BEC necessary with upgraded servo(s)?

[StomperCrawler]

Some here are recommending adding a BEC to the stock ESC in order to:

1. protect it from the higher current draw of more powerful servos
2. provide more amperage to the higher-torque servos

What's y'all's experience been?

1. Is a BEC really necessary? If so, what amperage @ 6v?
2. What are the chances of one or two 16kg servos frying the ESC?
3. Can the ESC put out enough amps to power one 16kg servo? Two?
4. Will Redcat stand behind its ESC when used for aftermarket servos?

 

[d_j_stockton]

See this thread. http://www.rccrawler.com/forum/chit-chat-classics/211365-yes-you-need-external-bec.html or explains a lot.

 

[Frankenwheely]

See this thread. http://www.rccrawler.com/forum/chit-chat-classics/211365-yes-you-need-external-bec.html or explains a lot.

X100!:twisted:

 

[AutoCrawler]

I read most of that thread and its very long and silly and not very helpful.

The stock RS10 ESC BEC is rated at 5A (10A) peak. This should be plenty to drive two 15g servos in normal use. I have one 15 an one stock 6 and not problems so far. Although its a consideration, its not really the servo torque that is the problem by how often you stall your servos and motors since stalls draw a lot of current. If your driving style involves stalling the steering and the motors a lot then an external BEC may be worthwhile for you but if you are just adding one to insure the ESC in case, it may not be worth the cost. Redcat have a lifetime replacement on electronics for a nominal fee and and the max cost for a new ESC under that program is $35 assuming they judge misuse. (Warranty) which ia about the price of a 10A BEC. So it probably makes sense to just add the servos you want and see how it goes. If you think they are causing the stock ESC BEC to overheat then swap the stocks servos back temporarily and order a 10A BEC. Or just wait till the ESC burns out and replace it with a better one.

 

[StomperCrawler]

The stock RS10 ESC BEC is rated at 5A (10A) peak. This should be plenty to drive two 15g servos in normal use.. Although its a consideration, its not really the servo torque that is the problem by how often you stall your servos and motors since stalls draw a lot of current. If your driving style involves stalling the steering and the motors a lot then an external BEC may be worthwhile for you but if you are just adding one to insure the ESC in case, it may not be worth the cost.

Wow AutoCrawler, it sounds like you really know your stuff! Thanks for saving me from more than just scanning those 6 pages of back & forth arguments.

Redcat have a lifetime replacement on electronics for a nominal fee and and the max cost for a new ESC under that program is $35 assuming they judge misuse. (Warranty) which ia about the price of a 10A BEC. So it probably makes sense to just add the servos you want and see how it goes. If you think they are causing the stock ESC BEC to overheat then swap the stocks servos back temporarily and order a 10A BEC. Or just wait till the ESC burns out and replace it with a better one.

How much is the nominal fee and when do I pay it? How long does it for replacement parts to come? Do I have to send in the bad part first and have them evaluate it, or can they do a hot-swap where the packages pass in the night and they use my credit card as security?

Sorry for all the questions.

 

[d_j_stockton]

yeah the esc might put out 5A but it will only be doing it at 5v ish, i know that mine had 5.1v at the rx but when checked with a multimeter it was down to 4.7v at the servo.

most servo's when you look at their specs have more than 1 torque rating, take my old 12kg servo, it was 9kg at 4.8v - 10kg at 5v and 12 kg at 7.2v

so what im saying is yes the stock esc has the ability to power 2 x 12kg servos This was my setup before i gotride of rear steer) but because the were only getting 4.8v from the internal bec, were only outputting 9kg.

i have since got an external bec (just a cheap one for now before i can get a castle creations bec) and set it to 6v and it makes a huge difference to the steering speed and power.

the best way to see this i found was to find a friend who has one and plug your servo (still mounted on your truck) into their bec and get them to swing the steering back and forth. (i did this and it was the main convicing fator for mee to get one)

its not just torque that will improve it is also speed.

with my bec on when im in a steering bind i can actuall move the whole truck sideways by turning the steering into the obstruction.

i attend social comps and what i see just about everyone doing is shaking the steering side to side to reposition the truck without the need to reverse off an obsticle, bearing in mind it is the added torque and speed of the bec that makes this possible. i just dont think it could be done without, atleast now as easy as i can do it now.

 

[StomperCrawler]

DJ, are you using the stock ESC and RX? I thought that if you plug more than 5v of BEC power into the RX it would fry it?!? :shock:

 

[jsowens]

If you guys are happy not having a BEC...don't install one. Simple as that. I run one with no issues on my truck and have ran it for a couple of years now. You don't really see people posting on here saying that their BEC fried their ESC. A BEC routes more power to a servo, resulting in more torque and speed. I'm scratching my head wondering how that's a bad thing.

