Controlling bots with bluetooth

**muchalucha** · 25th August 2009, 20:41

I have wanted to switch to 2.4 ghz for a while, spektrum stuff is too expensive for me so ive been looking into bluetooth control, i want to use a 100 M bluetooth dongle with my laptop and a usb game pad or joystick or something for the controls , and a for the Rx , a serial to bluetooth adapter , an arduino and a custom made pcb to interface up to eight servos with the arduino. Bluetooth is spread-spectrum , like spektrum radio's so as far as i know there shouldn't be any problesm , but the FRA rules dont actually say that bluetooth is allowed , so does anybody in the know , know if bluetooth is ok, and if my plan is doomed to fail ?

any help would be good

**leorcc** · 26th August 2009, 08:34

Bluetooth is 2.4GHz and digital and therefore covered in the rules and regulations. However, you will have to demonstrate that the failsafing works and that your implementation doesn't interfere with other systems on the band (which is very unlikely).

**muchalucha** · 26th August 2009, 09:41

I was going to do failsafing in the software , will that be ok do ya think? Im pretty sure the failsafes in my esc's wont work with this as i cant directly emulate an RX , just tell a servo to go to certain position

**leorcc** · 26th August 2009, 09:52

That's what spektrum does as well in their receivers (except the AR500) that is why failsafes are useless in Spektrum driven robots.

**muchalucha** · 26th August 2009, 10:29

bcause the receiver has a brain im hoping that , as it wont know if its lost connection , it will just stop working , it will just give no instructions to the esc's , at which point the failsafes in the esc will kick in , im thinking of bypassing the whole analog to digital to analog again thing and just feeding the raw data straight into the esc that way there would be no need for any failsafes and it would be a lot safer

**big_nipper** · 26th August 2009, 12:03

Failsafes, mean for a robot point of view that it must come to a controlled stop when loss of radio signal is detected. This also applies to any weapons in that they must not activate unintentionally. It does not matter how you implement this as long as it works and can be demonstrated during tech check. From your point of view this could be demonstrated by unpluging the bluetooth adaptor from your laptop while driving/turning at full speed. If it then stops all is well.

I would also check that Bluetooth is allowed for remote control (though I cant see why it wouldn't be). I know that 433MHz tranceivers that are very cheap (<Â£10) seem a good idea but regulation don't allow for control but just telemetry of data as I looked at this a while back for another project.

I would still recommend you look at a Spectrum system, they are really not that expensive (dx5), espacally if you take into account of the 2 bluetooth modules and the joystick you need, unless you have a cheaper source than me.

**Metal Demons** · 26th August 2009, 12:52

That's way, way more effort than just getting a Spektrum dx5e or whatever off ebay.

**leorcc** · 26th August 2009, 13:45

I agree it is a lot of hassle and I'd rather buy a DX5 as well, but the question was whether it is allowed or not. I opened up the build rules to make sure before I answered and I see nothing in those rules that would exclude Bluetooth.

**geoff** · 26th August 2009, 15:12

I agree with Leo, there is nothing in the build rules that excludes the use of bluetooth as a control medium. However, you will be required to demonstrate it's ability to comply with section 4.2 of the build rules.....

4.2.1.
All systems that are deemed to be 'dangerous' (normally the drive and weapons)
must have a 'failsafe' device. This MUST bring the systems to a pre-set 'off' or 'zero'
position if the transmitter signal experiences interference or is lost. These devices
should also failsafe when the receiver battery is low or if power is completely lost.
4.2.2.
The failsafe(s) may take the form of plug-in commercial devices; electronic circuitry
incorporated into some receivers e.g. PCM type; or other devices e.g. electronic
speed controllers such as the Vantec. It could also consist of digital switches, which
return to preset off position on loss of power. Care should be taken in the selection of
devices to ensure they meet the requirements specified above.

Providing your bluetooth set-up can comply with the above then I see no problem with your plans.

Geoff Smith
FRA acting safety officer.