Lifespan of a cheap servo?

[El Gecko]

Talking about those MG996 that you can get in bulk, and in this particular case it's sealed in a plastic bag for waterproofing.

The question is, why do I keep burning them out on long trail walks (2 miles/1hr)?

When I crack open the servo case to see what's wrong, there's a really intense "burning electronics" smell, and the servomotors still run if I hook them up to a battery, but the controller IC inside the servo seems to have melted.

Can it be that I've just overused them to the point of failure? (the exact failure being a burned out circuit board)

These are not particularly tough trails (it's a 2WD monster truck with open diff, after all) so I would assume that a servo could last longer than an hour of continuous usage but maybe not??

Am I suffering effects of water damage? The cases are still dry inside when I open them up, and the bags that I use for waterproofing are always dry inside after even the messiest drives, so maybe it's a water vapor thing?

I'm not too concerned/upset because they were cheap to begin with, but I was hoping to hold off a bit longer before I drop the coin on a better servo (maybe waterproof this time!)

However, losing two servos practically back to back has prompted a rethink. Am I expecting too much from these cheap servos?

[Juggular]

Have you tried a different ESC? Perhaps using a separate power source through BEC might work better? 

Most ESCs would bring the voltage down to 5-6v for receivers & servos (Hobbywing 1060 gives you 5v but higher 2A, Tamiya ESCs give you 6v but lower 1.5 amp).  But if the step-down-regulator is defective on the ESC, it might give your receiver full voltage of the battery. 

Most receivers are fine up to 8.4v, so receivers are not the first thing to burn out. But most servos are designed for 4.8 - 6v (unless you get a "high voltage servo.")  So, if the ESC gives you a higher voltage, servos tend to get fried before receivers do. Even a $100 servo can burn out at 9v (when the LiPo battery is fully charged).  

Your option might be; 1) try a different ESC to see if the power output to the receiver is nice 5 or 6v.  (If servos burn out at 5-6v, then they are the defective ones.) 

2) or try external BEC.  These things can take up to 26v (7S) and bring it down to 5 or 6v (less than than 2S) for the servo.  More importantly, they can supply more amp.  Below is a Turnigy one. 

https://hobbyking.com/en_us/turnigy-5a-8-26v-sbec-for-lipo.html?wrh_pdp=2&utm_source=google&utm_medium=cpc&utm_campaign=google_us_shopping&countrycode=US&gclid=EAIaIQobChMI0c74pZGj9gIVwZ-zCh0tugQ-EAYYASABEgJde_D_BwE&gclid=EAIaIQobChMI0c74pZGj9gIVwZ-zCh0tugQ-EAYYASABEgJde_D_BwE

 

[alvinlwh]

What ESC are you using and what V it is (supposed to be) putting out? As suggested, if too high, use a UBEC. 

[MadInventor]

If you're sealing it in a plastic bag then water can't get in, but heat will find it harder to get out. (You've wrapped it in an insulator). Perhaps trying running it without the bag. Also if it's being used in a monster truck then perhaps it's struggling just turning the wheels when it's stationary. 

Also have you checked that the steering isn't hitting bump stops and loading the servo (Does it buzz slightly at full lock when the front wheels are off the ground) ?

But it does sound like it might be the rx supplying too much voltage as the others have mentioned.

[Jonathon Gillham]

I've had a similar experience with the MG995 which are also cheap and sold in lots of 4. The 2 which I used as steering servos in cars failed quickly, probably 5 - 10 runs which were pretty gentle. One took the ESC with it, the other didn't but it made it appear that it was another issue but the car is running fine now with the same rx and esc but new servo.

I have since tried other servos like SPT and JX and never had an issue, despite them being cheapish for decent specs. Admittedly, one of these cost the same as 4 of the MG995.

[WillyChang]

Check your EPA endpoints settings. 
 

When your EPAs are making servo try to travel further than linkage/steering has available, jammed servo will overheat and cook itself. Higher torque servos burn up even faster when jammed as they are able to pass higher current. 
 

Set EPAs so that servo just reaches full lock. Servo should be silent at both ends; it should never be heard clicking or straining.  

[WillyChang]

that said...

MG996 was great value 20odd yrs ago when they appeared on the market alongside other newcomer budget brands like Bluebird etc, predating emergence of the Hobbyking empire. Proper original MG996 weren't dirt cheap, think they were like 1/4-1/3rd price of similar spec Hitec etc. Coincided around the time of HPI Savage's heyday.

But then MG996 got copied and cloned repeatedly... not even sure who the original maker was anymore (had a purple sticker from vague memory).

Prices dived as clones undercut each other dog-eat-dog, dropped to like 1/5th what they were asking earlier on... you need only imagine what that cost-cutting does for quality/reliability.

 

[El Gecko]

Thanks, I think I may just be overworking these cheapo servos--after a bit of googling around, it seems to be a common issue.

The ESC is a Traxxas XL-5 which puts out 6V to the Rx (Flysky 2.4Ghz), and all is perfectly fine when I swap in a new servo. Both times it happened on the second battery pack in a row (5000mAh NiMH), and it always has plenty of power to turn the wheels (except in certain extreme situations).

I do think the waterproofing plastic bag traps more heat than usual, and it's tucked away inside the chassis pretty well, so I'm guessing the electronics are just overheating.

On closer inspection, there are little bubbles on the transistor on the circuit board inside the burned out servo which appears to confirm this.

The steering is non-bellcranked, direct tie rods from the servo saver to the knuckles, so it could be torquing on the servo over bumps (the suspension is really soft, so there's a lot of movement).

