuable to hear that the serial cable should be of null modem type. My problem is though that all null modem cables I have found so far have female connectors in both ends (in order to connect two computers). Since the interface also has a female connector, I guess the null modem cable needs to have one male and one female connector. Is it possible to find such null modem cables or does one have to solder it by oneself? Another questio: Did anyone try this software (Flowol http://www.flowol.com/InterfaceLEGOB.aspx) for interface B?

Yes, that sounds correct. One (straight, but I guess also the center of a curved) rail piece is 16 studs. A full circle consists of 16 pieces, i.e. 256 studs. Thus the diameter of the center would be about 256/pi =81.5 studs.

I think the 9833 Adapter is an AC adapter and thus not suitable for the 8878 battery. See http://cache.lego.com/downloads/Education/...e2010School.pdf page 27. By the way, I use a 12V/500mA generic adapter (positive center) with good results for the 8878. This is however something you do at your own risk if you want to try...

Because of stressing the bricks/studs/etc in a destructive way. See http://bramlambrecht.com/tmp/jamieberard-b...stress-bf06.pdf

So I guess the only way to change the stiffness of a spring is to change its length. A non-destructive way would be to make combinations of springs in series or/and in parallel. Two springs with stiffnesses k1 and k2 would then have an effective stiffness k1+k2 in parallel and k1*k2/(k1+k2) in series. A destructive way, but with more freedom, would be to cut the spring (gives a stiffer spring) or add extra pieces (gives a less stiff spring, however care must be taken so they not overlap (sit in parallel), effectively making a stiffer spring). On the other hand, this procedure also changes the precompression...

That is the key point! Thank you for a very good explanation, now this makes sense to me. Obviously, the precompression only moves us to another point on the force-displacement curve, with the slope/stiffness being the same. So it means that the constitutive equation instead would be F=F, for F<F0 F-F0=kx, for F>F0

Well, this is where I disagree. All materials (OK, most materials) are linear elastic. That means that an applied stress (i.e applied force for constant cross section) will yield a (compressive or tensile) strain (and thus elongation/compression) which is proportional to the applied stress (the so called Hooke's law). To precompress the spring will not have the effect that you need to reach some limit stress/force until a strain/compression will appear (since that would mean that the material was not linearly elastic). An applied stress/force on a pre-compressed spring will be compressed, however not as much as on the spring without precompression. This means that the spring (assembly) is effectively stiffer. It is easy to test by hand.

Yes and no. The total force required to fully compress the spring would be the same with or without the bushing (I guess the masses 600g, 1300g, etc, indicated in the picture above was the the corresponding force to fully compress the spring). On the other hand, the total travel distance decreases when inserting the bushing. Hence the stiffness (i.e. the ratio between applied load and compressed distance) will increase. Therefore the spring will be stiffer, but it cannot carry a higher load until fully compressed.

Of course this power difference will only be noted when standard (non-rechargeable) 1.5V AAA batteries are used. Rechargeable NiMH AAA batteries have a voltage of only 1.2V yielding a total of 7.2V, even less than the 7.4V of the 8878 LiPo battery.

Taking all solid mechanics issues aside, there is of course another problem. A wheel with 30 mm diameter would need to rotate with about 14000 rpms to achieve a speed of 80 km/h. A bigger wheel would of course need less, but still a wheel with 60 mm diameter would need to rotate with 7000 rpms. The XL motor would need an upgearing of about 32:1 and the race buggy motor would need an upgearing of about 5.4:1. Heck, even the high rev low torque 2838 motor would need an upgearing of about 1.7:1.

Interesting! I suppose you use the 4.5V motor or is it the 12V motor? Are you having the battery on full voltage (7.2V) or did you choose a lower voltage? By the way, does anyone know how high voltage is it possible to use on the 4.5V motor without damaging it?

That depends. For me, the blue rail has significant nostalgic value from my childhood and I prefer using it over newer rails. On the other hand, it works best with the trains from that period and also takes more time to set up. Moreover, my Emerald Night tends to derail in the blue points, but as long as you don't use points, it works fine on the blue rail.

Is there a certain reason why the acronym V9 is used? AFAIK, it is only when talking about money one puts the unit before the value, i.e. £4.

You are trying to find 8466 on S@H? I guess you are meaning the 8297 Off-roader, which in my opinion is way inferior to the 8466 Off-roader from 2001. Or are you planning to buy the 8466 on Ebay? If not, I would recommend the 8265 Front loader over the 8297 Off-roader.

What about using the x928cx1 hockey slap shot spring instead of using the axle as a torsion spring (to avoid the tension)? This has been used for example in return-to-center-steering, see e.g. http://technicbricks.blogspot.com/2009/09/...-to-center.html

More specific, what does the 8887 charger actually contain? Is it a regular 230VAC -> 10VDC adaptor or does it contain any "intelligence" for charging?