MT4 G3 / ST1 Pro Bash Truggy conversion

[Lizard]

Hi,

wanted to share my not-yet-finished Thundertiger MT4 G3 Bash Truggy Conversion.

Well, generally the MT4 G3 seems to be a decent car, however I did not like a few things: The plastic cage is way too small, it won't allow for larger 6s packs or larger motors. Even if I managed to stuff in 6s there, the center of gravity would probably be too far to the right of the car. Also, the whole chassis is not really stiff. I didn't want to add a "Harley" Top Brace, that's too heavy, too ugly and the center of gravity gets elevated too much.

So I removed the plastic cage completely and changed the layout.

Used some angular plastic and made some chassis enclosures and batterypack holders. For stability, I added the chassis braces from the TT ST-1 Pro. Good thing is, my construction weighs about the same (250gram) as the stock plastic cage. Gives a more rigid car now with better weight distribution but still stock weight.

For motor/ESC I'll be using a Castle 1717 + MMM extreme from an XO-1. To make the 1717 fit the engine holder I had to open up the holes for the engine screws to 4mm and put 2mm Aluminum underneath for chassis clearance.

The center diff is composed of Savage 7075 Nova Diff-Housings, Nitro-Diff-Mod (little blocks on crosspins, like in newer Savage diffs), Savage spider gears, Kyosho 46t steel spur and Kyosho outdrive cups.
For Motor pinion I haven't decided yet, there is enough space to mount something between 17 and 22, so I'll have enough options.

The Body I will be using is from a Savage Flux, it fits pefectly in front of the Spoiler with it's flat truck bed. In addition to the Spoiler I mounted the MT4 G3 wheelybar.

I haven't decided yet on the layout of the front, maybe I'll put the steering servo to the left side, this way I have lots of space on the right side for a receiver box.

[CerberusVI]

Looks good, I want to see some vids when you get it all done with the 1717 combo in there! I almost jumped on the MT4-G3 band wagon when they 1st came out, but instead i built a Mugen Mbx5t. Still tempting to make it more into a Monster truggy like the G3

[Lizard]

I almost jumped on the MT4-G3 band wagon when they 1st came out

hehe, "bandwagen" that describes it well. Couldn't really understand why that MT4 G3 got hyped so much. I mean, it's a nice car, but not indestructible, like everybody says. I only got it because it was cheap and I already have a ST-1 Pro, this way I have a nice truggy for bashing with lots of spare parts.

Well, yesterday I finished the diff top-plate prototype made from acrylic glass. I will redo it later with alloy or carbon fiber.

Also weighed everything, final weight with 6s 5300mAh packs will probably be around 5.4 kg (12lbs). Castle 1717 motor with Savage diff is about 200grams heavier than stock motor.

[CerberusVI]

Looks good! i took my Mbx5t out with some 40 series road rages with a castle 1515 on 6s geared for around 64. I think that's around the fastest i've run any of my kits. What kinda speeds are you going for in your setup?

I don't want to say im a hater of the Mt4-G3 but i hate seeing all the OMFG its the BEST BASHER EVUR! When in reality it has weaknesses just like any other rc. It's probably a really good kit, the price point for a rtr is good, but in my eyes it's not the end all be all. I have to stay away from RCU and the wonder tiger forums now because of all the favoritism, loyalty and one sided assumptions about other kits.

Anywho...I like how your going outside the box with this build and not the normal brace the chassis, buy a bunch of digi-dem parts, buy better hinge pins, add a summit bumper stuff

[Lizard]

I'm not sure yet on the gearing, I hope I can use the 46/22 combo without the motor getting too hot.

46/22 with 6s and 3.7v per cell would calculate to 70mph (without tire balooning factored in).

[Lizard]

Well, the car is almost done.

The steering servo posts are the original ones I cut out of the MT4 G3 plastic cage. RC Box is from a Traxxas XO-1.
The ESC is mounted to the chassis plate as on the XO-1, but I'm not really happy with all that plastic, I think I will put everything in some Epoxy later.

Weight with 6s 5300mah battery, Body and HPI Phaltlines is 5303g, with Traxxas XO-1 wheels 4879g.

Gearing is 46/21, with XO-1 wheels and 6s with 3.7V that's 80km/h or 102km/h with Phaltlines.

Did a testrun yesterday, well, what can I say, the wheels take 0.5 seconds to accelerate from zero to 50mph, just the car has problems keeping up with that . Total driftmachine, but drives very well and controllable.

Motor was about 60 degress celsius after 15 minutes, I need to put a fan on it ...

[Lizard]

Took it out for a run on a big grass area yesterday, this time with Badlands and geared for 108 km/h (67 mph).

Seems like 500.000 cps diff fluid is not enough, front tires still try to baloon, could not reach topspeed because of that.
The center diff also got quite hot, I think I will replace it with a CEN limited slip diff and maybe put thicker fluid in it.

Apart from that, it was real fun, a Castle 1717 in a Truggy is definitely recommended.

[Lizard]

1/8 scale tires only last 10-20 packs for me, so got myself some 1/5 scale tires.


1) From a Carson Dirtattack 1/5 scale buggy.
They are already glued and with 280g reasably lightweight. Foams are soft enough for the 5-6Kg of an 1/8 scale car. Diameter is a little bigger than Maxx size but smaller than HPI GT2 tires, I really like it that way. What's not so nice is, that they have very little offset, so I needed wider squares. Took 17mm wide ones, vehicle width seems okay now. They seem quite sturdy, rubber is thicker also. I hope they'll hold up better than 1/8 tires that I always shred within 10 to 20 packs or so.

