UBEC installation

[babolimp]

Hi all

I find that my arrma outcast has a very wide turning circle on grass. I upgraded the servo mount to GKA and the servo to a savox 1210SG however I feel it still doesn't have enough torque on grass. The internal BEC gives the servo 6v which = 20kg of torque. I want to try it with an external UBEC, which will give it 7.4v and 32kg of torque.

I've never done this before, so I have a couple of questions

1. Is the UBEC I bought compatible with my setup? (arrma outcast 2018 + Savox 1210SG + Henge 12A UBEC)
2. looking at the attached image, is the wiring correct?

mods used:
servo (Savox 1210SG) = https://www.savoxusa.com/collection...ducts/savsw1210sg-waterproof-coreless-digital
servo mount (GKA) = https://www.gkacustomrcparts.com/product-page/cervo-mount
ubec (to be installed - Henge 12A UBEC) = https://www.ebay.com.au/itm/New-HEN...740585?hash=item1caeccc8a9:g:gTYAAOSwllpbFlNy

cheers

 

[2fast4u]

Is your servo saver adjusted correctly ? Dual rate on transmitter fully clockwise ? End points set ? That servo should be noticeably better than stock even at 6v.
On another note. The wiring configuration drawn on the picture is not correct if you ever intend to run two batteries in series. You have to connect the Bec + & - to the + & - of the ESC battery leads (As the wiring diagram shows)

 

[babolimp]

not 100% sure what a servo saver is, but i don't think i have one
dual rate is fully clockwise
end points are set to the point where they pull the servo mount just a bit at full turn
the servo is better than stock. stock was actually DOA and warranty replaced lol.
turning circles are just way too wide (at speed) unless i power slide

i don't intend to ever use 2 batteries in series
i just use one. i may as well use this opportunity to get rid of that extra XT90 connector seeing as i'll be resoldering anyway.
so it would end up with a connection like this. will that work?

 

[tjf]

That will work, don't cut the positive wire from esc, unpin from connector and insulate wire instead.

 

[2fast4u]

That will work, don't cut the positive wire from esc, unpin from connector and insulate wire instead.

Yes, that is correct. You are good without that second connector on the other ESC wire. You do in fact have a servo saver, your steering link from your servo horn is connected to it.

The top half of the saver is attached to the steering link, The bottom half is attached to the steering rack. The black nut at the bottom is the adjustment. You run it up to increase the pressure on the spring. If it is too loose it will turn fine with the wheels off the ground but when the car is on the ground it will open up when you turn, which decreases steering.

There is a hole in the chassis right next to the nut. You can insert an Allen wrench or small screwdriver just far enough to catch the nut and wedge it against it to hold it. Start by turning the wheels by hand fully to the right (looking at it as if you are sitting in the truck) Insert the tool to hold the nut, then turn the wheels fully left, release the tool and repeat until the adjustment is where you want it. Typically the nut ends up about 4-5mm above the chassis.

 

[babolimp]

thanks for the tip 2fast4u
it took me a while, but eventually i understood your instructions and tightened the servo saver

i visited my local hobby shop just to get some more advice.

they tightened the servo saver a lot more. apparently you can do this on a good servo as the gears can handle it. the servo saver is pretty loose on a stock setup because the stock servo gears are rubbish and will easily break under load. hell my stock servo broke during my 2nd run and i hadn't even touched the servo saver.

this car just needs a massive amount of torque in my opinion. the wheels are huge. hold onto the wheels and turn the steering wheel. you can feel how hard the servo has to work just to turn the wheels a little bit.

the UBEC isn't going to work unfortunately. the transmitter and receiver can't handle high voltage, it would just fry them. an expensive upgrade so i'm not keen. apparently you can run a separate 7.4v battery into the servo, which won't fry the rest of the system. sounds straight forward on paper at least, and would give me the torque i'm after. i might look into that.

 

[babolimp]

even though i'm a noob, i feel there's some good info i can provide to others. no one had mentioned it here and i could have easily stuffed up my car had i gone ahead.

as a rule of thumb, ready to run cars can only handle 6v. pumping a high voltage into them (via a high voltage BEC) will fry the electronics.

 

[tjf]

use the ubec with a y harness. 7.4 to the servo only, receiver powered by esc bec

 

[babolimp]

not following.

 

[tjf]

plug esc into port 2. remove power wire from y harness that plugs into receiver and insulate, plug the connector with ground and signal into port 1. ubec power and ground hooked into battery positive and negative. plug ubec output to 1 end of y harness plug servo into other end of y harness. 6v esc bec powering receiver, ubec powering servo, all grounds and signals connected.

 

[babolimp]

thank you for your advice tjf

i made a diagram - let me know if i got it right?

so in theory this setup will result in:

1. the external UBEC delivering 7.4v to servo only (servo can handle 7.4v) = high torque
2. the internal BEC delivering 6v to the receiver (receiver can only handle 6v)
3. no electronics going bust
4. everything else working as normal

just confirming the above is all true?

 

[tjf]

Yes, diagram is correct and esc bec will supply 6v to receiver and ubec will supply set voltage (7.4) directly to servo. I have many rock crawlers wired this way using Castle Creations external becs.

 

[babolimp]

it worked! steering torque was noticeably stronger. however there was less power to the motor compared to before. i guess i should have expected that going from 3A 6v (stock bec) to 3A 6v (stock bec)+ 12A 7.4v (external bec)

i also tried it with a separate 3S battery powering the BEC, which resulted in full power to both the motor and servo. i couldn't really find space for the battery though.

the other issue with both configs was that the BEC turns on as soon as you plug in the battery. the stock on/off switch doesn't apply to the external BEC. just something to keep in mind because you need to open the hood to unplug/plug the battery every time you want to use the car. a bit annoying.

in the end i reverted back to the setup i had before. power to the motor trumps servo torque for me, plus the battery thing is an annoyance.

 

[tjf]

You shouldn't have less motor power. The bec does not supply 12A constantly, only the current that is demanded from it which is only one servo. As for the switch, on all my castle esc's, I have the switches removed anyway. Also, you should always unplug batteries because the switch technically only shuts off the bec and not the esc. With the switch off and receiver powered up separately, you would be able to drive the car.

 

[tjf]

Not unplugging battery can cause batteries to drain fully or to unrecoverable low voltage levels.

 

[DoNoHarm]

Yeah it ain’t smart to leave packs plugged in with the car off at all.. I normally leave the switch on all the time to avoid any issues. I’ve had a few esc’s in my time wear out and become a dead short if the power was off. When you turned it on, the LED would become a resistor and all would be well, but if you already had it off say goodnight to your battery. I just don’t like the fact of plugging batteries into something not drawing power after my experiences.

 

[crimsonfancy]

Yeah it ain’t smart to leave packs plugged in with the car off at all.. I normally leave the switch on all the time to avoid any issues. I’ve had a few esc’s in my time wear out and become a dead short if the power was off. When you turned it on, the LED would become a resistor and all would be well, but if you already had it off say goodnight to your battery. I just don’t like the fact of plugging batteries into something not drawing power after my experiences.

Key tip. Good idea just leaving the toggle on and easier to remember to unplug at least.