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3D Printed RC Car V3 -- Tarmo3 -- Drivetrain [3/3]

by KrisCubed Apr 7, 2019
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Also, since I couldn't get that torque damper, so any suggestion for me if I want to redesign it?

What did you use to connect the servo with the steering?

I'm having issues with my axles snapping - within a minute of driving. Do you have any suggestions for me?
Here are my print settings:

  • I'm printing the axles lying on their sides - ball side down
  • 0.48 line thickness, 5 perimeters, 0.25 layer height
  • PLA printed at 205C
  • I'm using the modified torque damper using a clothespin.
  • And I'm using the recommended motor.
    Thank you

Unfortunately I can't guarantee the performance of the clothespin damper since I didn't design it and I haven't made one.\

Beyond that:

  1. how fast are you printing?--I print mine at 115-120 @60mm/s. Temp is only half the story since speed affects the behavior at each temp.
  2. Are you using the PTFE lube?--Just a light amount so it doesn't attract too much dust and dirt, but a little is needed.
  3. Are you 4wd or 2wd? --With 2wd the forces are nearly twice as much on the axle so they are more likely to break.
  4. What brand PLA are you using?--I found that some brands are MUCH stronger than others, I've been using ZIRO's Marble color PLA and its really good, I found that "AmazonBasics Premium PLA" is too soft and yields similar results to what your photos show.
  5. Are you using a locked or an open diff?--Again using a locked diff will cause the forces on the axles to go WAY up.

None of the things I've listed should be enough to cause the problem you've described. It's possible that its a combination of them? I am not sure. Sorry that I am not of more help than this--Its hard to know what is causing that without having the car in front of me. But that behavior is definitely abnormal.

Feel free to email me or continue this thread if none of those things salve the problem.

I wish I could find the spring to use your original torque damper...

  1. Print speeds, see image
  2. Yes, I am using the PTFE lube on all the gears, and on the axle joints.
  3. 4wd
  4. I've tried both AMZ3d as well as Prusament

I'll try some other filaments brands I have for the axles, and see if that helps.

I'd guess the problem is the damper. The spring I use is here: https://www.mcmaster.com/9271k419

I've tested the car without a damper and it normally drove for 3 or 4 minutes before the axles would break one by one. It's possible that the clothespin damper just doesn't work at all--But even still the car should last longer than you described. That's why I believe it is probably a combo of problems.

If mcmaster does not ship to your country you can always search other hardware sites for a spring of similar dimensions or check your local hardware store.

Hi Kris
Love your work.
Having a real close look at all the parts and assembling them in blender before I start the print.
I have noticed that there is a difference in the primary steering link .stl and the detail pictures.
Looks like the .stl is not really usable as uploaded and different from the link photographed.
Am I missing something or is the uploaded file an older version?

Keep up the great work, my son and I are really looking forward to building this.

I'm glad to hear it!!

Are you referring to the chanfer I added to the Main-Steering-Arm? I added that because the arm would collide with the upper control arm on the front suspension. I'm guessing that you're thinking that the rod end from the servo will have a hard time mounting to that screw hole that is on the chamfer--But as long as you use a 16mm screw or longer, there should be absolutely no problem.

Thanks for your quick response.
Yes, I was referring to Main-Steering-Arm, sorry, I didn't use the correct name.
I was concerned about the openings for both the Steering-Strut and Steering System Support parts,
but on closer inspection of the part i see the wall that i am concerned about seems to only be there for support of the upper chamfered layer of the part.
Am I correct in thinking that once printed, I would remove the "support wall" as indicated in my attachment?

Thanks again

Yes, I believe it is only one or two lines wide, you should be able to remove it with your finger no problem. If it doesn't work well, I can send you one without the support so your slicer can add its own supports.

hmm is there chance to reedesign motor mount, so that te gear would be mounted on the shaft? that would make finding motor easy,
not all outrunners have holes for bolts
i understand that current mounting is more realiable

sorry for my english im little rusty with it :)

I linked in the BOM what motor works best an an alternative. Unfortunately with plastic gears, mounting on the shaft doesn't work well since it can't be properly secured.

If you'd like to modify the parts to use the shaft anyway, here are the original files: http://www.bit.ly/tarmo3files

thank You Very much but i will try Youre design first, :)
can it be scaled up? like 10%?

I am not sure you can do that since parts like bearings would no longer fit. Tarmo4 will be ~12% larger though--But it won't be complete for some months.

Could You please make it all parts in one post/package?

That makes things confusing--Too many parts. There are only 3 pages. Links to each in description.

and another question do you put the gears on the motor? is it on the shaft? or not because its looks like its not on the shaft... im little confused

Yes you need to get the correct motor since it doesn't connect to the shaft, but the gear connects to the back of the body of the outrunner motor.

ok so another question, is there posibility to put a bigger motor ? like 540 brushless? or brushed? with matching esc ofcorse ?
Your desing is awsome but i wolud like a bigger more relible option for motor

A 540 will not fit--And as of now I do not recommend one. I am having trouble getting reliability from 540's right now. I've been testing one for use on Tarmo 4, but I am disappointed. Not enough torque. The outrunner has more torque than the 540's I've tested. that outrunner is really reliable.

thats something new
ok then outrunner

Hi Kris, first of all, congrats on the awesome design. I was looking to print another RC car (I already built the OpenRC F1) and decided to go for your Tarmo3 over the OpenRC Truggy as I found the sourced parts more readily available and the design looks more interesting.
Couple of questions:

  1. Have you noticed that the base of the Chassis_FRONTUPDATED is around 1.5 mm thicker than the Chassis--MID and Chassis--_REAR?
  2. Do you know if anyone has done an assembly guide?

