DIY RC Street Racing Car: One Week Classroom Project

by Banana_Science Feb 13, 2018
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I noticed the rear driven gear would strip after even one run - motor torque on the drive gear is awesome.

You will have to do some scaling of the driven gear to ensure good meshing. Another option is to make the upper motor mounting hole a slot so gear engagement can be adjusted.
I scaled up my gear 103.5% and got good engagement, but the length of the gear was less than the length of the drive gear. Since there was room, I first beefed up the gear by making it wider so that in all cases it would mesh with the drive gear. That helped, but that instant torque could strip the gear in seconds.
So I played around, and I ended up with a 3-piece design. I wanted to absorb the torque shock on the teeth so I could run it for more than a couple of minutes!
I made a three piece unit - center hub in PETG or PLA, outer gear in PETG or PLA, and the body of the gear in PU Flex. Seems to hold up much better.
I have a dual head printer and printed all at once, but it does not turn out as well as printing the items separate and pressing together. Also, if the outer gear is damaged or stripped, simply pop off the old one and press on a spare - see pic of the first one made - a little rough but works.

Hmmm... what pinion gear are you using? Some other pinion gears with the same 2mm 14t spec can be a different diameter and cause the rear drive gear to strip easily. We've designed this car around the pinion gear linked in the description so that we've never had to replace a rear drive gear at all. If you want, you can easily change the tooth count, diameter, and more of our rear drive gear to make it fit better by simply changing a few variables in our public Onshape document. Nice job coming up with that nifty fix though ;) Hope this helps!

I ordered the pinion on the list. Regardless, the gear tooth size is small enough that .1-.2 mm variation in center to center distance (3d printer variance) would reduce engagement. My first gear stripped before the car traveled one foot; this prompted me to look closer.

Just sayin’. Some adjustment might help some builders. I noticed you mentioned having extra gears printed for the class since they do wear out after a while.

This project has been fun!

That's good to know! Thanks for the advice. We have just uploaded 6 other gears of slightly differing tooth counts to make it fit better for different printer tolerances.

Makes sense. Change the tooth count and change the pitch circle.

Do you have better durability with the PLA or PETG.

I haven't tried PETG yet but I've been running the same PLA gear for the past four months (like 50 batteries). PETG is definitely worth a try though.

Hi. This thing looks frickin amazing! I need to give my dad a list of the parts and the prices so I was wondering what the quantity of the non printed parts. Are they all one each?

Thanks! For most of the non 3D printed parts besides the bolts and nuts, you only need one.

I'm having trouble sourcing some of these parts in Canada. The one motor I found was this: https://www.amazon.ca/abcGoodefg-Brushless-Accessories-Quadcopter-Helicopter/dp/B07D546LXK/ref=sr_1_3?ie=UTF8&qid=1533097136&sr=8-3&keywords=rc+motor+with+esc

Would this work? I've also had a hard time finding the pinion gear in Canada, are there any alternatives?

Hey, sorry for my late response, I read your message and forgot to respond. I don't think that motor will work unless you do some gnarly modifications. I would get this motor instead. The key thing is to get a 2430 7200KV 4P brushles motor since that is the motor the car was designed to fit. I'm not sure what parts are available or not in Canada so I'm not sure how much of a help I could be in that regard. If you have a question whether or not a part will work or not, feel free to contact me and check though. A lot of other people are also having trouble sourcing the pinion gear since they seem to be out of stock but I think another Thingiverse user designed a 3D printable pinion gear and posted their .STL in the comments here somewhere...

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Thanks so much for this project... I love that is has both CNC and 3D printed parts. I have the car built and for the most part working and have learned a ton along the way. I am having an issue with the pinion gear and the drive gear that I was hoping to get some advice and/or a suggestion on how to fix. The pinion gear and drive gear don't touch. To make contact I put a shim in to pivot the pinion gear toward the drive gear, which works but tears up the main gear. I am wondering if I purchased the wrong pinion gear (https://www.amazon.com/gp/product/B000BQ5AYY/ref=oh_aui_detailpage_o07_s00?ie=UTF8&psc=1) or if this issue has been seen by others? I feel my options would be to make a slightly larger main gear or try to drill out the mounting holes and move the motor back towards the drive gear. Is the source file for the main gear available for me to make modifications? Also if I opted to drill out the mounting holes will the screws be able to hold the motor in place, or will they most likely slip?

Again, great project!

