Grom Brushless 3s / 4s Granite Grom Build (Pricey Build)

[Hellamass]

So I love the lil Grom but I just had to do it a solid. I cut the front springs by 1.5 loops, removed all shock spacers, added 40w oil in the rears, jammed a 4100kv brushless motor and Mamba ESC combo from Castle, added AVC receiver, new dx3 remote, 3s / 4s lipo, and kept the gearing the same ratio. Holy sheet does this thing move now! Handling is very solid as well. See pics below for the parts you’ll need.

And yes the parts cost more than the car . I did this just for the fun of it.

12/1/2023 Update - The 15 tooth gear is actually incorrect in this picture. Be sure use a 16 tooth pinion (Not pictured with 0.5 mod cut gears, and shaft size of 2mm when using the Castle motor pictured. If you want different gearing you will need to order the motor mount kit ARA320744 (not pictured) from Arrma which will allow you to adjust motor mesh for different gearing. Do not that your manual does go over what motor mount is required for various gears.

Parts list:

- Battery: Spektrum 3s 1300 mah smart (You can go with 4s well but not recommended)
- ESC and battery connectors: Spektrum IC3 SPMXCA303
- Charger: Spektrum S120 smart charger (any 3s charger will do) SPMXC1020
- Motor mount: Arrma ARA320744 (allows an array of gearing. Not required if you stay with 16t gearing. OE gear is 16t but 2.3 mm shaft which will not work here.)
- Alternative motor mount GPM aluminum on the way: GPM MGG018
- Servo + ESC x2 mount: you will also a 2nd servo mount to be drill into your drive shaft cover and screw in a second servo mount which will reach over the battery tray for a second mount spot for your esc or receiver. ARA320753
- Motor + ESC combo: 0808 motor and Castle Mamba X2 micro esc. This is really overkill on power.
- Motor Extreme Overkill: Use the Castle 1007 6350kV which is great at the motor shaft is 3.175 aka 1/8" and wont break off. Product #: 060-0104-00
- Receiver: SPMSR 6200A (with AVC)
- Radio: Spektrum DX3 or DX5c. (with AVC)
- Pinion for Castle 0808: 16 or 18 tooth .05 mod 2mm shaft. Any brand will do but Losi seems to be the one I selected. LOS212054 or LOS212022
- Pinion for Castle 1007: 18 or 19 tooth .05 mod 3.175 aka 1/8 shaft. Only a few brands available here but do check out Hot racing CSG18M05 or 19t Part Number: L519 on ebay.
- Antenna mount: Losi LOS231071
- ARRMA Adjustable turn buckles: ARA340208 (Not recommended as thy snap easily)
- GPM turning links: MGG162-R (I like these as they are not adjustable and are strong)
- Aluminum center shaft: ARA311194
- Aluminum shocks: ARA330824
- Steel front and rear Diffs ARA311193 (Required) Do check the fluid when you get these as they tend to leak out. 3000 cst will do.
- Steel axles: ARA311198 (required)
- Hot Racing Wheelie bar in the rear
- Modified hot Racing wheelie bar by bending and removing wheels to create a front skid plate. (photos coming soon)
- GPM suspension arms all around: GPM MGG4567
- GPM aluminum axle hubs: GPM MGG2122
- GPM aluminum Steering set: GPM MGG048
- GPM Aluminum front diff cover GPM MGG012
- GMP Servo saver: You can get this is 25T for after market servo's MGG025TSH
- Hot Racing Servo Saver: Use this is you are keeping your original servo that has 20T. GRM48SH20T
- Surpass USA Aluminum Wheel Nuts - Found this on Ebay
- Custom painted body - ARA412004 and ARA320804. You will need a set of body clips if you don't reuse what you have
- Heat sink for 20mm can. - Mpi MAXX Products ACC3920 (photos coming soon)
- Alternative heat sink: 2030/2040/2435/2840 Motor Heat Sink with Fan. Found this on ebay. (photos coming soon)
- For the castle 1007 you can just reuse the ARMMA supplied heat sink and add a fan on top. 25mm Fan: ARA390290
- Double sided tape to hold the receiver, esc, On/Off switch in place. Do consider going with Velcro as it easier when maintaining the car and everything has to come out.
- 40W oil for rear shocks. Front is fine as is.
Wing: MJX Hyper Go RC 16210 Truggy Truck Rear Wing 1612A. this fits ok but not perfect. Alternatively you can wait until the typhon grom wing is released adn just mount that one.
- Consider getting plastic sliders for the roof hood and bed of the Grom.

I don't have a GPS so ill post a vid soon. Just know that its fast enough to flip if i yank on the gas at speed. I'd guess at least 55mph.

