What happens if ESC can't supply the amps to a servo?

[chilly]

Just got my first crawler - Capra RTR was on sale cheaper than the kit so I figured I'd start there, knowing I'll upgrade as I go along if I really enjoy it.

Which of course starts with the steering servo! Only the second time out and it twitches a lot but is working generally. I couldn't bring myself to spend 1/3 the price of the whole rig on a new servo quite yet so I just ordered one of the amazon 35kg $30 ones to try.

Question is that I think the servo's peak current is over 3.0A based on some test videos I saw on youtube. The BEC on the RTR's brushed ESC is rated for 3.0A peak at 6.0V. So I'm wondering what will happen if I exceed the draw? Will it just be slightly less powerful at the limit? Or maybe it would jitter or cut out? I know I can add a BEC etc, I'm just curious what would happen if I just toss it in. Which also makes me wonder - could the jittery servo just be a lack of power from the BEC in the first place - and maybe the stock servo is still fine?

Here's a quick youtube video skip to 2:00 you can see how jittery the stock RTR is for me. idk if that's failing or just underpowered?

 

[ferp420]

it will ether just stall or twitch or get hot or burn up all together it could take out the built in bec on the esc aswell but thats kinda extreme
they sell capacitors to help with that they call.them glitch busters if you just need a few extra seconds of steering power
usually you get what we call a brown out were nothing is getting the power you need this causes alkinds of issues cause the reciver is no longer getting a signal cause well not enuff power 98% of the time everything is fine but every once and a while something burns up
for most the bigest issue is pausing to let the bec catch up lol
nothing worse than being in the midle of a hard glimb and having to stop and let the power ramp back up

 

[chilly]

they sell capacitors to help with that they call.them glitch busters if you just need a few extra seconds of steering power

Oh that explains the capacitor! The rtr does have one with a sticker on it saying "do not remove" lol. It's inline with the dig servo, but I guess the power supplied on the 6V BEC is all one circuit so it would affect all servos (I think?).

 

[ferp420]

direct power servos solve alot of problems atleast for steering
ive seen them as low as $35 but usually around $45 for a cheap jx 37kg vertion
a shift/dig servo as long as there adjusted right dont have any load on them so they dont draw much power

 

[cartronicshn]

Also an external bec will do the job, and you can use that further down the line if you stick around and get one of the better servos.

 

[King Dork]

If you get an external bec make sure to also get a bypass adapter and research how to wire it up. Will save a lot of disappointment.

 

[mikemcE]

If you get an external bec make sure to also get a bypass adapter and research how to wire it up. Will save a lot of disappointment.

Critical!! Brown out from servo draw can do funny things that you don’t need, loss of steering when wedged in combination with no throttle because it reset. Big servos need bigger power, 5amps works, Ten is better


Hang up and Drive

 

[Voodoobrew]

The bec in a hobbywing 1080 esc has alwayse been enough for me. Something to think about if stock esc is brushed. It's only a $40 esc compared to a $20 bec.

And you only hit 3a if your servo is bound up

Use a shorter servo horn and bump up the endpoints if you can. It's like gearing down a servo.

Also make sure the servo stops before it locks up on the endstops. Forcing the servo against the endstops will kill them fast.


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[chilly]

So many options! Ok I bit the bullet and ordered a BEC and a bypass. I'm hesitant to buy a 1080 ESC since the RTR one (Dynamite AE5L) seems to work fine otherwise (it always turns the wheels?), and you can always use a good BEC down the road if things change anyway. And this way I can burn through cheap servos and keep using the BEC as I learn my lessons (assuming IT doesn't burn out). The Castle BEC seems to have a big cap on it too so hopefully this will all stop the twitching servo one way or another.

 

[bgredjeep]

In the case of my esc70 and a servo that can pull close to 5amps. When I jammed the steering up pretty good the esc triggered a safety (beeped at me a couple times) and basically turned off until I freed it up.

I guess that's better than roasting itself, but I would rather the steering just work so I ordered a bec. Next time I buy a servo it'll be direct power to just bypass those issues all together.

 

[Gula]

Brownout.

 

[chilly]

So after all that hand wringing and not being able to make rhyme or reason about why my servo is twitching when it is (not even at high load... and with a big cap).... it turns out it's my friggin' radio.

I got one of those flysky g7p radios which has great functionality for the price. But I was playing with a carpet buggy yesterday and IT was twitching like crazy too. So I finally figured it out - you can see the channel levels on the display just jumping around. Less than 90 days old and luckily amzn will give a refund. But now I'm all in with 5 receivers, so I have to stick with that one for now and get another. Hope for the best I guess.

 

[ferp420]

did you calibrate the radio ? its vary posable the deadband on the radio isent playing nice with the dead band of the servo
i just had to recalibrate my flysky to fix a throtle walking issue its fine now but after years of use i found 1 esc it dident like and recalibration it fix it

it still sounds like its the endpoints though

 

[chilly]

So I got the replacement radio today and that fixed it. Oh well I'm going to wire the BEC anyway for a bigger servo. And hope this radio doesn't have a problem. At least they let me export and reimport my models - although have to rebind each.

 

[this1dude]

In the case of my esc70 and a servo that can pull close to 5amps. When I jammed the steering up pretty good the esc triggered a safety (beeped at me a couple times) and basically turned off until I freed it up.



I guess that's better than roasting itself, but I would rather the steering just work so I ordered a bec. Next time I buy a servo it'll be direct power to just bypass those issues all together.

What servo were you using? Cant seem to find any servos that list the amps theyll draw

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[SleptOver]

What servo were you using? Cant seem to find any servos that list the amps theyll draw

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I bet he measured or calculated it based on wattage divided by voltage.