Yeah it looks like you might be running the wrong size of pinion gear. I would get the one from Hobbyking when they come back in stock as that was the one we designed the car around. If you want to make some super easy changes to the 3D printed gear to make it fit your current pinion gear, just change the tooth count variable in the gear part studio within our Onshape document and everything should reconfigure itself. I would not recommend moving the motor or jerry rigging any motor mounting solution because even the slightest bit of slip on either gear will cause them to totally shred into nothingness. Just change the tooth count and print a slightly larger rear gear.

We also happen to have a crap ton of motors, pinion gears, and ESCs left over from the 2017 Inventing Reality Summer Program which we would be happy to ship to you if they would be of any use. You just gotta pay postage. We just have no need for 12 extra cars ;)

Hi there, I would love to get some of these parts from you if you have some available still. Having a hard time finding the pinion gear and motor in Canada.

I got the wrong pinion gear as well, so I would definitely pay postage as well as be willing to make a donation to your program for future projects you do if you're willing to send some parts! I will send you a direct message regarding this.

However, I also wanted to confirm the STL for the bottom plate that's posted is the updated version for 3d printing, correct? I wanted to print a new one with correctly sized holes.

Yup the STL labeled for 3D printing can be printed with the slightly larger holes.

Thank you for this thing! Thumbs up to you!

I've finished printing everything in resin, thought you might be interested in a picture of all the parts pre-assembly. They still need a small amount of sanding to get rid of some of the bumps left over from supports, but they're ready otherwise.


There are so many design flaws with this. There are no assembly instructions, so I had to just figure it out on my own. The sides don't fit properly into the baseplate, so I had to drill the holes to make them bigger. And when I finally finished building it, it stoped working after about 15 seconds. The smaller gear was so stripped and utterly destroyed that you couldn't even tell what it was supposed to be anymore. The only reason I'm still trying with this is that it still looks like a lot of fun to drive.

Sorry to hear that! Did you 3D print the bottom plate? It's sized so that it needs to be laser cut or the fittings will be very tight. I'll work on a 3D printed version tonight to fix that though. I'm not sure what happened with the rear gear though. I would check that everything is tight and you are using the right size pinion gear. If even one of the motor screws are lose, the rear gear will grind down quickly. I've owned my version of this car for over six months and have only had to replace the steering servo a few times after hard crashes. Additionally, we guided almost 20 6-12 graders to build these thing last summer and never had any problems with the fittings or gears over the course of the week. What filament are you printing with? The tolerances on this car are such that it's ideal to print in PLA.

I 3D printed the bottom plate. I did figure out the problem with the gear though. It was on but not quite all the way, so it was only barely touching the other gear. Guess I'll just have to shove it on harder. Yes, I am using PLA. I guess I was just a little irritated when I posted that, but now I've calmed down and fixed most of the problems. To be honest, it was a little fun figuring out how to build the car on my own instead of using instructions.

One other question though. How long is the battery supposed to last? Should I charge it after every use, or just once in a while?

XD Glad it worked out. I know how frustrating a poorly put together tutorial can be especially after you spent $65 on parts! Really sorry about that. Hopefully my updated bottom plate should help. Sorry for not thinking of that earlier and uploading a modified design for 3D printing. With an 850mah 2s it should drive for like 15-20 minutes of continuous driving based on my very limited testing. I would charge it every time...

Okay so I just updated the bottom plate so that it should fit when 3D printed without having to drill out any holes. I hope this helps!

Oh no! I had just finished 3d printing the bottom plate in tough resin! I hope I can easily fix the holes

nooooooooooooooooo!! Resin is so expensive as well! Sorry about that!

I'm going to try to still use the one I already printed since it looks really nice - What modifications need to be made? Do the holes just need to be a little wider?

All you will have to do is drill out a few of the holes. The holes should only be .5mm too small so you might just be able to self-tap the screws in and avoid drilling all together.

This is awesome, thanks for posting this. My daughter and I have been going through the onshape tutorials to design the parts there are tutorials for and we've started printing and almost have everything printed, so we'll start building soon. I think I didn't print enough of some of the pre-designed smaller parts, though. There's the list in the main details of the 3d printed parts, but I don't see a quantity of how many you need for some of them. Is there a consolidated list somewhere?

I also took a slightly different approach and have only printed one part in PLA (the ruler). Everything else has been printed in a form2 SLA printer in durable, tough, and flexible resins.

Wow! It’s good to see somebody using our tutorials again! Sorry for not including the quantity of parts required I’ll add hat in tonight when I get back home. It’s going to look super clean after being printed on a Form2 compared to just an FDM.