 

[Bustedaw11]

So I love the lil Grom but I just had to do it a solid. I cut the front springs by 1.5 loops, removed all shock spacers, added 40w oil in the rears, jammed a 4100kv brushless motor and esc combo from castle, added EVC receiver, new dx3 remote, 3s lipo, and kept the gearing the same ratio. Holy sheet does this thing move now! Handling is very solid as well. See pics below for the parts you’ll need. Note that I’m still awaiting my antenna tube.
And yes the parts cost more than the car . I did this just for the fun of it. View attachment 332418

View attachment 332417

Very nice!
I love my 0808 on 3s. Mines the 8200kv. Not sure itd pull a grom very well without creating a lot of heat though.

Looks like it was made for it

 

[MrTitanium]

How are the diffs holding up? I have concerns.

 

[Tex Koder]

Want to see a Video to witness how Fast it moves now...

 

[Rcproponent]

I’m tuned in for how the diffs hold up but I agree… looks like that was made to go in there haha

Really cool man!

 

[Hellamass]

Very nice!
I love my 0808 on 3s. Mines the 8200kv. Not sure itd pull a grom very well without creating a lot of heat though.

Looks like it was made for it

Yea this set up runs at about 140 degrees max in a 70 degree day. I used an ir heat gun to measure it. One annoying thing that I’m trying to work out is the constant beeps from the castle esc. Annoying.

How are the diffs holding up? I have concerns.

So far 2 full bash sessions with zero issues. I heavily lubricated everything as I had the same concerns. Session included countless full speed runs on pavement and grass, light jumps and about 50 roll overs. Top tip, put avc to 50 percent.

 

[Hellamass]

How are the diffs holding up? I have concerns.

I shredded my pinion several times and figured out that I installed the incorrect 16T vs the 16th tooth as needed. so the mesh wasn't quite perfect. Also figured out ARRMA has a kit for various size pinions. Im thinking I will try out 18T next which is a 10% hit on torque and increase on speed. Will need to measure motor temps.

I’m tuned in for how the diffs hold up but I agree… looks like that was made to go in there haha

Really cool man!

So far the diffs are doing fine. but the pinion was shredded due to my error. Needs to be 16t not 15t.

 

[Hellamass]

Heads up. I’ll be posting a speed run this weekend.

 

[RCbuzz]

Those plastic sun and satellite gears are taking the punishment eh?

 

[Hellamass]

Those plastic sun and satellite gears are taking the punishment eh?

Yea they sure are and they are quite noisy at this point. My plan this weekend is to give it a speed run on vid with gps and share it. Only parts I don’t have in yet are the steel diffs and aluminum shocks. Both are on back order.

 

[Ames]

Nice build. How is it holding up?

 

[Luke66]

4s??!!?!?!?!??!

 

[Hellamass]

4s??!!?!?!?!??!

I did it and it was pointless. Just more weight.

Nice build. How is it holding up?

The speed really takes a toll on the car. I tear it up pretty bad at speed but if i keep it below 40 MPH it test to survive more often.

 

[rag30]

So how did you mount the original servo back into the car?

 

[Deceased]

Do you recommend going with IC3 or EC3? I’m still debating on what option to go with.

 

[Hellamass]

Do you recommend going with IC3 or EC3? I’m still debating on what option to go with.

It’s the same really. Just a matter of deciding how many types of connectors you want to support across all your rc’s.

So how did you mount the original servo back into the car?

https://www.ebay.com/itm/2960130400...YfrLeITT6a&var=&widget_ver=artemis&media=COPY

Yea they sure are and they are quite noisy at this point. My plan this weekend is to give it a speed run on vid with gps and share it. Only parts I don’t have in yet are the steel diffs and aluminum shocks. Both are on back order.

I ran the exact same gearing and electronics in my typhon grom and hit 70mph.

 

[Deceased]

It’s the same really. Just a matter of deciding how many types of connectors you want to support across all your rc’s.

It doesn’t matter if I want to run 4s on it? It wouldn’t damage the connectors it should be fine right?

 

[danny1202]

That’s an awesome little build.

I love the paint job

 

[H1-ROADBLOK]

What paint did you use to do the black pen stripping? The paint job is:

 

[Hellamass]

It doesn’t matter if I want to run 4s on it? It wouldn’t damage the connectors it should be fine right?

It won’t matter as the ESC are pretty small and max out at about 60 amps you will be good. I use xt60 with zero issues. Connectors don’t even get hot but do buy high quality connectors and you want low electrical resistance. Resistance equals heat equals power loss.

It won’t matter as the ESC are pretty small and max out at about 60 amps you will be good. I use xt60 with zero issues. Connectors don’t even get hot but do buy high quality connectors and you want low electrical resistance. Resistance equals heat equals power loss.

Same goes for ec3 or ic3. Works fine.