Mojave Choosing the right pinion gear aka dad I need to do a science project

[Summitp]

"Dad, I need help with my science project." I groaned when heard this. I knew he had to do one because he elected to skip the personal research project earlier in the year and now needs to do a science project. Due in a week. Ack.
K. So whaddya wanna do?
"Something with RC cars."
We decided to take a methodical approach to selecting the correct size pinion gear. The correct size being defined as the pinion gear that delivers the fastest top speed and maintains a stable motor temperature below 180f. It's cold out so we may lower that threshold a bit.
We designed an experiment and the Mojave is the guinea pig. Advanced speed detection technology is in hand (we found a sick lidar gun). We know a great spot where the road is smooth and straight and the traffic light.
Locktite has been applied to all the grub screws in our 11t-20t range of pinions. Wheel bearing have been replaced, and the body reinforced and a windshield added.
Tomorrow we see how fast this thing will go, hopefully without burning it up.

The car is a beat up, but relatively ship shape Mojave exb with proline badlands lp 3.8 tires and a castle 6s esc with a broken off fan and a 1515 2200kv motor.

Huh. Can't seem to add pics. Maybe I'll figure it out tomorrow.

This mojave

 

[Littlemotor]

Sounds good man! And hear ya go…..

 

[Summitp]

Yeah, it kept kicking out my photos from the body work I did tonight saying error, but the older pic of the truck worked fine.

 

[Littlemotor]

Hmmm, strange… Well the above top secret assistance is the extent of my knowledge lol..

 

[parcou]

"Dad, I need help with my science project." I groaned when heard this. I knew he had to do one because he elected to skip the personal research project earlier in the year and now needs to do a science project. Due in a week. Ack.
K. So whaddya wanna do?
"Something with RC cars."
We decided to take a methodical approach to selecting the correct size pinion gear. The correct size being defined as the pinion gear that delivers the fastest top speed and maintains a stable motor temperature below 180f. It's cold out so we may lower that threshold a bit.
We designed an experiment and the Mojave is the guinea pig. Advanced speed detection technology is in hand (we found a sick lidar gun). We know a great spot where the road is smooth and straight and the traffic light.
Locktite has been applied to all the grub screws in our 11t-20t range of pinions. Wheel bearing have been replaced, and the body reinforced and a windshield added.
Tomorrow we see how fast this thing will go, hopefully without burning it up.

The car is a beat up, but relatively ship shape Mojave exb with proline badlands lp 3.8 tires and a castle 6s esc with a broken off fan and a 1515 2200kv motor.

Huh. Can't seem to add pics. Maybe I'll figure it out tomorrow.

This mojave

View attachment 341106
View attachment 341105

I have a spreadsheet that I got from a YTer that I modified to get a paper estimate of RC speed when I change pinion based on tire size and battery 3S, 6S, etc. I never got a GPS to see how close I get based on my file. I would love to test it with GPS one day.

 

[Smilinbri]

Very cool science project. Better than building a volcano. Good luck and let us know how it turns out and what grade/feedback he gets on it.

 

[Summitp]

Yeah, it had been a while since I posted here to this forum. My photos need to be resized down to be able to upload.

We completed our testing today. It was frigid. That impacted our experiment. Furthermore, cheap ass Chinese crap pinion gear from Amazon are a waste of money. Luckily we were able to get runs in successfully with almost all the available gear ratios.
News to no one, (except maybe my kid) ideally this experiment should be run with a fully charged 6s packs that are consistent in how much voltage and current they can deliver. We also ran into issues with chinesium pinions failing.
Obviously, measurements taken in January when it's butt ass cold out with a storm moving in are not reflective of what one might expect to see in spring or summer.
But
I think the boy learned a ton about the scientific process. We saw diminishing speed returns as we increased the pinion size past 17. This aerodynamic brick with this motor and battery combo just did not want to push much last 60mph. Our max was 64.9 mph.
I have a couple pics at speed, but I haven't checked to see if they are any good yet.
Overall, pretty ime with the boy, and good to see his brain working. He is writing up enhancements to the experiment for the next time we run it.