And now that I'm realizing it, there was definitely a lot of back-and-forth on the steering both times it happened, since I had to countersteer a lot on the slick snow. There's no EPA on my Tx, so that could have an effect too.

Overall a lot of contributing factors, but mostly I think the conditions were just too extreme for the servo to handle. I did have one of these fail in a Grasshopper already too, so a 2.5kg monster truck might just be a bit too much for it. Or I need to finally pony up for a Tx with EPA

[Willy iine]

@El Gecko As for life span of my cheapo violet colored Amazon 20kg servos I run in most of my M38's and a few GF01's, all of them have been working perfectly and absolutely no issue.  I was quite skeptical as I usually run Futaba, Savox, or at minimum Spektrum (all digital servos) but these cheapo digital servo's have been great so became my go to servos for short wheelbase cars.

My ESC is mostly old TBLE02S (the ones that were good) and 1060.   I do set up the EPA as the torque is so high it can damage the car and/or servo mounts.

This is the servo on my 58044 Pajero.

 

[El Gecko]

Thanks @Willy iine I will have to check those out once I upgrade my radio.

Meantime I think these were great to get a bunch of my cars on the road, but now they will gradually get replaced with better quality stuff (which was always part of the plan anyway, I just didn't expect it to happen this soon).

According to this review even a Futaba S3004 should last longer than these

http://www.rcmodelreviews.com/mg995review.shtml

Does anyone have experience with JX servos? I found one that's 120 degrees like the Futaba, so maybe I can run it with my non-EPA Tx for now. The biggest issue with the Amazon 20kg/25kg/30kg/etc cheapos is that they all have much larger control angles, requiring the use of EPA. The most common are 180, 270, 360, and even continuous rotation, so finding (good, cheap) 120 degree servos has been a bit of a challenge. I don't remember what the MG996 I got were advertised as, but I think I took a chance and they turned out to be 120 after all (confirmed by looking at the stop points inside the casing).

[alvinlwh]

5 hours ago, Willy iine said:

@El Gecko As for life span of my cheapo violet colored Amazon 20kg servos I run in most of my M38's and a few GF01's, all of them have been working perfectly and absolutely no issue.  I was quite skeptical as I usually run Futaba, Savox, or at minimum Spektrum (all digital servos) but these cheapo digital servo's have been great so became my go to servos for short wheelbase cars.

My ESC is mostly old TBLE02S (the ones that were good) and 1060.   I do set up the EPA as the torque is so high it can damage the car and/or servo mounts.

This is the servo on my 58044 Pajero.

 

How did you get a 02 (or even a 1060 with 3A) to power a 20kg servo??? I don't see a UBEC in your set up. I cannot even get my 04 to work properly with a 9kg JX one! 

[alvinlwh]

27 minutes ago, El Gecko said:

Does anyone have experience with JX servos?

I have JX 9kg low profile ones. They causes no end of problems with my Tamiya TBLE-04S due to low BEC current. I am awaiting delivery of some better ESCs to use with them. I tested them to draw 3.2A off car, so could be higher when installed. 

[El Gecko]

5 minutes ago, alvinlwh said:

I have JX 9kg low profile ones. They causes no end of problems with my Tamiya TBLE-04S due to low BEC current. I am awaiting delivery of some better ESCs to use with them. I tested them to draw 3.2A off car, so could be higher when installed. 

3.2A on the bench maybe the JX is a bad idea then!

Does anyone know what kind of servo the cheapo RTR crawlers come with? I don't see a lot of servo failures in the reviews, so they've gotta be using something halfway decent at least. Then again, maybe the included Tx has EPA on it, which puts me right back down the "new radio" path.

[Willy iine]

22 minutes ago, alvinlwh said:

How did you get a 02 (or even a 1060 with 3A) to power a 20kg servo??? I don't see a UBEC in your set up. I cannot even get my 04 to work properly with a 9kg JX one! 

I don’t use capacitors.  Works fine!    

[alvinlwh]

33 minutes ago, El Gecko said:

Does anyone know what kind of servo the cheapo RTR crawlers come with?

I believe your main objective is waterproofing? I use an Etronix ES060 6.0KG for my waterproof car. 

[alvinlwh]

29 minutes ago, Willy iine said:

I don’t use capacitors.  Works fine!    

The 02 and 1060 BECs must be far more capable than their numbers suggest. 

[Willy iine]

7 minutes ago, alvinlwh said:

The 02 and 1060 BECs must be far more capable than their numbers suggest. 

I guess so.  I have no clue, never really cared to check the numbers to tell you the truth!

[Jonathon Gillham]

9 hours ago, El Gecko said:

Thanks @Willy iine I will have to check those 

Does anyone have experience with JX servos? I found one that's 120 degrees like the Futaba, so maybe I can run it with my non-EPA Tx for now. The biggest issue with the Amazon 20kg/25kg/30kg/etc cheapos is that they all have much larger control angles, requiring the use of EPA. The most common are 180, 270, 360, and even continuous rotation, so finding (good, cheap) 120 degree servos has been a bit of a challenge. I don't remember what the MG996 I got were advertised as, but I think I took a chance and they turned out to be 120 after all (confirmed by looking at the stop points inside the casing).

Yep, I have the JX 4409MG and no issues at all. They perform well. I'm not sure if their claimed specs are real, but they are far better than I need in my basher cars anyway. No issues with brownouts or anything either, and thats on TBLE-02S, HW 1060 and Surpass 60a brushed ESC