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  • Cdub
    started a topic OpenSlotCar Design

    OpenSlotCar Design

    I've been working in starts and stops on a slot car design that maximizes what can be made with an inexpensive FDM style 3D printer.

    My goal is to give away the files and designs similar to Daniel Noree's OpenRC project (http://danielnoree.com/) , which I think is a great thing by the way. There's been several projects inspired by him, like the openRC Tractor project: http://makitpro.com/index.php/openrc-tractor/

    I have a hypothesis that there are a lot of schools and other organizations with FDM 3D printers that are not being used all that much. Filament is so cheap, that anything that is printed is basically free. So, if you can keep the cost to get the car running down to a couple bucks, I think you have a viable option to see a TON of slot cars get made.

    The beauty of slot cars is that so much of the cost of making the car run is tied into the track, and thus can be bought once and used with many different cars (with very little effort). Again, I'm comparing slot cars to RC cars.

    I've got one car built, that actually runs, although not very well. I tried running NinjaFlex tires, but they didn't provide much traction. I've been messing around with casting my own urethane tires, and they look and feel great, but I haven't had a chance to run them on the car.

    The first car I did was modeled after a 1974 Dodge Monaco. Not a traditional "race car" choice, but I had a bunch of normal Go!! racecars, and I love the Blues Brothers, so I started there.

    I need to shoot a little primer on the parts so they will photograph better (I printed them in bright yellow, because it was what I had laying around).

    So, the chassis, body, wheels, guide flag, and motor mount is all 3D printed in PLA. I used 1/8" drill rod for the axles as well as a little piece of it for the guide flag to pivot on.

    I had a bunch of king crowns laying around, so I used one. I think the final spec would be one of the generic crown gears, because they are so much cheaper.

    I've been experimenting with different motors. I have ordered more different motors than I've had time to test, but I've been focusing on inexpensive motors from ebay and banggood.

    Where I get really hung up is trying to model the bodies. I'm not so good at modelling the organic shapes. I have a few ideas on how to overcome this, but I want to get the first car working right first.

    Does anyone have any good references on scratch building a slot car controller? I'd like to come up with files and instructions to allow someone to make their own wirewound controller. Not necessarily because it saves money, but because it seems like it is difficult to consistently procure high quality controllers with the range of adjustment that you'd like to have for matching to a variety of cars. For example, when I was looking for controllers for my track, all I could really find were vintage AFX controllers. They are nice enough and a big upgrade over the stock controllers, but they feel like they will break pretty easily if they get dropped.

    So, that was a lot of words. I need to get some pictures together and start posting.

  • pfuetze
    replied
    Originally posted by Cdub View Post
    Thanks for posting the write up. It's been a while since I've looked at SCI. The new forum software seems pretty good.
    Did you end up using any of the lead weights or did you decide the car was faster without them?
    i did not use any of the lead weights.
    if the car is properly designed and built, on my track at least, you will not need any. this is a smooth wood track, things are different on segment plastic track.

    Leave a comment:


  • Cdub
    replied
    Thanks for posting the write up. It's been a while since I've looked at SCI. The new forum software seems pretty good.
    Did you end up using any of the lead weights or did you decide the car was faster without them?

    Leave a comment:


  • pfuetze
    replied


















    kit from OpenSlotCarDesign.
    runs really good, lap times under 10 seconds.
    files for printing will be available for download. body is nice, chassis works good.

    Leave a comment:


  • Cdub
    replied
    Those prints look good. With an FDM printer, there is going to be handwork to make the prints into something nice at the end no matter how much you fiddle with the printer.


    A few tips I could give you, for the car bodies (not the van) try printing with the model pointed straight up. So the front bumper would be pointed towards the ceiling. The details on the rear face and the front face may suffer a bit, but the rest of the car will look like a million bucks. I've experimented a little with breaking the body model up into parts so I can print them in different orientations. If you can just cut off the front 6 mm off of the body and the rear 6mm and print them in "normal" orientation, then print the rest of the body in a vertical orientation, that would be optimal.


    The VW van wouldn't be as good to do this with, because of how large and flat the front and rear end are. That overall geometry lends itself to printing as you have done here.


    I print the bodies for the car I've been working on on their sides. The body has a very flat side, so it sticks to the printer bed well. I end up with 10x the weight of the body as support inside the body, but the final part is pretty good.

    Leave a comment:


  • MrFlippant
    replied
    Great start!

    Leave a comment:


  • jivkoBG
    replied
    Hello again! Several photos from me.




    These are my first attempts. I still have printing problems, but I hope to get better results soon.

    Leave a comment:


  • jivkoBG
    replied
    Hello. I'm new to 3D printing. Soon I'm trying. For now successful only for rims. Now I'm trying to make a body. The rims are all my projects.

    Leave a comment:


  • MrFlippant
    replied
    Ah, that certainly could be. One would think the screw still had good contact with the braid, though. Soldering the braid to the wire, or just using the raw wire is a solution, of course, but being able to change braid without soldering or replacing wire is a good thing, if possible.

    Leave a comment:


  • Cdub
    replied
    The braid I'm using claims to be "without flux core", according to McMaster-Carr. However, I did nothing to treat it or verify that there wasn't something on the braid.


    I believe the issue was with my retention method. I was using a screw to "pinch" each braid into the guide flag. I believe I over tightened these and tore through the braid (at least one of the two). The damage was concealed in the flag, so it wasn't obvious what had happened.

