Power Issues

Hi All,

We recently got to the stage of having a rolling chassis, so fired it up to find the robot incredibly sluggish, so much so that powering both motors simultaneously brought the robot to a stop!

We have 2 12v drill motors, 2 15amp electronize ESC (2nd hand) and 2 Ni-cad battery packs 8.4v each (7 cells) when charged holding about 9.5v wired in series.

The ESC arn't quite right, the BEC's are out putting the full 18v, and despite taking them apart I can't see why. While running the robot I measured the voltages are certain stages. From the batteries its at the full 18v, but the motors are only getting 5v, tops!

The ESC are turned all the way up on the speed control and the wiring is sound.

The cells are those from the drills we got the motors, so they-re are not the best, but this seems like an extreme voltage drop. Anyone got any ideas as to what is going on?

I'm going to try it in the next few days with some Ni-mh hobby packs we have to see if that makes a difference and eliminate whether it is the ESC that are playing up or the batteries.

On a final note anyone got a good source where you can by ni-mh cells from? I can't find any.

Thanks!

I (and several others) get ni-mh battery packs from Vapextech, through their eBay shop:

http://stores.ebay.co.uk/vapextechbatteriesandchargers

They're pretty cheap and very good quality.

As for the power issue, not 100% sure on that but all I can suggest is take it apart and wire up each motor/esc/battery separately as a test-bed and use a receiver with an external battery (this will indicate if the bec is the problem). What speed controller are you using again?

Would it not be cheaper to buy a ready made pack/s? there's loads on ebay ranging from cheap and cheerful all the way up to the more expensive packs.


EDIT: beaten to it

BEC's are out putting the full 18v!!!!!!!!!!!!!!!!!

very odd

should be 5v from the BEC's

18v for the motors.

9.5v wired in series...typo? ...19.5v in series?

They are the Electronize FR15HVR models I think (don't have them in front of me right now) The 15amp ones with BEC's.

I'll check that shop out.

Wiring seems pretty sound, but Ill try one ESC at a time.

Any ideas about the BEC not working?

Yeh so it looks like the BEC and motors have been swapped, only the motors still retain the voltage control..... On both!

I have emailed the guy I bought them from to see if he knows whats going on, I received them like this.

BEC or BEC's ?

Use only ONE never both.

Hhmmm ..Should make this post clearer

If your controllers each have a Battery Eliminator Circuit you must only connect ONE BEC not both.

Both ESC's have a BEC, but only one of them is connected to the Receiver, on the other i have insulated the ends of the BEC wires.

Sort of a typo, the over volting in the packs doesn't stick around long, they soon drop to 18v

Any chance of a wiring sketch and or pic of the assembly?

Just on the off chance that you may have made a wiring error.

[attachment=0:1wa07zn9]bat%20motor%20controller2.JPG[/attachment:1wa07zn9]

stupid question time, to activate the BEC, you are just soldering together the red and orange wire and then insulating? If i remember right, the voltage between these wires should be 18v.

The 18v you measure, is that from the red and black wires on the servo plug that goes into the receiver?