Are 5th Scale Servos Less Likely to Burn out Under Load and Forgiving of High Stress?

[pomplemus]

Hi!

I have pretty unique build in progress making a 6S Kraton into a trail vehicle/rock crawler (I really need to update the build thread) and long story short, I've already burned out several servos.

After killing or 3 spares/cheapos, I decided to throw down and get a ProModeler DS1155 BLHV. Beautiful servos with great performance! But today, after less than an hour of run time, I killed it, letting out the magic smoke. I need to call John at ProModeler and order a repair Job, it will definitely go to use in my basher. Absolutely my fault, the wheels were jammed up between some rocks, and I just kept trying to power through. Where a lesser servo would have stripped, this one kept going , eventually overheating and frying under the constant load.

Anyway, I'm thinking that a standard size servo just isn't going to cut it in a 16+ lb Kraton with 8" wheels, locked diffs, and a driver that really wants a Kraton to go where no Kraton has gone before crawling. Rock crawlers using standard sized servos just aren't normally this big and heavy.

After some staring, I realized if I relocate the ESC and get creative with mounting, I should be able to fit in a low profile or even full sized 5th scale servo.

I have no experience with 5th scale servos myself, so asking the people here with experience, especially in crawlers, are these larger servos that much more durable electrically and likely to hold up under heavy load/jamming wheels between rocks versus standard servos?

Just looking at the specs, they are at least 2-3.5 larger in volume than a standard servo, but draw similar amounts of power to a top tier standard size servo, with specs not too much higher, so I'm hoping that means higher efficiency and less heat due to larger motors, and more area/volume to act as a heat sink and keep things cool?

This build is turning out to be super fun and does surprisingly well as a crawler, its just the servo holding it back, so I really just want to throw down on the best possible servo for the job. I think I've exhausted the peak of standard size servos so perhaps bigger is the answer?

Thanks all!

 

[ColosTommy]

In my 23lbs 6s Outcast based truck, i opted for a full size 1/5 scale servo. I had the space in the chassis and with all the extra weight felt it might be wise.

As i installed it when i built it i can't say whether its any better or worse than a 1/8 scale.

I'm sure someone with more experience with servo's will chime in, but in the mean time i will give your build thread a thorough read, sounds interesting.

 

[pomplemus]

@ColosTommy that sounds awesome, must have been a bear to fit, especially in a shorter outcast. Can you share some pictures of how you mounted it all up and what you have in there?

Thanks, I really need to update that build thread with everything that's been going on the last couple weeks!

EDIT: Just re-found your build thread, definitely an epic one! Looks like a much wider chassis gave you the room you needed in your case.

 

[ColosTommy]

Thanks, I really need to update that build thread with everything that's been going on the last couple weeks!

You sure do!
It's an interesting build, hurry up with the updates and pictures

 

[pomplemus]

Updates to the build thread will be coming later tonight...

I called John at ProModeler a little bit ago, and it looks like at least for ProModeler servos there might not be much benefit in my case going to a larger scale servo. According to John, their servos have so protection/ramp down at all when stalled, they will keep pulling max current right until they burn out. I imagine this is the preferred behavior for a lot of applications, including RC planes, but due to the width and weight of this build, I'm basically guaranteed to jam a wheel between some rocks semi-regularly, and need something that is more forgiving of such abuse by saving itself. He also mentioned the FETs/hot sections of the standard and large scale servos are really similar, so I think if blow FET on a standard ProModeler, the same thing will happen on a large scale.

I know AGF servos have a built in protection that can be programmed to ramp down power when stalled for a time, so that might be preferable. I haven't fried an AGF, but definitely overheated them enough I thing the motor magnets got permanently weakened. Maybe a combination of making the protection more aggressive and loosening the servo saver (super still Treal) a bit would do the trick?

I'd still like to think 5th scale servos are more electrically forgiving of this sort of abuse, anyone with more knowledge that can shed some light? If they really are, I would go for jamming one in, but if not, I might as well just stick with a standard size and try protecting it better.

 

[pomplemus]

I messaged NSDRC with these questions as well. I noticed they claim that direct power servos are more efficient overall, which to me sounds like they may heat up less and be less likely to burn up? Anyone have any experience with this?

 

[Moirae]

I don't know about crawlers but I love my NSDRC servo and it's held up well to my hard bashing in a traxxas xrt.

 

[pomplemus]

Nice, which one specifically do you have in there?

 

[Moirae]

https://nsdrcscaleparts.com/collections/servos-winches/products/rs1-monster-torque-brushless-servo

 

[pomplemus]

Thanks, that's very similar in specs to the NSDRC RS800 V2 I'm considering with the exception of 2s vs 4s lipo power. I would guess a direct power servo is more efficient, will update if I get and answer from NSDRC.

 

[strodedawg]

Anyone need a Spektrum s9110bl servo