Thanks, I appreciate it! I also saw a tutorial in the folder for the micro quad copter - we were going to try that next! I was new to OnShape and my daughter is pretty young, so it was a learning curve, but she got the hang of it. She enjoys TinkerCAD a bit more since it's easier and colorful. I saw some of the items in the "Project Ideas" for TinkerCAD in your Drive share, but didn't see associated tutorials like the OnShape ones. If you have any and willing to share, I'd love to see them. Thanks for sharing those, they are great!

We have three other projects we taught at the Inventing Reality camp including: brushed micro quadcopters, fully 3D printed model rockets, and compressed air marshmallow blasters. We’ve been really busy recently but will try to make an effort to list the remaining three projects on Thingiverse ASAP. I’m not sure if we also shared our tinkercad slide decks as well but we also have a few tutorials on the basics of tinkercad as well. Thanks!!!!!!!!

Hi there. Any chance you could help us with the wiring the jst connector to battery. I have built the car but no idea what wires to cut to plug into other wires. I cant see any details in your photos. Any help here would be appreciated. Thanks

Sure! Sorry for not including any wiring photos. Here's a photo of how all the wiring should look outside the car. Just let us know if you need any more details!

How do you power the receiver? from the ESC? or you need a connection to the battery?

Actually scrap that last comment. I figured it out. I bought the battery from amazon and it came with a XT30 plug so I need to get an XT30 female for the ESC I believe.

Yup an xt30 would work great

That helps us a lot thank you. The battery in the photo looks different to the one you link to. Is the photo above a T connector connected to the ESC, because that's what connector comes with the battery already. In your instructions you say to change it for a JST socket. I'm still a little confused. So I potentially need to buy a T connector for the ESC not a JST connector perhaps ?

Sorry I just haven't converted those connectors yet in the photo. That battery in the photo is also not the correct battery. I just used it in the photo because I couldn't find the correct one ;)

The total cost of non 3D printed parts including everything such as bolts, nuts, and connectors is $62.74.

Ok thanks for the reply , and awesome job you and your students did :)

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hey , will the engine mount except any other type of motor (size) ? Ty

I'm not sure. I've only tried one size but it would be relatively easy to update the design to fit a different motor.


What temp settings did you use for the printing of the Ninja flex ?

Whats the total cost of all the non 3d printed parts and about how many printing hours does it take?

The cost of non 3D printed parts including everything such as bolts, nuts, and connectors is $62.74. I never thought to time the printing but if you were to do the hybrid TPU/PLA wheels it would probably be around 50 hours

Very simple design and well explained in words and pictures. I am trying to learn how to build something like this and your post helps a lot. Thank you.

Why didnt you pick the GT2B remote. That one has work really well for small projects like this. Especially for electric skateboards. It's cheaper too. Just wondering?

This remote just happened to be a little cheaper I guess.

Awesome, i wonder if a lower KV motor may be better looking at the traction and speed.

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Definitely. The car suffers from an overpowered motor and poor traction due to its light weight. It works really well on old, roughed up asphalt though with the current setup.

Can you please comment on both front and rear axles how many nuts, where they are located and what type? I think i've figured out the rear axle but just want to check. Trying to figure out front now.


Sorry about not making it more clear. Here are some screenshots from our Onshape design. If these screenshots aren't enough, you can easily copy our document and orbit/pan/delete parts of it to see how it all fits together. Just let us know if you want an exploded image of the rear axle.

Awesome, thanks!! My bearings should be arriving today so i'll be able to assemble the car! I'll post some pictures when i'm finished!

Do you have any video for it? Looking forward to make it with my grand kids. Thank you for sharing.

I just finished a quick driving video: https://youtu.be/rkeiZ0WCqgk Sorry it took so long (lots of homework)!

Looking good. I made 2 of them already. The only difference from your original build:

  1. 3D printed all parts (no laser cut).
  2. Motor pinion gear is out of stock, made 3D printed with set screw- working great, can provide .STL file if needed.

Can you post pinion gear stl??
Thanks :)

Awesome, Thanks!! What size set screw did you use?

i used 3mm x 5mm regular screw

Thanks for that file! Mind if I upload it this listing and credit you in the description?

No problem at all.

Wow! A 3D printed pinion gear! If you could post an .STL that would be great! I know those gears are always out of stock and it would help a TON of people if they could just print their own. I'm glad you like the design!

I don't have an official video yet, but I'll film a quick something this afternoon for you.

Great, Thank you! I started printing plastic parts. Will post some pictures when it done.

Sorry, but I ran out of time this weekend. I'll try my best to get something quick filmed ASAP.