Failsafe makes car go mad

[Buggington]

Hi all!

Just bought a BSD Racing Defender and I bought all the essentials - crystals, fuel, after run oil, air filter oil and a failsafe.

I fitted the failsafe to the car and drove it around a cricket pitch for a while. As I drove it further away it started going mad, as though it was out of range.

I stopped, killed the engine and disconnected the failsafe. From then on it worked fine. Any ideas why this could be?

Buggington

 

[Metalhead Matt]

If you don't have a good nimh rx hump pack, the failsafe may not be getting the proper amount of voltage. But it should not go mad, it should only do what you set it up to do. I would try the hump pack and setup the f.s. again.

 

[Buggington]

Right, I understand the part about voltage but what is a hump pack?

 

[Racer 1966]

He just means a rechargeable pack. The hump refers to the cells being stacked on each other. You'll have to see what fits your battery box.

 

[Buggington]

Good idea - it's a set of 4 rechargable AAs in there. I charged them recently - will do so again soon.

Thanks

Buggington

 

[Amoeba]

I'd second the recommendation to get a NiMH hump or stick pack. AA's have a much weaker burst C rating and tend to dip below the sustained C output easily which can lead to all kinds of weirdness. The NiMH rechargable packs are much better in that regard.

**Edit: olds put what I was saying into more detailed terms below.

 

[olds97_lss]

Good idea - it's a set of 4 rechargable AAs in there.

More than likely, this is your problem. Rechargeable AA cells only put out 1.2V per cell. Many fail safe's kick in when the voltage drops below 4.1V or so. With the receiver drawing power and the servos drawing power, it takes very little time and effort to take 4.8V and drop it down to 4V.

"hump" packs and general rechargeable receiver packs are 5 cells that put out 1.2V per cell which adds up to a 6V pack.

Alkalines are generally not used at all, but 4 of them puts out 6 volts since each cell puts out 1.5V. However, they are quick to drop voltage and current due to their chemical make up. In a high drain situation (servos, especially on the brakes or digital servos), alkalines won't last very long and they won't give you peak performance out of your servos.

Basically, get yourself a 6V RC receiver pack and hopefully that will cure your issues and let your run a fail safe.

For my needs, I made 5 cell AA packs out of 2100Mah NiMH AA cells. Took some solder, tape, hot glue and wire, but works really well and I don't notice much if any performance loss when comparing to a 2/3A (typical RC receiver cells) pack. The 2/3A cells are fatter and have larger platters which allows for higher/faster current drain. This is good for mini vehicles or if your running all digital servos. For what I do though, the AA rechargeable cells work fine.

 

[Buggington]

Great, thanks.

And running at 6v won't kill everything will it?

Buggington

P.S. Sorry about all the extra questions - I'm a noob when it comes to this stuff

 

[Amoeba]

Great, thanks.

And running at 6v won't kill everything will it?

Buggington

P.S. Sorry about all the extra questions - I'm a noob when it comes to this stuff

Nope, they're designed for 6V.

And noob questions are what we're here for!

 

[olds97_lss]

Nope, they're designed for 6V.

And noob questions are what we're here for!

+1 on both!

4 alkalines put out 6V.
5 NiMH cells put out 6V.

Going over 7V or so generally is a bad idea unless your equipment is made for it. Most receivers/servos work with 4.8-6.8, but generally work better when your floating at at least 6V constant.

 

[Buggington]

Is this the kind of thing I need?

http://www.modelsport.co.uk/?CallFunction=ShowSpecification&ItemID=24135

 

[Amoeba]

Yup, that's a 5-cell hump pack. If you can, go with a 1600mAh pack, especially if you are running high-torque digital servos. You'll get much longer run times between charges. The higher the mAh the more capacity of the pack.

 

[revo_rob_1984]

P.S. Sorry about all the extra questions - I'm a noob when it comes to this stuff

hey at least ur asking questions and going with the suggestions unlike some people on here but then act like they know everthing*cough*TMAXX96*cough, cough*QUARRT*cough* sorry about that i must have had a tickle in my throat lol