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Front AT Bumper tutorial with video and pdf instructions

Discussion in 'Chassis Builds/Pics/Videos' started by ltr74, Apr 3, 2019.

  1. ltr74

    ltr74 FRP Popsicle

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    IMG_2750.jpg

    For a couple weeks I have been searching Instagram and Youtube to learn how to make the front AT bumper that we have been seeing from Japanese racers this past spring. I made one that works really well and documented the second one I built. There should also be an attachment with written instructions and diagrams at the bottom of this post.


     

    Attached Files:

  2. David S.

    David S. Spacer

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    Really comprehensive video and instructions: thank you for taking the time to put them together.

    Two quick questions:

    1) How do you trim your carbon/frp and get such a straight, smooth finish (particularly the back of that H bar). Do you do it with a Dremel and sandpaper or do you use a milling machine (or some other method)? And do you use the same method to shorten the brass spacers?

    2) Would I be right in saying that the sliding damper wouldn't clear your front wheels under the current set-up if you didn't have them reversed on the front axle? Is it possible to modify this set-up so that it clears conventionally-mounted wheels?

    Thanks again for the superb tutorial.
     
  3. ltr74

    ltr74 FRP Popsicle

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    Thanks,

    1. I trimmed everything with a Dremel with a cutoff wheel. The cuts on this are straight and easy so it's pretty simple. Curves I'm much worse at. I just lucked out that everything is lined up so well. My concern was more for clearance and the three screw holes just looked like a good spot to make a straight cut.

    2. I just checked and it is closer, but does not hit, but a few things about this, The tires I am running are 26mm, a newer trend is 24mm tires for open class with faster motor/gearing. I'm making new 24mm tires this weekend for this car. The FMAR I used for the end of the video already has 24mm tires and no problems. Also, my wheels are reversed to increase cornering speed. With normal wheels, it will likely hit even when the sliding damper is not compressed. I'm not too worried because I'm always running reversed wheels.

    Two solutions for running conventional wheels. Run 13mm rollers. The 13mm mount is further out and the smaller size should fit better. Second option is to trim only one hole on the FRP brake plate so that the whole plate is a little longer and give more space. You will need to shorten your rear brake to make this work, but it is an option.
     
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  4. David S.

    David S. Spacer

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    Was revisiting this excellent video and PDF (thanks again for the great detail), as I'd like to have a go building this bumper set up. However, I don't have spares of the 12-13mm double roller brass spacers. In the video you mention: "...if you don't have any extras you can buy them separately..." Is there a specific Tamiya part number for these? I haven't been able to find them in my initial searches so far :(
     
  5. David S.

    David S. Spacer

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  6. ltr74

    ltr74 FRP Popsicle

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    Yes, that is the part. You can actually cut the spring a little and not use the extra 3mm piece of brass tube. Cutting the spring means there is a little more space for it to compress when the AT system is used. That is what my current build and many others are using now.

    Also, we have switched over to the black springs instead of silver. It makes the system a bit softer and easier to activate.
     
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