Castle MMX 8S BEC powerful enough for all 1/5 scale servos?

[NorwegianBasher]

Hi

According to Castle the Mamba Monster X 8S BEC specs are: "Powerful Integrated 8A Peak Adjustable BEC (5.25V-8.0V)"

However, a powerful 1/5 scale servo will require more than 8A peak under heavy/peak load. For example, the servo I am considering to combine with the MM8S is the PowerHD WH65. It`s rated at 10A stall current at 6v and a whooping [email protected]. I want to run the servo at 8v driving non-stop on bumpy grass with a strong servo saver spring.
I did see this exact combination in a youtube video in a K8S. No issues in the first 15min test drive on grass, but I suspect I will be pushing the servo/BEC a bit harder.

On a side note, the AGF A280BHMW is rated at 11-13A(depending on the spec sheet) @8,4V. In general it seems the powerful 1/5 scale servos can peak far beyond the rated 8A of the MMX 8S.

Just wanted to check with you guys if anyone have experienced issues. I don't want to try the combo and risk any issues with the ESC or not getting good power out of the servo. Currently running Hobbywing Max ESC, but I would like some of the Castle features. Would be nice to avoid the heavier and more expensive XLX2 with 20A peak BEC if not needed. Not interested in running an external BEC and quite certain I am happy with the power of the MMX 8S.

 

[Diem Turner]

I think you kind of already answered your own question. If the servo can pull 15A, then 8A isn't going to be enough. You're either going to need the XLX2 or a separate BEC and battery.

 

[Moirae]

You really should have got the xlx2. =P

 

[Cereal_killer]

Either get a bec from castle. Or as other say xlx2. Should use a xlx2 for a 5th scale... Mmx8s would probably be too weak anyways

 

[dure16]

Which vehicle and tires do you have? Are you set on that servo?

 

[DLK83]

You can also run a splitter harness and a separate, small, 2s battery to directly power the servo, that's what I do with the Promodeler servo in my Xmaxx

 

[Moirae]

You can also run a splitter harness and a separate, small, 2s battery to directly power the servo, that's what I do with the Promodeler servo in my Xmaxx

This is a great idea tbh.

 

[DLK83]

This is a great idea tbh.

Yeah, Promodeler heavily urges the people who buys his servos to run that setup, and after NOT taking his advice, I got to experience a "brownout" first hand.. i tried running his DS950 servo thru the receiver like normal,, and I would get all kinds of weird/delayed throttle response after the batteries were about 1/2 done, I thought it was the esc at first, but it was the servo maxing out the bec in the esc.. ordered his little kit with the splitter harness and small 2s LiIon battery, and problem solved
And yes, I know a stand alone bec will do the same thing, but it's still pulling from your main battery/batteries, which equals less runtime, and more power going to the servo instead of my itchy trigger finger... and the cost of the harness and battery is less than a bec, only downside is 1 more battery to mount somewhere and charge

 

[NorwegianBasher]

This is for an X-maxx with stock tires. Upgraded servo saver spring with additional spacer for even more stiffness. I do not want the car to become heavy. Currently using a Max 5. Considering to swap it for a Max 6 I have because I don't like the size, placement and weight of the Max5. I think its excessive and that the Max 6 is enough for stock motor size. I want to keep the stock motor size/weight. So not interested in an XLX2.
There is a nice deal on a MMX8S locally, so I started to play with the idea of buying it for my X-maxx instead of using my Max 6. I could borrow a MMX8S from one of my 6s KEXBs and try it in the X-maxx, but by the time I have made a conclusion I assume the deal is gone. Hence asking for advice about the ESC in this thread.

