Mojave Grom 4S Speedrun Conversion

[floe]

Hi there

On the list of stupid things to do in RC, trying to make a Mojave Grom go very fast must be pretty high up there It's basically a small brick on wheels topped of with an open cockpit and soft off-road suspension. That must be reason enough to try it out, and so be it.

The project is still in its initial phase and so far I have only sourced the motor, ESC, a receiver with build in gyro, some foam tires and upgraded diff covers. I have a rear diffuser inbound and looking for a front splitter as well. The cockpit will be closed off by lexan windows.

A buddy of mine is making CFD simulations and working with aerodynamics so I'll get some help from him as well. Wish me luck

 

[WickedFog]

Looking forward to this one. Great looking truck!

 

[ahr43]

With enough power, even a small brick can go fast. Reads like you're including aero from the get-go. Smart. Good luck and post up progress and images as you go. -AC

 

[9x19]

With enough power, even a small brick can go fast. Reads like you're including aero from the get-go. Smart. Good luck and post up progress and images as you go. -AC

As the F4 Phantom proved...

Good luck with the endeavor!

 

[Doom!]

Good Luck! Have fun, sometime you need a good challenge.

 

[CertifiedMike]

Don't forget to install a parachute!!!

 

[floe]

So the stock BLX differentials come with 3.000 cst oil in them. I expect this to be way to thin for a speedrun build, but how thick should I go?

I am thinking about 30k but I am really not sure. Anyone have any ideas about this?

 

[CertifiedMike]

So the stock BLX differentials come with 3.000 cst oil in them. I expect this to be way to thin for a speedrun build, but how thick should I go?

I am thinking about 30k but I am really not sure. Anyone have any ideas about this?

I think you're on the right track. Getting the diffs close to 'locked' is going to help in speed runs.
There are some Arrma speed run builds that could get you pointed in the right direction.
Each build will be unique but a lot of Arrma cars use similar designs and parts.
I'm excited to see if you make this all work!!!
I'm not sure I've seen a Grom speed build yet!

 

[floe]

Exactly. A limitless speed run build would be 1M in diffs. Of course it's a lot bigger so I probably won't need to go that high

I've seen a few but it has always been the Typhon which quite frankly is much more suited to a speed run build. That's exactly why I want to go with the Mojave. I'm trying to keep it as stock looking as possible

 

[floe]

Been spending an hour trying to mold the front window in lexan by hand. Jeez it's not easy but I think I'm getting there...

 

[Doom!]

I don't know if the would fit but tearoff's for motorcycle goggles would probably work great and are very flexible. Of course now that you've done most of the work this probably doesn't help much.

The ones I linked are 12"x4" incase you decide to try it.

 

[floe]

So far so good. Windscreen glued. Next up side Windows

 

[floe]

Received and installed a GPM aluminium steering rack. Need that little rocket to point in a straight line

 

[floe]

I present... The world's first Mojave Grom to feature windows This was so much harder than I thought. Molded the windows by hand in 0.8mm lexan and glued them to the body from the inside using Shoe Goo. Was a nightmare to get the fitment right and afterwards to get the body to fit to the interior. It's not perfect but it's not bad either.

Lowered the vehicle 10mm both front and rear. Probably have to raise the rear a bit to achieve a rake.

 

[floe]

Got the diffuser installed. It's from the Nascar Grom and is a perfect fit to the Mojave body. Was not easy to source here in Europe - we have not got the Nascar.

Ideally I would like to try the front splitter from the Nascar as well but it is back ordered everywhere Guess I have to make my own then

 

[floe]

Mounted a new high speed high torque servo running 8.4V, an aluminium servo mount and servo saver delete. Slowly getting there

 

[floe]

The stock differentials are "filled" with a thin 3000 cst silicone oil. In typical Arrma fashion filled means they put like two drops of oil in them. I disassembled both front and rear diff and filled them to the top with 100k cst oil to lock up the diffs more than stock. They were extremely loose before but now they are nice and tight.

Almost cute those small diffs

Also raised the back of the car 4mm again to achieve a rake.

Now I just need to figure out how to put a front splitter on the rig and then it's time to send it

 

[floe]

So I finally got to drive the car for its maiden run today. I've been waiting for dry tarmac for ages now My aim was 100 kph / 62 mph isch which should be around what to expect using the stock gearing and the 4400 kv motor. Incredibly all went well. Crashed it under braking but no damage what so ever.

I am very pleased with the initial result. Now it's time to gear up!

 

[PaPa K]

Nice job on the build, looking forward to your progress.

 

[floe]

Nice job on the build, looking forward to your progress.

Thanks!

Stock pinion is 22T. I currently have a 24T, 26T and 28T to try out. Lets see for how long it is in one piece