 

[StomperCrawler]

If you guys are happy not having a BEC...don't install one. Simple as that. I run one with no issues on my truck and have ran it for a couple of years now. You don't really see people posting on here saying that their BEC fried their ESC. A BEC routes more power to a servo, resulting in more torque and speed. I'm scratching my head wondering how that's a bad thing.

That's true, I haven't seen anyone around here saying that... and I've done quite a bit of reading so that this is how my eyes look now: :shock:

Seriously though, I guess I'll shoot for a 6v 5a and see how it goes. Thanks JS for setting me straight.

 

[AutoCrawler]

I don't have any personal experience wit the Redcat Warranty. Only what they promise on their site and that so far I have only read good things on the boards. I posted the link to main page above so you should be able to answer your questions there.

Don't think anyone is suggesting an external BEC is a bad thing. Just that it cost money and it may not be necessary depending on what you want.

Running at 6v will certainly give you more servo torque but may put strain on the RX. The redcat RX operating voltage is not specified as far as I've found. We only know that it ships running at 5v so its unclear if it's safe to run it at 6v It will almost certainly work for a while. The problem is that running electronics out of spec is a crap shoot. It will work fine for 8 out of 10 people but you might have a marginal part and it will fail for you. No problem if you have the money to replace it. That said this is not a mission to mars so if others say it works well and you like the advantages they claim then it may be worth a shot. If you fry the RX then you can use that as an excuse to buy a whole new TX/RX radio setup which you probably want.

If you want to play it safe and you are cheap then it's not clear to me that and external 5v BEC with the stock ESC will provide much additional advantage above just changing the servos from 6g to 15g. It really depends on how close to spec the stock internal BEC is. I haven't measured anything yet so it's a guess. On the other hand an external BEC can be had for less than $10 so why not just try it. Just remember to disconnect the power wire (RED wire usually) from the internal BEC that goes to the RX or it will fight with the external BEC an that won't be good. You need to leave the common and signal wires so the RX can still control the ESC.

With a part like this...

Turnigy 5V/6V 5A Heli-UBEC for Lipoly (6~16V)

you can switch between 5 and 6v easily so you can experiment. This is just an example not a recommendation. I haven't tried or researched this part. It may not work well with NiMH batteries although 7.4v is well in spec.

 

[AutoCrawler]

so I got my multimeter working. it had a bad battery so I stole one out of the smoke alarm - remind me to put it back

so I have the 15g metal gear servo that Crawford Precision Engineering sell (CPE-SER4). I found the spec sheet and its is actually meant for engine powered models and is spec'ed at 6v 14g to 7.2v 15g

The company that makes this servo says of itelf, "Now our servo production technology is on the rise by constantly absorbing the advanced technology and guiding from the expert." and "“Quality First, Business Trustworthy” is our constant goal," so its got to be good.

I measured the voltage at the receiver and its is 5.02v. Turning the only the front wheels using this servo full lock the voltage drops to 4.98 v. Laying the Rs10 on its side the front steering will lift the front up on the edge of the tire as far as it will go with no problem. The drop of 0.04v means it is stressing the internal BEC a little and two of these servos will stress it a little more. I don't have 2 to test to see how much but a .04v drop doesn't seem that significant for something that is typically momentary. It would be interesting to measure the current draw but I would need to make a little tool do that and I'm not sure this multi-meter is up to it.

Turning only the back wheels full lock with the stock servo I see little or no voltage drop (maybe sometimes 0.01) and turning it on its side the edge of the tire only barely and slowly lifts off the ground.

I also tried the pushing sideways test against an immovable object on a hard wood floor. The stock servo barely moves the truck sideways. The 15g servo smartly pushes it to the side.

I don't have an external BEC to play with so we can't say anything conclusive about using an external BEC from this experiment except that while a 5v one won't hurt anything and does provide you with some insurance you almost certainly don't need one just to upgrade one servo.

 

[StomperCrawler]

Thanks for the thorough response AutoCrawler, and please DO PUT THE BATTERY BACK IN YOUR SMOKE DETECTOR!!! I'd hate to have something bad happen as a result of your helping me figure this out. I think I'll go with a 6v/5a UBEC which as I understand it, doesn't try to run the power through the RX for the servo, but rather simply powers both it (the RX) as well as the servo(s); and yes I'll remember to cut the red wire from between the servo(s) and the RX.

