Wiring an On/Off Switch
 

Hello,

Yesterday I saw an all too familiar thing. A buddy of mine, also running an Schulze 18.97 speed control, plugged in and it just took off - full throttle. Then with cut up arms and fingers, he wrestled the deans out to shut it off. When a high voltage brushless runs away it's not fun. (in this case it was on the bench, but when it spins at full thottle it's scarry) Anyway, we don't know why his radio didn't seem to sync up, he was on the right model and everything worked fine when he tried it again but it makes me relize that we need an on/off switch.

How does one wire an on/off switch into the 18.97? My first thought was to put one in line with the BEC, the BEC uses small power wires and they must not carry much current. I'm sure that's a possible place for it but I wonder, if you split it there, does that force the Speedo not to power up? The speedo has a +/- which WILL have voltage, so will it arm even without a radio signal? My next thought was to somehow have a on/off in the power wires but I'd image given the high voltage and high amperage, that this isn't easy to do.

Any help on this would be greatly appreciated. There are 4 of us at our track who use 18.97's and none of us have any on/off.

Thanks,

DM

fit the switch to the bec , once you have connected the main wires the 18.97 will only give you the final arming bleep when the switch is turned on.

It 'sucking eggs' I know..................... but never power up you truck without the TX

What receiver/esc is he using? the Spektrum ghz set by coincidence?

A loose receiver pack would avoid this though.

another idea; make a little crossover on the plus pole with an extra plug on the Ubec, and connect it before you connect the speedo.. You can check if the signal is okay by steering left/right.

BUT..

Normally, when a 18.97 doesn't detects a receiver signal, it hit full brakes.. So my guess is that it may be some kind of interference as well.

I've seen it happen several times over the years. This particular time, he was using a Spektrum but I know I've seen it happen even with older stuff.

Another application/need is that when we line up, it would be nice to "turn off" the truck so it's not wasting juice waiting for the stragglers to get to the line but the BEC switch won't help that, fans will still be running and such... I think about my 1/10th stadium and how nice that on/off is...miss it.

It takes too long before the spektrum has connection, normally the Schulzehas got a startup delay, but apparently it wasn't 'slow' enough..

What was the Spektrum's failsafe programmed for? The throttle, steering, and AUX failsafe positions are programmed during the binding process.

Can't answer the Spektrum questions, they are a bit off the main subject of how best to wire in an On/Off, so far on the BEC is the only suggestion, any other ideas?

What i heard from Leroy, it isn't a failsafe, it just needs to connect. this takes some time, and the receiver just gives a WOT, again, i have got no personal experience with this, this is thought wisdom from an intense MSN session with Leroy.. (coolhand)

Same thing happened to me a while ago, its VERY scarey! A switch should help, i put one on and it works fine now!

My savage once went mental and had a unpleasant escape..

the result was a HUGE crash from a cliff.. It landed on it's back, it took me quite some time to help the poor thing out.. (it was a nasty climb) Luckely she was wearing protection.. (the beefy rolbar i made for her)

Both the truck and (then happy) owner survived this event without any further injury.

I think the Spektrum is at the heart of this problem.

As far as I know a switch on the BEC side is your only option, unless you can get some 100amp plus switches for the main power.....not very practical :002:
I too have had this problem ONLY with the 2.4ghz and stangley ONLY with the 9920 and not the 18.97. Fitting the switch to the BEC fixed the problem.

I too think the Spektrum is part of the problem, that's why I mentioned it. Binding position would be an easy thing to overlook and rectify. I always like to start with the easy (and free) solutions. Sorry to make it seem like I was going off on a tangeant. :)

A UBEC is a switching regulator and might be prone to start up noise until the regulator circuitry can settle down and provide relatively clean DC (switching regulators generally use current feedback to regulate the voltage). It is possible the Spektrum receiver does not like the startup noise and gets a little crazy. A switch is probably the easiest solution. Another may be to add a capacitor to the output of the BEC; it would filter the DC output and would also help beef up current pulses for better servo response.