Rally Truck - HPI RS4/MT2 hybrid

[monkeyracer]

Through the process of building my IFS Savvy Avvy and my MT2SC 4WD SC build, I realized I had almost enough spare parts to build yet another RS4 based vehicle.

I wanted something different than just another touring car or drifter, so I looked at what parts I had, and found an MT2 chassis (since the MT2SC got a new chassis) and RS4 suspension and driveline components. I only needed a couple minor pieces that I found on ebay, so I got to building.

After a few minutes of assembly, here's what I had:











I had to borrow the transmission from the MT2SC, but this will get it's own transmission (more ebay) very soon, which is just a trans from the MT2 (single speed with a slipper.)

The next issue was that I needed to find a body to fit the extended length chassis, since standard Touring Car bodies won't fit. Measured the wheelbase (11.7") and picked up a very inexpensive, barely used C10 body from the classifieds. This will be a temporary body though, I will look at some of the other similar wheelbase bodies to get a clear one to paint how I want.

Here's what it looks like with the body mounted:







The wheelbase is just slightly too long, but not really too bad.

Will probably try to get a clear SCX10 CF100 body (since everyone has one they will never use and I can pick one up cheap) or maybe an Axial rat rod body.

I'm heading out right now to go test out the gear ratio and the overall feel of the vehicle.

Comments, questions, suggestions?

[boza]

very interesting mod! I always wanted to put RS4 parts on MT2 to make a rally car of sort. Just wondering how much of the rs4 evo 3 will bolt onto the MT2 chassis? would it be possible?

[monkeyracer]

Originally Posted by boza

very interesting mod! I always wanted to put RS4 parts on MT2 to make a rally car of sort. Just wondering how much of the rs4 evo 3 will bolt onto the MT2 chassis? would it be possible?

That is exactly what I did, I used the mt2 chassis and transmission (and dogbones) everything else is from a RS4 evo 3. If you do that, post some pics up, I'd love to see them.

This thing is fun, I ran it on 3S through my sidewinder, and it took some VERY tough tumbles and cart wheels, and always landed on it's tires ready to roll again. I fried the sidewinder though, so I am going to make my drifter ESC/rx easy to swap between this vehicle and the drifter (both will run on 2S.)

Both my drill batteries died on me yesterday, so I have to go borrow a drill to make the esc/rx plate. More later...

[boza]

very interesting.... unfortunately I do not have a MT2 to rape parts from, which is why i was curious if a straight chassis transfer would work.

[monkeyracer]

Originally Posted by boza

very interesting.... unfortunately I do not have a MT2 to rape parts from, which is why i was curious if a straight chassis transfer would work.

If you have an RS4 Evo 3, you would just need to get the MT2 center dogbones, chassis, and upper deck (all fairly inexpensive on ebay). From there you would need to figure out where to mount the motor and electronics.

[monkeyracer]

Been a while with no update, but not much has happened to it since April.

I got a CF-100 body, and started to mask it off for the paint scheme, but just couldn't get the tape lines right, and it was taking WAY too long to get just one side of the tape done, so I scrapped the idea, and decided to go with an easier paint job. (Pics will come when I get the black laid down.)

Basically it's a simple fade paint job, something easy to lay down, but would look nice with some graphics (stickers) on top.

I sold the MT2SC that I borrowed the trans from so this has been sitting on my project shelf since April, but I am looking at a few trans options including just grabbing some spur gears and shafts and putting together something just to get it going.

So, will have paint pics probably tomorrow (or Sunday) and some updates very soon.

[sweli]

Very cool, "thinking out of the box" idea!

What lower arms are you using? ie - Evo 3 or other? What track (width) does it give you?

What about just a simple Pede trans turned sideways? You would need to gear it up some or run it on 3s with a faster motor.


I have been thinking of using some RS4 lower arms, carriers and knuckles for an IFS rig.
I have a different dif I am thinking of using, but am not sure if the RS4 universal shafts will fit the output cups.
Can you tell me the diameter of the inner CV balls on the driveshafts?
Are you using CVs, CVD's or Universals on yours? Do the feel strong enough to take some 1.9 scaler abuse?

Post back and let us know how it runs.

[monkeyracer]

Originally Posted by sweli

Very cool, "thinking out of the box" idea!

Thanks! I've actually had this in my head for a while, it just came together with the right spare parts (and a very few custom parts)

Originally Posted by sweli

What lower arms are you using? ie - Evo 3 or other? What track (width) does it give you?