I'm glad to hear it!

Yes, I know that it is thicker. It was revised after being published--The old one had the same thickness, but I made it thicker for a few reasons.
I am not aware of any guides--And I have not made one. I tried, but I am just far too busy between work and school (I'm currently taking summer classes).

I tried to post plenty of photos on each of the three pages to make it easy to see where each part fits--but if you get stuck, just message me on instagram or post to my subreddit and i will help you no problem.

I started the assembly based on the photos. So far so good. I almost finish printing it.
Do you know of any 3d printed wheels and tires?
I'd love to use something like this: https://www.thingiverse.com/thing:523776 and print it in flex like I did in with OpenRC F1.
BTW for anyone interested: Without the wheel end cups and wheel adapters, I have spent 667g of filament and 58h printing.

OpenRC 1:10 RC Truggy Rims AirLess
by 123CUT

Those should work I think. Try printing one and see if it fits!

Thanks for the info--I've printed the car several times but I've never taken care to record that information. I was hoping that it was less than one spool of filament.

Have you tried any alternative axle joint designs? I'm trying to use PETG and it's just not happening. :D

Yes, I've tested and continue to test many many axle designs--I have only printed PLA though. What is it doing? Are the axles not working well for you?

Part of the ball broke off for me, so I wanted to try a stronger material. The edges of the ball on the end is giving me trouble with PETG. It usually messes up a little and doesn't end up very spherical.

Couple of questions:

  1. What orientation are you printing the axles with?
  2. What is your line thickness and wall thickness and layer height?
  3. What is your print temp?
  4. are you using torque damper, does it have lubrication?
  5. Are you using recommended motor?

Found out my issue was from over extrusion. I reduced my flow by 5% and they're printing well now.

Hi mr. Kriscubed i wonder how to assemble the front diff.. can you help me? Thanks. And thanks for sharing your files...looking forward for your more project..

As I've no easy source for the torsion spring in the torque damper I set about designing another damper using a clothespin spring. I have no idea if it will work (still waiting for the final parts, especially the motor and servo, to arrive) but do you think it will work? I'm happy to send/post the files if you think it will be usefull.

A very interesting idea! But I suspect that it will be too stiff to do much. you can definitely try it though--You'll know if its working after about 10 minutes of driving.

Have received the last parts to get a rolling chassis and test drove it using a Hobywing ESC set to level 0 (the gentlest acceleration) for less than 10 minutes before i flipped it and it landed on a back wheel and snapped the top control arm from the hub bracket. No sign of other issues. Maybe i'll print a version without torquedamper and see if that makes a difference. I was first setting max speed to 25% which is already fast, 100% is crazy fast (that's when i made the mistake to take a slight turn at full speed and flipped the car ;-) )

Interesting, you must have really grippy wheels since I used to turn it like that at full speed and it would just slide lol--Was super fun to do that.

Also, I didn't see your photo before, that is an amazing design for the damper! Would you mind posting a remix?--For those who are interested in trying that.

There are people in parts of the world who message me that they can't get the correct spring because of import tariffs making it expensive to order things like that from overseas and there are no local sources--your design may help those people.

Remix submitted with my re-designed Torque Damper. https://www.thingiverse.com/thing:3709290

Torque Damper re-mix to use common clothes-pin spring

Can I ask what the torsion spring is for? Is it really necessary? Is it basically in place of a central differential between the front and rear drive shafts? Thanks for any info in advance

It removes torque spikes between the motor and the driveshafts. This keeps the CV-axles/dogbones from breaking.
It is needed---I didn't have it in the part files originally, but after more testing, I saw that the results I display in the youtube video are just not possible without that spring.

Does that make any sense? lol

Yes it does thanks for the info I got all the parts printed n looking forward to this build. I 've been driving the ursa monster truck for a while and love it but I found the central diff unnecessary which is why I asked about this before ordering the spring so thanks for the heads up and for providing the files so we can all have fun with it.

Definitely! Let me know if you need any information or assistance!

Hey so I was able to find a spring very close to the one you reccomended but on Amazon 10of em for $6 printed the parts dropped one in and it does make a difference so thanks again. I'm sitting here watching the YouTube vid and I noticed you had at one point positioned the servo vertically inside the chassis. Do you have the file for moving it to that position again. Id like to move mine like that so my truck body fits n looks better

Would you mind linking me to this amazon spring?--That'd be awesome because I tried searching for one there but I just couldn't find any.
Yes, that was an older design, but it should still fit the chassis I think. I can send it to you, but I don't want to post it here as it may cause confusion. DM me your email and I will send the part there.

Hi, I am making my way through the project and have run into a question. how did you connect the "Front_DiffCup-_Part_1" to the Traxxas differential gears? The the hold in the gears is to small for an m3 screw and the holes in the diff cup seem to large to thread an m3 into.
Thank You!

Many of those gears will come with a pin that you can use for that. if it didn't come with a pin, then you can use a tiny carter pin, or a heavy gauge wire and bend it so it won't come out, or even a paper clip will work.

Awesome, thank you!

So cool. Thank you for sharing this. I love everything you've done here, totally on my long term to-print-list.