 

[AutoCrawler]

Thanks for the thorough response AutoCrawler, and please DO PUT THE BATTERY BACK IN YOUR SMOKE DETECTOR!!! I'd hate to have something bad happen as a result of your helping me figure this out. I think I'll go with a 6v/5a UBEC which as I understand it, doesn't try to run the power through the RX for the servo, but rather simply powers both it (the RX) as well as the servo(s); and yes I'll remember to cut the red wire from between the servo(s) and the RX.

Thanks for the reminder. I just put the battery back in the smoke alarm. Might not have done if you hadn't reminded me

I guess I don't know how that would work. Do you have specific part it mind? I'm wondering how it gets wired in? Don't want to flog a dead horse if we are done here but I'm curious.

 

[StomperCrawler]

Do you have specific part it mind? I'm wondering how it gets wired in?

Something like this running at 6v for servo speed/torque and wired like this:

 

[AutoCrawler]

Thanks for the photo. I'm not sure if I can make out what's going on there. What BEC is that?

Looks like the RX is controlling the Servo via CH1 assuming the Black is -ve and the Yellow is the signal and assuming the Brown/Red/Orange PCM cable is going to the servo. The servo is getting its +ve directly from the external BEC

From the wires in channel 2 it looks like maybe the RX powered from the ESC internal BEC via the red wire and is controlling the ESC via the White wire.

That arrangement makes sense on the redcat too since it means the RX still gets the 5v it wants from the internal BEC on the ESC but you are powering the Servo from the external BEC with 6v. One concern is whether the signal from the RX will control the servo properly since it can only swing 5v but so long as the signal voltage crosses the servo switching threshold it should work. Another concern is whether the servo will pull up the signal line to 6v when it is switched causing problems for the RX but my guess is that they thought of that and the signal pulls down to ground.

So if I've interpreted your picture correctly and assuming my two concerns don't apply, I'm convinced that would be a safe way to give your servo(s) a higher voltage. Basically you are using two BECs to provide two different voltages.

Which leads me to speculate that since my CPE-SER4 servo is rated at 6 to 7.2v I could power it direct from the NIMH battery using this technique to get the full 15g torque and full speed with just some wiring changes. Interesting... Something to try this weekend.

 

[StomperCrawler]

So if I've interpreted your picture correctly and assuming my two concerns don't apply, I'm convinced that would be a safe way to give your servo(s) a higher voltage. Basically you are using two BECs to provide two different voltages.

If it doesn't work then I'll just swap the external BEC over to 5v mode. ;-)

Which leads me to speculate that since my CPE-SER4 servo is rated at 6 to 7.2v I could power it direct from the NIMH battery using this technique to get the full 15g torque and full speed with just some wiring changes. Interesting... Something to try this weekend.

I've read about people doing this and it seems to work well. "thumbsup"

 

[AutoCrawler]

Found this thread which is interesting

http://www.rccrawler.com/forum/redcat-rs10/238533-esc-voltage-question.html

Seems the stock ESC may be underrated and may work fine at higher voltages...hmm will have to investigate further. It makes sense that the internal BEC would not work as well at higher voltage. The higher the input voltage the more work the BEC has to do to maintain its 5v output and therefore the less current (amps) it can supply before it overheats. Essentially the BEC converts the higher voltage to a lower voltage by dissipating the unwanted voltage as heat. More voltage = more heat to get the same current.

One thing did occur to me though... Why don't people put in-line fuses in these circuits? Seems to me it would save a lot of burn outs. It makes sense to me to protect the circuit with a 20 c fuse rather than using the $50 ESC or $20 Servo or even a $6 BEC as a fuse. There are even small thermal breakers you can get if you want to be a bit more sophisticated....hmm have to investigate that further too.

 

[IQLogic]

I'm using THIS as a BEC "thumbsup"

300kHz - Adjustable voltage - max 12A - $8.98

 

[AutoCrawler]

I'm using THIS as a BEC "thumbsup"
300kHz - Adjustable voltage - max 12A - $8.98

:shock: You don't mess around...

 

[Meatwad]

That thing is monstrous compared to a ccbec! Where do you have that mounted?

In my experiences, when running 2s packs a bec is less required as far as function. BUT, using a bec does make the servos function more efficient and stronger regardless of pack voltage. When running 3s packs, alot of internal bec's can't handle kicking down more than half the voltage and may possibly end up letting out the magic smoke.

I didn't vote because the question seems incomplete, no pack voltage stated and lack of servo maker to judge current draw/stall torque etc.