    Leave a comment:


  • MrFlippant
    replied
    Desoldering braid has dry flux on it. Did you do anything to remove that, such as soaking in acetone? If not, then that's why you had problems with it. Either clean it, or use clean braid meant for slot cars.

    Great work, though. I look forward to printing up a car or two.

    Leave a comment:


  • Cdub
    replied
    Progress!

    After much more experimenting and troubleshooting, I have made a few more changes and finally have a car that runs!

    A few notes on motors:
    I built a second car and used a different motor. The link is below.

    https://www.aliexpress.com/item/AIYI...1f204c4dJaZ3ym

    I cut some of the shaft off from the end I wasn't using, and pressed the provided gear off and replaced it with a my own (different pitch).

    This motor works great with my track at about 12 volts. The power delivery is nice and smooth, and the car runs really well. So, the 13,100 rpm runout speed at 12Volts is a very good match for my plastic track and nomag car. I'm using Carrera Go! track, but all turns are either R2 or R3.

    The motor in my first car was a solarbotics RM1A. This motor is rated at 7400 rpm @ 4.7V. Running the track at 11 or 12 Volts makes this car extremely hard to control. Turning the track down to around 8 or 9 Volts is about right.

    A note on braids/brushes/pickups:
    The first car I built used desoldering braid for the pickups. It was soldered to the ends of the motor wires and appeared to be pretty robust. I don't know exactly what had gone wrong, but I was getting intermittent power through my braids to the motor. This, along with the too high voltage was making the car a bear to drive. I cut them off and switched to just using the motor wires splayed out for pickups and suddenly the car ran much better.


    I believe I have the chassis, pickup, and tires sorted now, however, I think the body is still hitting the track in some conditions. I have a little more refining to do in that regard. Overall though, I am much closer to having a formula ( and files) for a car that i'd be comfortable sharing.


    More soon.

    Leave a comment:


  • Cdub
    replied
    For anyone that is interested, I put together a write up about pouring lead weights in the scratch-building section:


    http://www.slotcarillustrated.com/po...86#post1048586

    Leave a comment:


  • Cdub
    replied
    Well, I got a chance to run the car, and it runs very well. The magnet is very close to the track, and so the traction is quite high. Indeed, it screams around the track glued down like the mag Carrera cars. My previous attempt at putting a magnet in the Dodge Monaco was flawed, as I just put a pocket into the chassis, and didn't really lower it closer to the track. Where it is on the car now, it doesn't seem to really do anything. Now I know.

    The magnet more in the middle of the car behaves interestingly, as the car will "step out" if you overcook it, but not just totally fly off. So, you have a chance to pull it back in.

    The gear mesh is a little rough. I'm hoping it will wear in if I can get out and run it more.

    The plastic I'm using is PLA, which is notorious for having difficulty bonding with glues. My 2mm guide pin is glued into the printed flag on a very small area and this joint just isn't very strong. I'm going to rework some of that geometry to make it stronger. Other than that, I'm quite happy with how this is coming along. I want to pour the lead weights and run that car as a no mag a bit more to see if I can figure anything else out there.

    I'm in the process of putting a more flowing layout in place to make evaluating a no mag car a little easier.

    I hope to have files I'm confident enough in to share soon.
    Last edited by Cdub; 07-12-2018, 05:52 PM.

    Leave a comment:


  • Cdub
    replied
    Pouring lead into silicone molds is a common technique across a variety of hobbies.

    I started doing it a few years ago for Pinewood derby. I've had success with OOMOO and MoldStar (both from SmoothON).

    The lead melter I use is similar to this one:
    https://www.jannsnetcraft.com/lead-m...774018064.aspx

    But the one I use is likely older than I am.

    Yes, you should wear welding gloves, wear eye protection, jeans, and closed toe shoes when doing this. Definitely go into the pour with plan for what you are going to do with the melter before, during, and after the pour, and take care to not have any moisture in your molds. Molten lead makes steam very quickly.

    As far as the interaction with silicone goes, it's not a problem. You can get dozens of good pours from a silicone mold before it begins to breakdown. On paper, the temperature capability of the silicone and the melted lead seem close, but in reality several things go your way. The lead begins cooling the instant it leaves the pot. The silicone starts at room temp, and every bit of energy the lead puts into the mold to warm it up takes temperature out of the lead. Usually, the largest surface area of the part is the open top where you are pouring, so all that heat just goes into the air. So, from a practical standpoint, it just isn't a problem.

    The most annoying part is the lead shrinks considerably as it cools. There is an art to "overpouring" your part with a little dome to it so when it cools it is relatively level. The great thing is that if you mess up, just throw the part in the melter and try again.

    If you just want to prototype something, and only need a few pours, you can make a mold from a pine 2x4. Just drill the hole or holes and do whatever you need to make the cavity you want and then pour away. The drier the wood the better, as you'll get less steam. The lead will char the wood which ends up protecting it. My point is that wood should "burn" around 500F, and I've never managed to set a kiln dried 2x4 on fire with lead.

    There are many youtube videos out there about pouring lead weights for fishing. You can watch them and judge for yourself the level of danger involved (and get a chuckle out of the decision making of some of the folks making the videos).

    Hope this helps.
    Last edited by Cdub; 07-12-2018, 05:51 PM.

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