Trampa - E-Toxx EMTB with 12S Roxxy ESC, Beltdrive SK3-149kv


In fact that there is a big need for good 12S Esc´s for use in MTB i started to test some new one.

The ESC´s are from Robbe and called 9120-12S OPTO

The footprint is similar to the MAX6 only 3mm longer and lower in hight.

This ESC is longer then 5 years on market and is marked as a universal ESC for Car, Boat, Plane and Helicopters.

I bought the optional Programmbox wich is very nice helpfull tool

You can set all needet parameters easily with the programmbox!

Most parameters can be changed like aceleration, timing, reverse, pol numbers etc…

But the brake strenght cant be changed! The amount of brakepower is good IMO so its no big downside for me. Also you have to get on with the trigger way for braking : The board starts to brake on maybe 80% of the trigger brakeway ! So you have only 20% of the normal trigger way. Anyway the brake is proportional and QUITE and good. I get really fast on with it. Maybe if you use better RC-type controllers you can play with settings linke EXPO to get more triggerway.

I rebuild my Beltdrive Trampa with these Roxxy´s

Its a HTD 5 drivegears 25mm width, reduction of 1:6 with a roller and support bearing holder

I use my Hobbywing MAX6 Carbonfibre plate for the Roxxy´s. They comes without mountingholes so i use double sided 3M to mount on plate.

The Roxxys are OPTO Esc´s that means the have no build in BEC. I use an MTEC Keto HV BEC V2, it delievers up to 10A continuous current (-; absolutely overkill but its quality stuff and maybe anyday i can use it for supply anything :innocent:

Batteries are Hobbyking stuff : 6S 5000mAh 60C Zippy Compact, wired in series for 12S !

Motors are actually the SK3-6374-149KV

First 2 testruns are really impressive. The startup is very good, the acceleration is brutal (-; The thing is a beast, it has such a nice feeling on trigger! It has an absolutely direct feeling, even on low rpm´s …

Will do some video footage on next run if it will stop to rain today (-;

Hang Loose Jenso


So as i promised some video stuff from the afternoon:


Congrats on finding this exact esc, seems to work quite ok for the needed application… :slight_smile:

Although - I had a mechanical question - How much of the motor pulley is sitting on the motor axle?

I’m wondering because my sk3 motor is still on its way and axle lenght for sk3 6374 I believe is 27mm… (from what I could figure from the shematic shown on

So I cannot get my head around how did you manage to fit 25mm belts, if the pulley is probably 27mm… + motor mount which seems also almost 6mm if not 8mm in thickness + a little bit of spacing between motor mount.

During the rain i changed the Aluminium Braces to Carbonfibre ones. They are also 8mm thick but in total wheight drops about 110gramms.

It still rains so i milled some slots in the spacers with a roundhead miller, saves 1gramm per piece LOL just kidding its more for the look :joy:

After good performance tests with the Roxxys yesterday i decidet to test if even more Power is possible :smiling_imp:

I prepered some 192KV Turnigy´s with the 12tooth pulleys :

@Okami : As you can see here i “extend” the Motorshaft with some “silversteel” round material. About the half of Motorpulley sits on motorshaft, the rest is supported … Motormounts are 10mm thick btw.

192kv Turnigys mounted on Rig :

Have done 3 runs with the new motors today, its hard to describe in words man :scream: You dont even feel an drop in acceleration, it just going straight forward with a speed that is awesome! Topspeed is calculated with 54kmh equal to nearly 34mph. The tires are looking for grip but they had a hard time :sunglasses:

I will try soon to get this performance on video, not sure whats best for demonstrating… keep you updated

Hang Loose


Hi Jens, another awesome build!

Do you think it’s possible to make the ESCs and BEC as tidy as in your Hobbywing Max 6 build?


Hey. Thank you David.

Its hard to get the UBEC and RC in the Traxxas Box. I´m looking for a clean solution.


That’s clever… I always wondered doesn’'t the ‘‘one sided’’ belt load makes the motor suffer… I suppose you really have an engineer’s mind to come up with this solution… thought why you have that weird extra dot in the mount, now I know why :slight_smile: - the shaft extender

About the tires - have you found ones that last more than just a couple of rides? :smiley: I hope I’m not joking but I think you said once that your burned through some tires in only 1 or 2 rides… crazy… almost like drift rider, who needs a couple of extra set of tires after each drag race…

I hope someone comes up with a ‘‘mechanical how to’’ for tackling all the little things involved in making a motor mount etc… have not found a comprehensive how to guide so far :slight_smile:

Another awesome build man !!

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I have an Etrampa with similar wheels and I’ve put over 100 miles so far without much wear on tires. A lot of those miles were off road but I don’t think the asphalt does a whole lot of of wear

Not sure how much ply / layers has these… but I do remember someone posting that after a while their tires where in quite bad shape… this thing kind of set me back a little bit when I was only starting to collect info about building a mountainboard…

Oh yea they’ll wear out faster than thane but not two rides that’d be nuts. These tires aren’t cheap haha

It depends on driving style and type of tires of course. Burnouts on split are not the tires best friend. IMO the Alphas wear out more then the other tires, but you dont have to forget that this is the lightest tire, all other have about 100gramms more per wheel. My favorites are Trampa Mudplugger, but not for concrete use. Very good in the woods or on hard dusty dirttracks.

I mount them on the driven truck in wrong direction, better traction IMO. Thanks to “BruceLee” …

On the front they mounted correctly.

Have had some more runs on the 192kv :smiling_imp: Hot in Germany about 30degrees. Motors get real hot after heavy abuse, about max temp of 80degree inside on the coils. Batteries gets 40degrees ESC about 37degrees (-;

I need about 800mAh for 1km, by agressive riding …

Have an look, got some video footage from yesterday.

Hang Looose Jenso


@Nowind Can you name a few reasons why exactly you chose 25mm belt? Have you had problems using 15mm or 25mm is just more durable / more power?

As for the tires… I think I recall that skike wheels/tires were quite bad in terms of durability although I should check whenever this was true… :slight_smile:

so yeah, it looks like mountainboard tires are sturdy enough and wouldnt become naked just after a few rides

Hey. A friend of mine got tested the 15mm Belt with highpower 12S Setup and have had lots of problems. Thats why i direct took the 25mm belt.

Greetz Jenso

I see. Thanks for answer… :slight_smile:

Touring Setup with 12S 12400mAh :

Race/Freestyle Setup with half the batterie:

Greetz Jenso


Check this Video :imp:


:open_mouth: dude… holy shit!

Good thing you weren’t wearing pants.

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wow dude, I guess Roxxy are no go for you now? Did you work out what the cause was? overheat? short circuit? evil bastard poured petrol all over your esc?

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