Power Problem running Sabertooth and Servo.

[Shakey]

Hi I am relatively new to antweights and going along to Robot Rumble yesterday inspired me to get some more work done on mine. However there is a problem.

The current set up is:
Sabertooth 2x5 RC Motor Controller
2x motors (not exactly sure on the make/model)
Spektrum AR6100e + DX6i 2.4 GHz
350mAh 7.4V 2 cell LiPo

That runs perfectly fine however when I attempt to use a servo in conjunction with it ( By plugging it into the appropriate receiver socket, in this case throttle) the system doesn't receive enough power meaning the sabertooth and the servo are resetting constantly leading to continous uncontrolled movement in the mototrs and servo.

I can't remember the exact name of the person but I briefly spoke to him at the event and he reffered me to here. Also I understand the 1/3 metal armour and 1mm metal armour rule is gone?

I am unsure how to fix this problem so any help is appreciated.

[peterwaller]

This is a problem several people have experienced especially when using a high power servo like the Park HPX F. The problem is that the controller has a BEC (battery elimination circuit) that supplies 5 volt power to the reciever. This is designed for running a reciever or micro controller which draw a few mA but is not up to running a servo like the HPX F that can draw around 1.5A peak. This causes the 5V supply to dip well below the 3.5V that is required by the receiver and that causes the problem. Here is a waveform showing the effect of an HPX F servo on a 1A regulator.
The red trace is the battery voltage and the blue one is the 5 volt regulated output which can be seen to drop to about 2V for a brief period.
http://i109.photobucket.com/albums/n66/ ... SRHPXF.jpg
The only way round this is to add a second regulator (see Simons site for details) to power the servo or power the servo direct from the battery (assuming only a 2 cell pack) but this is overunning the servo quite a lot and although many people do opt for this I don't really recommend it.

[Shakey]

I will probably have to build a new regulator as a month ago I was playing around with the circuits and accidentally ran the 8.4V from the fully charged 2 cell through a HPX blowing something.

Thankyou for the advice, I hope to have this antweight up and running for an event soon. Also in the works is a planned featherweight flipper.

[Simon Windisch]

Good luck Haywire. BTW how did you get into antweights?

Simon

[Shakey]

Good luck Haywire. BTW how did you get into antweights?

Simon

I think it was a mix of robot wars loving and Not having enough to make a big robot. Though me and my friend (both 15) are making featherweights soon.

Do any of you know what it would be like running another motor controler (to make 3 motors) as well as the sabertooth or would the problem persist/be worse?

[Simon Windisch]

Fast Dalek uses a Sabretooth for the wheels and a scorpion minifor the lifter.

It's not the greatest design however: the motor doesn't stop at the end of its travel like a sevo would, and the gears are always breaking.

Simon

[Shakey]

Fast Dalek uses a Sabretooth for the wheels and a scorpion minifor the lifter.

It's not the greatest design however: the motor doesn't stop at the end of its travel like a sevo would, and the gears are always breaking.

Simon

My planned weapon is a vertical fly wheel to chuck robots away and possibly damage so not stopping suddenly shouldn't be a problem as that would damage any motor. The potential problem would be if it takes to long to slow down. there might be a possible setting on the DX6i. It woiuld be on the throttle channel so as to return to a preset position 9off) when radio contct is lost and so it doesn't keep powering up and down while the stick springs back if I accidentally let go.

[Simon Windisch]

OK, I think you'll need a speed controller like model aeroplanes have. I don't know much about those...

Simon

[joey_picus]

I don't think the flywheel taking too long to slow down would be an issue, as long as you're removing all power to the disc motor when the robot failsafes or turns off it doesn't matter if it takes a while for the weapon to stop, usually the lid will be held down during that time (as with Peter's spinners) to protect people if something does go wrong.

As Simon says though you will definitely need a small single channel speed controller for the weapon rather than any sort of servo setup - having a servo pushing/pulling a switch is far from ideal because they can't be relied on to failsafe properly.

[Shakey]

I don't think the flywheel taking too long to slow down would be an issue, as long as you're removing all power to the disc motor when the robot failsafes or turns off it doesn't matter if it takes a while for the weapon to stop, usually the lid will be held down during that time (as with Peter's spinners) to protect people if something does go wrong.

As Simon says though you will definitely need a small single channel speed controller for the weapon rather than any sort of servo setup - having a servo pushing/pulling a switch is far from ideal because they can't be relied on to failsafe properly.

The servo question was because I was looking into a flipper aswell but decided to go for a bit more exciting wepaonry.

Also that sounds good then.