Evo 3. Really the only parts that aren't evo 3 are the chassis and center dogbones.

With HPI aluminum hexes and standard touring car wheels, I am at about 7 3/4" outside of the tires. The rear has spacers on the hex so that the wheels clear the chassis, so they are about another 1/4 wider.

For my Savvy Avvy build, I modified the lower arms so that the width ends up exactly the same as Axial axles hex to hex, but it was a lot of work to find the right dogbones and if I had to do it again, I would not have done it that way.

Originally Posted by sweli

What about just a simple Pede trans turned sideways? You would need to gear it up some or run it on 3s with a faster motor.

I'm going to end up just using the RS4 trans (I ordered one) and I've got a heat sink/motor mount that will work out perfect for this.
The pede trans would work fine, but I'm not sure on gearing. If it's too low, go with a large pinion or a small spur, etc.

Originally Posted by sweli

I have been thinking of using some RS4 lower arms, carriers and knuckles for an IFS rig.
I have a different dif I am thinking of using, but am not sure if the RS4 universal shafts will fit the output cups.

Can you tell me the diameter of the inner CV balls on the driveshafts?
Are you using CVs, CVD's or Universals on yours? Do the feel strong enough to take some 1.9 scaler abuse?

Post back and let us know how it runs.

My Savvy Avvy uses the RS4 front end, but with an Axial differential and locker. The dog bone cups are the heavy duty ones from the MT2, and have a bigger dogbone ball (7mm) than the standard ball (6mm).

On the rally truck I am using the standard dogbones. I bent one set because I let the arms travel beyond what they should and the bone got caught in the cup slot. Since I've limited the travel, I've had no problems with it.

For the Savvy Avvy, I've got some duratrax bones, but I haven't driven it yet, (a lot of custom work and low on my project list) so i don't know if they will hold up.

For a scaler, I would recommend the CVDs, especially if you plan to compete with it. The rally truck is a basher, and the avvy will be mostly for trail runs and fun, so it's not a big deal to me.

[monkeyracer]

Body mounted:









Still need to get the drivetrain figured out. I got an MT2 transmission, but need the spur gear and shaft still. Although, I am starting to think it might be easier to just make my own out of Delrin. Also need to redo the upper chassis plate after I figure out the trans.
Also need to find some headlight buckets and smooth out the wheel wells, but I'm really close to getting this thing done.

[clayton78]

Wow! That would be a awsome new class to run!!!!

[monkeyracer]

Hopefully this inspires someone to build something like this. It's actually a pretty easy swap. The tough thing is getting an upper chassis, and figuring out body mounts and battery placement. The truck bodies are easy to get too.

I probably wouldn't compete with this, since I built this for fun, but I could see these compete on the same tracks as the rally cars...

[monkeyracer]

Wow, it's been awhile since I updated this...

I got everything together and ready to go. I can finally claim this build as done.

Here's some pics of the updates:









I took it for a test run, and the motor got a little too hot, so I reset the gear mesh, hopefully that will help. Here's a pic of it on the nearby track:


(By the way, I love the camera on the Samsung Galaxy SII...)

May look into a brushless system, but I want to see how this set-up performs.
Only thing left is to get some lights on it.

[meatmonkey]

Nice build. Definately different.

What was required to mount the electric motor to the Nitro RS4 chassis?

And does it have enough travel for jumps?

[Knytemare]

That looks really cool! I have an old RTR3 chassis sitting around too, and yes, what did you use to mount the motor?

[monkeyracer]

Really it is easier than I thought it would be. I just grabbed one of these:

Motor mount(AL6061)

and a 1/8 - 5mm pinion adapter and Mod1 pinion and that's it.

The motor mount back holes go in the front most engine mount holes, and the front holes had to be drilled into the plate.

The tough part was battery placement. The battery I am using is just a 1300mAh 3S Lipo.

I realized though that I need to flip the spur around so the slipper is on the front side so I can push the motor back a little.

As far as suspension travel, it's got enough for the types of tracks/terrain this will see. I've taken it off speed bumps and short jumps, but nothing short course trucks see. I do want to get better shocks for it though.

[Knytemare]

Do you think the motor mount will go in the normal slots for an engine with the spur gear placed correctly?

[monkeyracer]

When I flip the spur and move the motor back, I will take some pics of the underside of the chassis to show where it mounts.

The stock nitro engine mounts are too far back unless you get a 3674 sized brushless motor.