Simultaneous RC Cars

[fridgid]

I'm working on an idea with my local robotics club (it's pretty green and strangely lacking EEs) on an idea involving multiple (I'd say max of 20, but 10 would do and for proof of concept I think were just going for 2-3) RC cars. Assuming each car needs at min, two channels to operate and to be safe I think 4-5 would be best, we're trying to decide on what kind of wireless tech to use.

I originally thought we could just get a schem or two of some wireless trancievers and build them, but after a lot of reading it seems that wireless communication is wayyyy out of my league for this project.

So, keeping in mind that we have very cheap labor / man-hours and would like to spend a little amount of money possible, what recommendation does the savy SoR forum have?

Idea's we've considered:

1) Hacking cheap RC car's and removing their RC cricuits.
    Seems doable, but I would assume they would have bad interference with each other. I have done this for single RC cars before though.

2) Buy premade trancievers such as ( http://www.sparkfun.com/products/10153 ) and building a circuit around them.
    These don't look like they're very simple to setup, and it's new territory  me.

3) Shell out the $100-200 for the big boy ones.
    Price!

[Resilient]

It is more expensive than the link you posted, but I use Xbee for almost all my wireless needs. I have found it works fairly well and there are several version available depending on your requirements.

[fridgid]

I saw those are sparkfun.

Do you know how well it handles multiple transmitters? Can you change the freq?

We're just planning on building 1-2 right now, but then scaling it up to at least 10 maybe even 20 of these guys, and I just want to be reasonably sure they won't clash with each others signaling.

[Resilient]

I have not yet used it for projects requiring more than a single pair, but I do know that it is possible and a quick look at the manual confirms that there are several different methods of setting up networks of multiple Xbees.

[Soeren]

Hi,

1) Hacking cheap RC car's and removing their RC cricuits.
    Seems doable, but I would assume they would have bad interference with each other. I have done this for single RC cars before though.

Very bad idea!
While they all have crystals in the transmitter, it's just for keeping the transmitter legal, but the receivers are usually not crystal controlled (to keep the price down), so running more than one at a time would be impossible.

2) Buy premade trancievers such as ( http://www.sparkfun.com/products/10153 ) and building a circuit around them.
    These don't look like they're very simple to setup, and it's new territory  me.

That would cost you $24 (as you need one at each end of the link) plus a controller circuit at each end and while they could be used for sending telemetry readings back to the user, they're really not made for R/C.

3) Shell out the $100-200 for the big boy ones.
    Price!

Well, the big boys toys can cost you as much as $2000!, but you're on the right track anyway... Just look at this $23, 6 ch. complete set (TX/RX) and tell me if it's worth your time and effort (and money) to go with option #2

They do have 2 and 4 channel types at the same prize and a pistol grip 2 ch. transmitter (still a set including a receiver) for $15.

This way you get certified sets that's made for the purpose, can be run without interfering with each other and at a price that's ridiculously low.

[Resilient]

I realize I might be a little confused as to what you are trying to do. Do you want the cars to communicate with each other, or do you want humans to control a lot of cars?

Because there are cheap RC transmitters that will be more than you need for just controlling the cars.

[fridgid]

I realize I might be a little confused as to what you are trying to do. Do you want the cars to communicate with each other, or do you want humans to control a lot of cars?

Because there are cheap RC transmitters that will be more than you need for just controlling the cars.

I'm trying to just have humans control RC cars in an event\contest. We're trying to work towards a annual fundraiser we would host that would be 'flashy' enough to get people excited to both join the club and donate money. Right now just a proof a concept, but eventually I'd like to expand it to something like 10 vs 10 max cars doing something with ball objects (tennis balls or maybe larger) and some goals. (Kind of a mesh between soccer and pool I guess. We were thinking a billiards-esqe table setup with pockets/goalsand a bunch of RC cars trying to knock each other balls off the table. Possibly later adding 'abilities' or 'specials' to the vehicles (aka extra channels) and the ability to 'disable' other cars or something.) Just starting though, so 2 or 3 RC cars able to push something small would be a good starting point. I just saw the radio thing as being a very big problem / money dump if we didn't plan. Just trying to do my homework

Thank you both for the replys, I'll look into them both. Soeren, would you recommend any particular frequency? Or does that even matter? I guess the IT person in me is hesitant to use something on 2.4 because there's so much stuff barfing signals on that frequency, but I guess so long as the transmitters handle that IDC. Also, I couldn't find a datasheet/manual for that link. Are you sure it would be viable for concurrent numbers up to I dunno, 20 max? Also, I didn't know they were that cheap. I thought they were closer to $40 per transmitter/receiver ($80 a set) that this changes things. Any other sites you'd recommend?

I would assume we would host the event inside a school with the likes of bluetooth/802.11/etc rampant all around us. Specifically the Eng building of a major university. If that could cause an issue.

[Resilient]

Go with something like what Soren suggested or something like this (which I find to be more natural for controlling rc cars):
http://www.hobbyking.com/hobbycity/store/__12177__HK_300_3_Channel_2_4ghz_FHSS_Ground_Radio.html

I don't know about the ground models, but the air models are typically good for up to 30 models at once. They all have different systems for doing so, but all the 2.4ghz systems for RC have a way to avoid frequency conflicts automatically. The old 72mhz days of having to make sure everyone was on a different frequency are gone (unless of course you are still using one of those old systems).

[Soeren]

Hi,

[...] Soeren, would you recommend any particular frequency? Or does that even matter?

The one you can get the cheapest (isn't that the entire purpose?) and no, it doesn't matter unless you're trying to accomplish something extreme (for R/C control that is).

I guess the IT person in me is hesitant to use something on 2.4 because there's so much stuff barfing signals on that frequency, but I guess so long as the transmitters handle that IDC.

I guess the electronics person in me wonders why you mention Insulation Displacement Connectors
And the HF person in me can assure you that a radio signal dampens with the square of the distance (which btw. is why I am puzzled that so few people use headsets for their cell phones), so just keep the routers et al. at at least twice the distance  of the TX/RX link inter-distance.

Also, I couldn't find a datasheet/manual for that link. Are you sure it would be viable for concurrent numbers up to I dunno, 20 max? Also, I didn't know they were that cheap. I thought they were closer to $40 per transmitter/receiver ($80 a set) that this changes things. Any other sites you'd recommend?

Manual is on the page.
22 pages:
http://www.hobbyking.com/hobbyking/store/uploads/1023035238X281904X57.pdf

73 pages:
http://www.hobbyking.com/hobbyking/store/uploads/1023035238X281904X26.pdf

You pair the transmitter and receiver with the included "bind plug" and then they're an item, as fiercely like two teenagers at the first week of their romance

No other sites to recommend, this is the cheapest 6 channel set I've seen.

I would assume we would host the event inside a school with the likes of bluetooth/802.11/etc rampant all around us. Specifically the Eng building of a major university. If that could cause an issue.

Just invite them over - might get you some local assistance now and then

Unless they use spark transmitters or heavily pulsed transmitters, you should be in the green regarding interference.