Build Thread Exige's Mugen MBX8Te truggy - the used parts special

[81exige]

So as some of you already know, recently I acquired a low-mileage Mugen MBX8T Eco roller as the former owner needed the fund for a new nitro buggy. https://www.rctalk.com/forum/threads/surely-this-isnt-that-bad-of-a-deal.148444/

At that time I thought it was very good of a deal, and since it flew under everyone's radar (the big boys here always target 1/8th scale buggies), plus I needed something solid to re-enter the hobby. I decided to check it out. This is my first race-level vehicle, and being a Mugen Seiki, parts support is fairly good (in Vietnam, HongNor is usually the primary choice when moving to higher-level vehicles, then Mugen, then probably a tie between Associated and XRay).

Pics from the previous owner:

According to the guy, he bought the vehicle already with some mileage on it, and on the surface it appeared fine, except for a faulty front diff pinion gear that caused severe cogging in the front. He swapped it out and refreshed all 3 diffs but left the shocks untouched as he didn't think they need any servicing. He then proceeded to not put an extra mile on it, until I came along and bought it from him.

It has so little drivetrain wear you can basically sell it as new and no one would probably notice...as long as you don't look at the front tower which had a minor ding.

My goal would be to eventually turn this thing into an on-road basher with acceptable handling characteristics like how everyone here drives their buggies - nitro or electric, because, as odd as it may sound, there's more paved surface to drive around here than there are unpaved ones. It won't have all the bling as this fine gentleman's buggy right here since I'd like to see what sort of vehicle I can get on a budget (but no, that won't mean I will cheap out on everything). https://www.rctalk.com/forum/threads/surely-this-isnt-that-bad-of-a-deal.148444/

I will update this thread as I progress further with the build, whenever I have the free time (so very slowly).

Oh and lastly I'd like to blame @Warby and @Littlemotor for their delicious, gorgeous, finger lickin builds tempted me into securing this thing.

 

[RustyUs]

Awesome! Crack that thing open and get to it.
I look forward to your progress. Enjoy

 

[Littlemotor]

Congrats sir. Looking forward to the progress.

 

[Warby]

 

[TeknoJ]

Score, that trugg looks very nice

 

[Warby]

Oh and lastly I'd like to blame @Warby and @Littlemotor for their delicious, gorgeous, finger lickin builds tempted me into securing this thing.

 

[81exige]

Small update: got a motor and ESC. Nothing fancy, but it works. Hobbywing EZrun Max 8 ESC + 2200kv motor (sensorless, used). I do see what looks like surface rust just surrounding the screws holding the motor cap in place though.

Next step is to mount it to the car. As it turns out the ESC mounting plate isn't big enough to also mount the power switch. At the moment I have 2 ideas of how to mount the switch. The first is to stick it right inside the battery tray and cut a foam block to separate it from a battery that will eventually go in there. I sacrifice a bit of space for bigger batteries this way but I can probably get around this with taller packs.

The other way is to stick it to the side of the ESC.

Any ideas?

If you're wondering about the gear mesh, I'll get to that later—it's apparently easy enough to get right (the good ol "stick a piece of paper into it") that I won't do it right now.

Also, this will eventually see a lot more time on tarmac and concrete rather than on the dirt. My objective is to make it *not* pop a wheelie every time I hit the gas so I went for a 19t pinion gear instead of the kit recommended 15t. Spur gear is stock, as are the ring and pinion gears for the diffs. Tires are P-L Hole Shots measuring 135mm in diameter. Car will be run primarily on 4s. Would this be too tall a gearing? Let me know.

 

[Littlemotor]

Small update: got a motor and ESC. Nothing fancy, but it works. Hobbywing EZrun Max 8 ESC + 2200kv motor (sensorless, used). I do see what looks like surface rust just surrounding the screws holding the motor cap in place though.View attachment 265266
Next step is to mount it to the car. As it turns out the ESC mounting plate isn't big enough to also mount the power switch. At the moment I have 2 ideas of how to mount the switch. The first is to stick it right inside the battery tray and cut a foam block to separate it from a battery that will eventually go in there. I sacrifice a bit of space for bigger batteries this way but I can probably get around this with taller packs.View attachment 265267
The other way is to stick it to the side of the ESC.View attachment 265268
Any ideas?

If you're wondering about the gear mesh, I'll get to that later—it's apparently easy enough to get right (the good ol "stick a piece of paper into it") that I won't do it right now.

Also, this will eventually see a lot more time on tarmac and concrete rather than on the dirt. My objective is to make it *not* pop a wheelie every time I hit the gas so I went for a 19t pinion gear instead of the kit recommended 15t. Spur gear is stock, as are the ring and pinion gears for the diffs. Tires are P-L Hole Shots measuring 135mm in diameter. Car will be run primarily on 4s. Would this be too tall a gearing? Let me know.

Personally, I like to keep footprints as tight as humanly possible-but also the shortest cable run’s I can manage as well. I’d likely coil the cable down a driver to tidy that up, and then use servo tape to secure it on the outboard side of the ESC on the stone/mud guard.

This would also keep the battery tray space available to run the longest pack possible in order to keep CG low.

I haven’t run a Mugen trugg in many years-so I cannot comment on the gearing without knowing the actual rollout math.

As for wheelie control-I’d prefer to combat it with center diff tuning, over extra load on my electronics. You will have enough of that due to running on asphalt/tarmac.. I’d say try the 19T, and if it gets your electronics hotter than is acceptable-then run a 40mm fan on your motor, and retest. If this were my Tekno, I doubt I’d wanna go much higher than a 17T with a 2200kV. This is also dependent on tire circumference, obviously.