2) Carson FG wheels and FG Marder Buggy tires. Problem with them is, that the foam is too hard for 1/8 scale vehicles, but I have already ordered some softer ones. I also decided to turn down the part of the wheel where the tires are glued to (see pictures) because with softer foams I think the tire would "bottom out", not good. With FG foams and turned down wheels they only weigh 250gram now, nice.

3) PMT Supreme V2 touringcar onroad tires. Very good traction (wheelies with those small tires, yeah) but foams are a little to hard for 1/8 scale weight, I think I need to get some unglued ones and replace foams.


Center diff is still the Savage Nova diff, but with 2.000.000 cst Oil in it. I am almost not able to turn the diff by hand now :). If I grab the car by the rear wheels and push it over the ground with the front wheels the tires will skid, only if I press the car to the ground in a 45 degree angle the tires will move.
Driving was very good, all 4 tires now always have the same diameter, no front-balooning anymore. In general the tires baloon only very little. Interestingly, the center diff still got quite warm (but not hot anymore) so it's still doing it's job of protecting the drivetrain, very good.

Gearing was changed to 18/46, that's 97km/h with the Carson tires. Also fitted a small 50mm fan on the motor, temps are much better now, after running two packs, max temp was 47C, but most of the time it stayed around 37C. Ambient temp 20C.
But I must say, it feels a little slow now, it stops doing wheelis at about (estimated) 60-70km/h now, with the old gearing (108km/h) it would still do them at 80-90 estimated. Now it's somehow missing that nice "there's still plenty of oomph left" feeling at high speeds.

Seems like I have to improve motor cooling, so that I can run higher gearing again. Unfortunately I couldn't find a motormount that has good heat transfer to the chassis, seems like most manufacturers don't use their brain when designing motor mounts :(

[Lizard]

more pictures:

[Lizard]

Finally had the time and opportunity to make some videos. Sorry, they are a bit shaky.
I guess I smoked that guy with his yellow FG Monster Truck pretty good

Gearing was 20/46, topspeed 66mph measured with GPS "Android Tacho" app.


Offroad:
http://youtu.be/oJ4qirFzCLM

Onroad:
http://youtu.be/Gpb5UubZMMI

[Dr_T]

Hi Lizard!

I'm thinking of getting those PMT tires for my 8ight-T, to try and get a bit faster than those "baloon assisted" runs I did on the Reely tires. I really like the 120mm OD size, as 140+mm would only increase wheelying and 97mm is too small for my gearing options. Would you recommend them?

Ideally, I would want to try and mount them onto some standard (97mm dia?) truggy wheels to avoid the whole squares thing and to use softer foam inlays. Held a pair today in a LHS and they're really hard. You know if they're sold somehwere as tire only? Have you tried ungluing them for using softer foam inlays?

[Lizard]

Not sure if it's possible glueing them to a 1/8 Truggy rim, but I also searched for non-glued 1/5 touring car tires, couldn't find any, only 1/5 rain tires.

Ungluing them is probably not going to be easy, I won't do that anymore, did that years ago with 1/8 tires, tried both the acetone method and oven method, it's a mess and smells like hell.

If you put in softer foams, you'll probably also have to turn down those additional plastic parts of the rims like I did with the larger rims, otherwise bumps will probably "go through" the foams and hit the rim.

Here's what I mean:





On my 5.4Kg Truggy they didn't make much grip and didn't reach operating temperature, I guess the car was too light. Also the foams were a bit too hard like you already noticed. With the 8Kg Twin Truggy they are okay when they reach about 40-50 celsius. From what I've read in largescale forums, they need a 10Kg car and temps of 60-70 Celsius to get real sticky like glue.

Maybe try the new GRP 1/5 tires, they are supposed to be about 10% lighter than the PMTs and GRP claims their rubber compound doesn't rely on temperature. Not sure if that is true though.

[Dr_T]

Thanks! Yeah, might have to go with squares then. The new GRPs are actually under 60 EUR shipped from IT for 2 pair, that's not bad at all.

Being a total noob at this, what compound would you suggest, given the truck is about 5.4 kg like yours, the softest (S1 SuperSoft)? I like them to be grippy, but if that means wearing them out after a couple of runs, I'd settle for a bit less grip and a harder tire.

What compound are your PMTs and how did those wear on your truck? I've seen some softer ones being sold used on eBay and they typically look shredded.

EDIT.
Surface is likely to be that HSV Stadium Parkplatz in my video here, not even asphalt, but it'll do for now :D: https://www.youtube.com/watch?v=oxQXPdnsYAY

[Lizard]

I have the softest compound. Wear is okay with that, have run them a few packs on the Twin now and there's still a lot rubber left.

Not sure though how they perform on the surface you want to run them, I think they might be too hard for the surface and not run well. Like toktok-toktok-toktok :)

[Dr_T]

Yeah, surface is not ideal, but at least there is space to practice a bit. I haven't found a nice piece of empty asphalt yet here; for time being, I guess suspension has to stay soft and just work a bit harder.

Thanks for pointing me in the right direction. These 1/5 GT tire size and weight look perfect for trucks and truggies.