The chassis have been modified for the 1/5 scale WH65 servo. With an extra-extra stiff servo saver I feel more comfortable with the much beefier 1/5 servo gears. Much lower cost too compared to a high end regular size servo.
I have looked at solutions with various BECs or a servo battery. I consider those spare options, but would prefer to run the servo of the ESC if possible. Less weight, less hassle with battery charging and monitoring, less stuff to go wrong ,less stuff to be in the way when working on the car, less cost and possibly a more constant voltage from start to finish of the run (compared to a tiny battery).

If I were to do it again I probably would have used a regular sized 4S AGF servo, ran it directly from one of the batteries. Then made my 6 fan motor setup suitable to run directly from the other battery and used my Radiolink RC6GS voltage telemetry (with alarm) hooked up to the battery with the lowest voltage.
Or just ran a good 2s (8A peak) servo from the MMX8S.

Despite what the paper specs on the MMX8S say and various 1/5 scale servos demand. In real life there seems to be multiple people running it fine with a 1/5 scale servo. On youtube, Innovation RC, Earl Moorhead and Jason Perrin have been running it in a K8S. Not seen anyone reporting any issues, but I don't follow those guys either so not sure what the long term results are. The MMX8s also have a built in "BEC over temperature warning". So still wondering if the ESC can handle it, or at least not be damaged.

 

[DLK83]

That's my setup.. battery comes out in seconds if I need to work up front, weighs pretty much nothing in comparison to the overall weight of the truck, and only needs to be charged every other/every third set of batteries and charges in 15 minutes

Just finished the fan setup, just have to figure out where I'm putting the battery.. ran a test last night, those are 40x28 server fans, ran them for about 35 minutes, checked the battery, all 3 cells at 3.95... I could probably run 2 sets of batteries thru the truck before having to charge either one of the small batteries, and no chance of a brownout and I'm getting the most I can out of my main batteries

 

[NorwegianBasher]

The servo setup is nice. I highly considered it/making it myself when I was running the stock Traxxas radio and esc.

Personally I prefer a low amount of batteries/running everything from the main batteries. Better optimization with less hassle IMO.
I've had zero issues with the Max5 and PowerHD WH65 wired through the Radiolink receiver. Max 5/Max 6 have the same BEC specs, 6A cont/25A Peak according to Hobbywing. If I did experience any issues, or used a lower voltage receiver I would just solder a custom "power bypass" wire from the receiver to the servo.

Anyway, out of curiosity for a more official answer to my question. I have asked Castle about the MMX 8S ESC in combination with 1/5 scale servos. Will update with their answer.

 

[NorwegianBasher]

Jason Miller - Product Specialist @ Castle answered:

The internal BEC should be fine for that application as long as you set your endpoints correctly so it doesn't stall.

So basically it should work.

I put the ESC in my X-maxx for a short test run on bumpy terrain with grass (increased workload compared to most terrain). PowerHD WH-65 with extra long servo horn (trading a bit kg for more speed) which in general gives it increased workload. Upgraded servo saver spring (increased workload). Shimmed servo saver for even less "servo saver understeer" (increased workload). Stock X-maxx 8S motor fans (2x40mm or 35mm?) + an additional 4 30mm low current fans on the sides of the motor (increased workload compared to stock). Stock fan on the ESC connected to the ESC. Noticed zero issues with all that stuff. If there are any, I will report back.

(The whole 6 fan motor fan solution draw a maximum of 1,2A@8v, so not that much, but its fairly quiet for the cooling effect it provides. I prefer not to have my cars sound like an airplane ready for take-off.)

I also asked Jason about the stock fan power output on the MMX8S and he told this was only good for about 0,5a. So for anyone wanting to upgrade to a powerful fan above that. Connect it to the receiver.

I paired the ESC with the stock X-maxx motor (non-censored) for this testing and was very surprised on how smooth it was at low speed/startup compared to the Hobbywing Max 5/6. I knew these ESCs were smooth with a sensor. But why have no one told me how smooth they were even without a sensor? Very impressed!
Ill have an additional MMX8S in the mail next week since one of my Kratons are missing one and most likely wont get it back. ;p