Last thing I’d recommend would be a steel spur, since you’re not on dirt, and will be ridiculously hooked up.

 

[81exige]

Appreciate your support good sir.

Personally, I like to keep footprints as tight as humanly possible-but also the shortest cable run’s I can manage as well. I’d likely coil the cable down a driver to tidy that up, and then use servo tape to secure it on the outboard side of the ESC on the stone/mud guard.

so, coil the wires for the power switch, then use servo tape to mount it to the ESC's side?

I haven’t run a Mugen trugg in many years-so I cannot comment on the gearing without knowing the actual rollout math.

As for wheelie control-I’d prefer to combat it with center diff tuning, over extra load on my electronics. You will have enough of that due to running on asphalt/tarmac.. I’d say try the 19T, and if it gets your electronics hotter than is acceptable-then run a 40mm fan on your motor, and retest. If this were my Tekno, I doubt I’d wanna go much higher than a 17T with a 2200kV. This is also dependent on tire circumference, obviously.

from the parts list of the stock car: 47T center spur, then 46T for the diff ring gear and 10T for the bevel/pinion gear. No idea about tire ballooning radius for Hole Shots since those are made for track instead of high speed use, but assuming something like 145mm, I punched those into the RCT rollout calculator and got a rollout of 2.23:1. I will eventually go with some smaller (about 105mm dia. or smaller) GT tires to justify running that 19T motor pinion.

I'll think about the steel spur. I saw a steel OEM replacement for the stock one but the price means I have to hold back a lil bit lol.

 

[Littlemotor]

Appreciate your support good sir.

so, coil the wires for the power switch, then use servo tape to mount it to the ESC's side?


from the parts list of the stock car: 47T center spur, then 46T for the diff ring gear and 10T for the bevel/pinion gear. No idea about tire ballooning radius for Hole Shots since those are made for track instead of high speed use, but assuming something like 145mm, I punched those into the RCT rollout calculator and got a rollout of 2.23:1. I do tend to eventually go with some smaller (about 105mm dia. or smaller) GT tires to justify running that 19T motor pinion.

I'll think about the steel spur. I saw a steel OEM replacement for the stock one but the price means I have to hold back a lil bit lol.

Mount it to the plastic stone guard/mud guard, PARALLEL to the ESC, but not attached TO the ESC..

Massive difference in the tire heights (more accurately; the circumference) you listed… Try the 19T, and verify your temps don’t exceed 180F. If they do, drop a tooth on the pinion, and retest. If it’s still high, run a 40mm fan.

That plastic spur will not last long in the street. If you do not do it now, you will have to when it fails.

 

[RustyUs]

Small update: got a motor and ESC. Nothing fancy, but it works. Hobbywing EZrun Max 8 ESC + 2200kv motor (sensorless, used). I do see what looks like surface rust just surrounding the screws holding the motor cap in place though.View attachment 265266
Next step is to mount it to the car. As it turns out the ESC mounting plate isn't big enough to also mount the power switch. At the moment I have 2 ideas of how to mount the switch. The first is to stick it right inside the battery tray and cut a foam block to separate it from a battery that will eventually go in there. I sacrifice a bit of space for bigger batteries this way but I can probably get around this with taller packs.View attachment 265267
The other way is to stick it to the side of the ESC.View attachment 265268
Any ideas?

If you're wondering about the gear mesh, I'll get to that later—it's apparently easy enough to get right (the good ol "stick a piece of paper into it") that I won't do it right now.

Also, this will eventually see a lot more time on tarmac and concrete rather than on the dirt. My objective is to make it *not* pop a wheelie every time I hit the gas so I went for a 19t pinion gear instead of the kit recommended 15t. Spur gear is stock, as are the ring and pinion gears for the diffs. Tires are P-L Hole Shots measuring 135mm in diameter. Car will be run primarily on 4s. Would this be too tall a gearing? Let me know.

At least you got a lot of real estate to work with. I wouldn't mount the switch directly to the ESC unless you absolutely had to. Mount the switch beside or behind the ESC. For off-road situations that may involve debris, I'd probably opt for securing the switch on the chassis, behind the ESC, in order to have better escape path along the side guard.

 

[81exige]

Steering servo should arrive in about a day or two, in the meantime I decided to tape the ESC + switch like this. Are the motor wires being twisted like that of any concern? And with the ESC wires being perilously close to the spur gear, what would be the best way to run the wiring here?

more of a side question, but how come the part number for the rear tower is E2563 per the manual, but per the parts list and every website it's E2568? printing error maybe?

 

[81exige]

I noticed that the mounting screws for the front shock tower will not budge. The lock nuts can come off; it's the mounting screws that won't move. The rear shock tower doesn't have this issue. The screws themselves are a bit worn, have some surface rust but aren't rounded. How do you loosen these?

edit: got a little help from my dad, we had to use more force, the previous owner probably tightened the ever living crap out of these mounting screws and said "eh, good enough"

 

[81exige]

Update: servo in. Servo used: this one. 37kg of torque (or so it's claimed) @ 6V at this price is really good value for something with tires this big.
Also gander at my amazing (not) wiring.

There is actually a problem with this setup but it may not be obvious. The servo linkage is actually snagging on the RX box. Maybe the servo arm that came with the car is too long?