There’s your problem!

The most recent version of the Decimus 4 chassis runs reasonably well and, with the test release of the Decimus 5 Software it is more clever (I hope) than ever. However, it still can’t corner as well as I had hoped.

There seem to be two problems. First, the motor mounts are 3D printed and not as stable as they need to be. Over time, one of them has taken on a slight curve. In the photo below, you can see that the wheel at the front, on the right of the photo is slightly out of line. That can’t help.

Decimus 4 tyre wear

Decimus 4 tyre wear

The other feature you should notice is the uneven tyre wear. After just one contest, plus practice, this is what new tyres look like. It looks like the tyre at the front on the left of the photo is not getting scrubbed at all. Since my mouse CG is biased to the front of the mouse, I would expect the front pair to show less wear than the rear pair but they should be even from side to side. It is hard to see how the mouse can turn accurately with out all four tyres firmly and evenly planted on the ground. The solution is probably to shim the mounts. In the next post, I should be able to demonstrate how you can get the tyre load even all round.

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10 Responses to There’s your problem!

  1. How hot do your motors run?

    Could this be a result of the motors warming the prints and allowing them to deform?

  2. Peter Harrison says:

    The motors never get hot. Perhaps I should try harder 🙂

    It is just the Shapeways material the mounts are made from. It is not as rigid as I need I think. The next ones will probably be ABS or acrylic and the fan mount will add stiffness.

  3. Green Ye says:

    that’s why we do rotation test during the maintenance for our cars, I meant the real car.
    detailed material in shapeways are too soft.
    Is strong and flexible plastic strong enough for thread taping?

  4. Peter Harrison says:

    I have only tried the “detailed” material. It does not take a thread very well.

  5. Green Ye says:

    why don’t you buy a CNC machine instead then? Even the mount made by CNC is not guaranteed to be perfect as long as you tap the thread by hand even with guide.

  6. Peter Harrison says:

    I no longer have a good source of income or I would. All donations gratefully received 🙂

  7. Green Ye says:

    well, I am not talking about those expensive ones.
    Check those 3020 CNC sell on Ebay for slight above $500 USD with parallel port(the only downside, however if can buy a PCI-E/PCI to parallel port adapter for about $10 if you have a desktop).

  8. Ken Hewitt says:

    I noticed this a couple of years ago when I built my first 4 wheel chassis, when the motors were not fitted and so the wheels were not coupled I saw that only 3 wheels were rotating when I pushed it along on a flat surface. I am now working on a design which will have a very small amount of suspension on each wheel.

  9. Peter Harrison says:

    I would be very interested to see that.

  10. Ken Hewitt says:

    Still early days, I want to be able to 3D print it all in one go.it will only have about 1mm of travel so should be easy to print.

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