Sabertooth servo problem

[X3T]

I'm using a Sabertooth 5A speed controller, connected to a Lemon-RX receiver. I have a single servo connected to the receiver, and am using a 6V NiMH battery. When activating the servo the Sabertooth cuts out and resets. I have read that there is a weak BEC on the Sabertooth so I connected the servo directly to the battery, but still have exactly the same issue. A friend suggested I put a capacitor in but again this made zero difference. I have tried 3 different servos, including a cheap low power one. My first ant is pretty useless at the moment!

[peterwaller]

First welcome to the forum.
The sabertooth controllers have always been susceptible to low voltage operation.
Although they quote 6 to 18 v operation they also say 6 to 12 NiMh cells which is 7.2V min.
I would think your best bet is to use either an extra cell or change to 2 Lipo cells.
Good luck with your first antweight.

[X3T]

Thanks!

Yeah I suspected the battery but didn't want to believe it as the battery only just fits with 5 cells . I did look for 6 cell packs but couldn't find any (currently using 120mah which lasts ages). I am wary about going with lithium batteries for now as robot building is new to me.

I'll see if I can move things around and locate a 6 cell pack.

[AntRoboteer]

I've had many servo issues with those 120mAh batteries when you use a high power servo such as a Park HPX F. The reason for me was that the battery could not supply enough current to drive the main servo. This was not just because the battery was powering a huge speed controller (I was even using servo drive on that one ) but because those batteries just cannot supply the sort of current required for such a servo.This was tested using 3 batteries, all 5 cell, all 120mAh and all showed the same symptoms.

The solution I came across was to pick up a 210mAh pack which seems to drive the servo in question just fine. Not sure if that would work for you but if you did have a higher capacity one lying about, you could give it a go.

Hope that's helped a bit and best of luck for the antweight; I can't wait to see it!

[X3T]

Ah ok, thanks. I don't have a spare but I'll order one, worth a try! How much do the 210mah packs weigh?

[peterwaller]

I don't know exactly which battery you are using but I found a 120 mah on ebay and they are only rated at 0.5A max discharge where some servo's can take upto 1.5 A.
http://www.ebay.co.uk/itm/Micro-6V-RX-1 ... 3641.l6368
If you change to LiPo you can get a 180 mah from hobbyking which is 25C rating or 4.5A
http://www.hobbyking.com/hobbyking/stor ... duct=34369
NiMh 18 gms 51 x 15 x 10.5mm 120 mah and 0.5A discharge
LiPo 13 gms 35 x 20 x 10mm 180 mah and 4.5A discharge
You will need a proper LiPo charger but you can see why almost everyone has switched to LiPo's

[Remote-Controlled Dave]

I always had problems getting a sabretooth and a weapon servo to run simultaneously no matter what components I used. There's just something about them. Best I ever got was one that would work on full charge for about a minute before everything failed. So I just gave up. I'm sure its possible I just found it too problematic to bother.

[AntRoboteer]

It's one of these that I'm talking about:
http://www.componentshop.co.uk/6v-1-2aa ... -pack.html

That weighs about 30g and is rather large so consider placement carefully if you do decide to go with one. The dimensions are on one of the pictures on the listing. They are fantastic batteries though; good enough to power my Baby Orangutan board (taking care of the drive), receiver and LED matrix (controlled by a second board) altogether quite easily as well as being able to handle a large servo with ease.

[X3T]

Thanks for all the replies.

Wow I didn't realise how much better LiPo batteries are! Crazy cheap too. Yes that first link is the battery I have. What is the risk with LiPos, i.e. how likely are they to go up in a fireball? I've got to wonder when they sell special fire containment bags to charge them in.

Yeh I have just bought that 210mah pack along with a 6 cell 120mah, just so I can test them out and see whether it's the current or the voltage which is the issue here. Probably will go with a LiPo for my next robot anyway.

[Shakey]

LiPo's only really fireball if they are overcharged and then suffer damage on top of that. All LiPo charges won't allow one to be overcharged. I've never actually been able to get one to properly fireball despite the fact I've overcharged and hit them with my feather axe before!

LiPo bags are still a good idea though. And they are far far better. A 2cell 180mah Turnigy nanotech LiPo is my preferred choice.