Failsafe mechanisms

Simon Windisch · Post by **Simon Windisch** » Sat Jul 02, 2005 7:42 pm

Hi there,

I'm using a new SOZBOTS - MX Speed Controller http://www.sozbots.com/stores/popups/SOZDSCR2.htm and am horrified to learn that it does not fail safe if the transmitter turns off.

Has anyone else had experience of this?

Simon

Andrew_Hibberd · Post by **Andrew_Hibberd** » Sun Jul 03, 2005 3:05 pm

I am not aware that anyone else who uses the MX board, i have never had a problem with the dual motor boards. What did it do when the tx was off?

Simon Windisch · Post by **Simon Windisch** » Sun Jul 03, 2005 10:03 pm

When I plugged the battery into the robot it just raced away with the transmitter turned off. If I turn the transmitter on for a few seconds and then turn it off again then the robot fails safe, most of the time. But it's not very good.

Simon

Andrew_Hibberd · Post by **Andrew_Hibberd** » Mon Jul 04, 2005 9:57 am

Sounds very odd, you could try and turn the tx on before the robot to avoid the stuff at the start. Have you tried speaking with sozbots?

Adam Hargreaves · Post by **Adam Hargreaves** » Mon Jul 04, 2005 12:38 pm

I have a big fat warning sticker on my Tx, which warns me to always turn it on first, adn the Rx afterwards...

Remote-Controlled Dave · Mon Jul 04, 2005 3:56 pm

I've always pretty much ignored that and mine are all fine...

Simon Windisch · Post by **Simon Windisch** » Mon Jul 04, 2005 5:08 pm

Yes, I have contacted Sozbots. Still no reply, still I think that today is a holiday for them.

I believe that if you're using servos then they fail safe automatically.

Simon

Post by **BeligerAnt** » Mon Jul 04, 2005 8:53 pm

Simon, I assume you've read the manual?

Does the board behave like the manual says it should? It infers (but doesn't explicitly state) that there is some sort of failsafe.
Is your receiver well-behaved? The manual mentions "glitchy" receivers. How does your rx behave with standard servos connected? Is it picking up interference from your PC/mobile phone/etc?
Are all your motors suppressed with ceramic capacitors right across the motor terminals?

Standard servos only have a kind of simple "accidental" failsafe, in that they will generally try to hold position (i.e. stop) in the absence of any data. Noise picked up by a receiver is often interpreted as data and servos will misbehave.
Speed controllers on the other hand usually have a much more sophisticated failsafe mechanism. At power-on they usually wait for a valid "neutral" pulse (or several) before enabling the motor drive circuit. The chances of getting a string of 1.5ms pulses out of the receiver as a result of random interference are slim so the failsafe is quite effective.

To help the support guys diagnose/fix your problem, give them as much information as possible. What is the exact setup? What is the exact sequence of events? What does the LED do? How do the motors run? (Full speed, slowly, steady, erratically, etc) Is the behaviour repeatable? Have you tried different configurations? (Different receiver, crystal, motors etc)

Simon Windisch · Post by **Simon Windisch** » Tue Jul 05, 2005 10:31 pm

OK, thanks Gary. I need to do some heavy work before AWS 17 then.

Simon