Mindboards

see the PS in my post above...

jojoguy14 wrote: Since there is only 1 "Port 4", I don't see how could connect more than 2 NXT's via RS-485

You don't need a multiplexer, but you do need to be careful not to have more than one NXT send a message at any one time (as has already been mentioned).

A bit of google searching will show you what I mean, for instance, in this video there are 3 NXTs connected over the same RS485 bus

http://www.youtube.com/watch?v=Kg56R6XzVdA

Matt

The port splitter I mention above is basically an alternative to taking a knife to a bunch of cables...

That's a very interesting video! I'm curious though if it's even POSSIBLE to make a NXT-G block for RS-485. Hmmmm...Anyone good at Labview that can tell us?

jojoguy10

I am sure it is POSSIBLE to make it work with NXT-G (and enhanced firmware). If you want to use RS485, I would suggest learning a different language (NXC is really good, and obviously RS485 works with it).

The Lego factory mentioned in this site http://www.thenxtstep.blogspot.com/ is apparently controlled by 5 NXTs. No mention of how (or even if) they are interconnected but a bit of research into that project might shed some light on the subject.

jojoguy14 wrote:Hello there!

Does anyone know if it's possible to have more than 4 NXT's in a robot? I mean, you can have up to 4 connected through bluetooth, but is there some other way (bluetooth or other) to connect more than 4 NXT's? RS-485 maybe?

Jojoguy10

I been following this, though it does beg me to question. Is this theroy or you building a bot that will need this many NXT? It seems that IF you have 4-8 nxt at hand then this topic has merit since getting all these to talk to each other would be nice. If you have say only 1 or 2 nxt, then you plan to buy all these bricks? It would seem that this going to be very very heavy for a single bot to carry. It would seem better to use 1 nxt and use the motor Mux(nxtmx), saves weight. Rather easy to program and no issues with packets. Just the batteries for all these bricks will weigh a ton. 1 battery pack can run 4-5 Nxtmx's very easy. this gives you 13dof with one NXT.

Though not said this may be a "swarm" project?

anyway im just toss out some of my thoughts here and no answers...

Doc

aagruntpuddock wrote:The Lego factory mentioned in this site http://www.thenxtstep.blogspot.com/ is apparently controlled by 5 NXTs. No mention of how (or even if) they are interconnected but a bit of research into that project might shed some light on the subject.

How about a specific link? I think though, that you are referring to the project Xander helped with. Yes, he did use RS485 between the two NXTs on the robotic arm he programmed. Other than that, I assume "they" used BT for any interNXT communication.

Edit: Go to Xanders blog, is that the one?

EDIT: I did not realise there were a page two and simply repeated some info already given. Sorry for spamming.

jojoguy14 wrote:

physics-matt wrote:

jojoguy14 wrote: So, you're saying I can do something like this:
[] = NXT
-- = RS-485
__ = BT

[]-----[]_____[]------[]______[]--------[]_____[]-------[]

The only problem with that approach is that each NXT can only talk to its neighbours. If you want one at one end to talk to one at the other end the message will have to be relayed, which will create a large latency.

IIRC, if you put all the NXTs onto a single RS485 bus, they will all be able to communicate to each other directly.

Matt

So...is RS-485 possible with some kind of multiplexer? Since there is only 1 "Port 4", I don't see how could connect more than 2 NXT's via RS-485

jojoguy10

Yes it is, see the following video:
http://www.youtube.com/watch?v=Kg56R6XzVdA

However, as described above and in the video, you cannot just plug in the cables and expect everything to work. The RS485 bus is like a classroom full of young kids (NXTs). They can all talk and listen, but if more than one talks at the same time, no one can hear anything.
You, the teacher, needs to make sure that only one kid (nxt) talks at a time and that every kid (nxt) listens and responds to the right commands. All this has to be implemented in the software.

noeyewar wrote:They can all talk and listen, but if more than one talks at the same time, no one can hear anything.

Umm, isn't that what Andy and I already said here and here?

- Xander