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  • HObro
    started a topic Minnesota Twins

    Minnesota Twins


  • HObro
    replied
    Per Ed's suggestion...reversing the positioning of the two crown gears, having them inboard of the pinions instead of outboard. And trying a couple of different motors.

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  • HObro
    replied
    Thank you!

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  • model murdering
    replied
    When the motor is energized the armature becomes another electro magnet between the two already existing permanent magnets. When you have the juice on, the total magnetic field intensifies. The more juice, the stronger the elctro magnet becomes, and thus more attraction. With the juice off, the fields arent combined. In the case of your Twinns, the effect is doubled.

    The higher you rev, the grabbier it gets.

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  • HObro
    replied
    Could you dumb this down for us mere mortals?? ;-)

    there is an impressive amount of on throttle flux assist when cornering, due to the greater combined field being directly exposed to the rail via the drop through configuration.

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  • HO RacePro
    replied
    MM,

    Thank you much! And here is a 1/50th scale dollar for your troubles!

    Ed Bianchi

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  • model murdering
    replied
    EB: I'd like to read MM's opinion on how well controlled the rear axle is, given its unconventional inboard bushings.


    Of course Ed, you know Im always I'm happy to toss it around a bit. The center "bushing" in this case works as it should, with no peculiar behavior exhibited at this point in time. After a lifetime of being a fixer, some things just feel right to the touch; and at our venerable ages, we most certainly dont fix things that aint broke.

    My additional observations will continue to evolve; as I ponder all the fun I had playing with Jeff's build. Like any other axle the Twinns rear axle will take a "set" and locate itself within the provided tolerance, based on the force and direction with which it is applied.

    In the case of the Twinns, there was more clearance between the axle and the rear axle bushing than I personally would like to see, but I am often proved to be an idiot by what "will" run flawlessly in spite of my observations and preferences. What I found interesting was that the simultaneous, outboard, dual motive force kept the axle firmly planted across the center. I also consider that; for what the design gives up in support on the ends, the available surface area of the centered journal is easily four times what one normally runs in a typical two bushing conventional arrangement. My new take is open to the idea that any static axle "walk" initially exhibited, is "set" flat across the center journal when loaded on either end. Submission by force!.



    EB: Also, there is a brass post mounted at the rear of the chassis. I suspect its function is to keep the body from contacting the rear tires. True or not?

    I too assumed it was a standoff at first, but it's a bit short. Notably the chassis features the tried and true pin receptacles, 2 per side.


    EB: The dual motor drive might result in more powerful braking. Zat so?


    No sir! Once the platform was track sorted, the Twinns would pipe down the track on throttle, and glide down smoothly off throttle. As mentioned earlier, the finger roll was silky smooth and feather light, like that of a Mega Gee Plus, if you are familiar with them. They are completely devoid of any cammed feeling like armature poles clunking through their rotation when Polys or Neos are present for a finger roll. Additionally, if a mini can isnt snatching tools and whatnot off the bench, they arent poly or neo mag. No need to open them to look. No mas, because there's no gauss.

    Braking is what you'd expect with an easy roller motor: Essentially "flywheel over friction" due to little or no magnetic lug at the de-energized armature poles. With two armatures and middling ceramic magnets, there is a bit more flywheel effect than I expected. Nothing a dynamic braking circuit wouldnt fix.

    Interestingly, with the two motors, there is an impressive amount of on throttle flux assist when cornering, likely due to the greater combined field being directly exposed to the rail via the drop through configuration. At 1.60", with RC minicans, at 18v: one should be able to punch the tail out at will, almost anywhere you want. Such was not the case. In fact the Twinns resisted my attempts at sideways mayhem with considerable attitude, until the tires were sufficiently fuzzed up. I noted the combined field effect when I had the chassis on the track, tail slightly up for wiping the tires. I squeezed the throttle up; and immediately felt rear assembly suck down like the old AMRAC chassis, that would pinch your finger, albeit not as aggressive..

    I could blather on a while about this and that, but FWIW, thats my two cents Ed, and a penny back in change
    Last edited by model murdering; 08-13-2019, 09:29 PM.

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  • HO RacePro
    replied
    HOBro,

    Thanks for the props on the soldering thread. I looked back at it just now and saw that all of my photos are missing -- broken links from the SCI port-over.

    I guess I'm going to have to restore those photos myself. And also to the other sticky threads I've created or contributed to. Something to do when I'm in the mood to do mind-numbing repetitive work. And yes, it does happen to me.

    Ed Bianchi

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  • HObro
    replied
    I am going to build another one (lessons learned and all that) trying some different motors...and YES... I will reverse the crowns to the outboard sides.

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  • HObro
    replied
    Hi Ed. The brass post was just something put in to firm up the axle when I installed it. And that reminds me... I need to read through your soldering tutorial a ba-gillion more times. Thanks for that!

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  • HO RacePro
    replied
    I'd like to read MM's opinion on how well controlled the rear axle is, given its unconventional inboard bushings.

    Also, there is a brass post mounted at the rear of the chassis. I suspect its function is to keep the body from contacting the rear tires. True or not?

    The dual motor drive might result in more powerful braking. Zat so?

    Ed Bianchi

    Leave a comment:


  • HObro
    replied
    Bill, cannot begin to thank you enough for taking a look at the Twins! I had been happy using the conventional shoe module (a sawed off BRST G chassis secured to a brass pan), and on this iteration... I went a bit overboard on ensuring that the module was bullet-proof enough to stay secured to the brass...hence the brass posts that ultimately caused the front wheel snagging. Regarding that, back to the old drawing board. I am going to try using this method again, but perhaps constructing my own shoe module...maybe with Plastruct. One thing that was mentioned by another poster...was the appearance that the front tires were not actually touching the track...from what it appeared to me... the spring tension was just too strong for the weight of the front end (I used .007 springs) does anyone know if there is a .006 made? Otherwise, I could try removing a coil or two. Thoughts?

    Bill, thanks again!! Mucho appreciated!

    -Jeff

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  • model murdering
    replied

    Minnesota Twinn 1: Sleeping Beauty

    H0Bro's pix dont do this build justice. At a glance, it appears to be a beast; but actually, she's very refined. I proceeded with some reverence for it's originality, and tried to make the platform work as delivered.

    On the finger roll, the dually set up meshes smooth as silk, but the first voyage was a sputtering no go. The motors ramped up nicely on the gator clips, with no weird oscillation or vibration in the rear components, and I'm glad. That rear section is a tricky little bit of fun, so it was good news to have the tail be skookum.

    Nice motor ramping when energized from the shoes is good indication that the shoe geometry requires some adjustment, as was shown by the lack of lineal burn we saw on the contact patches in the original pic. Per earlier observation, the contact patches needed heeled down, with an equal amount of toe toe-up rolled into the shoes. As mentioned previously, the intention is to have the shoes parallel to the rail, with the chassis's front shoe hanger centered in the shoe's hanger window. This subtle angular adjustment is frequently over looked, when folks raise or lower their sprung hard-shoe cars.

    The second voyage resulted in some consistent motation, but was a jerky clatter fest. It was obvious that we werent up on plane yet. Re-inspection revealed three different, but related issues, that were scrubbing speed/performance. The Twinns sit on a flexi design chassis using a traditional, longitudinal piano wire, amidships. The "twang" is held in check laterally by slip pins in the port and starboard frame rails, at the rear bulkhead. I studied on the aftermath for a bit.

    1. The motors were dropping through the pan and dragging the rail with the chassis at rest. Evidenced by the racket, and obvious scuffing on the cans. The drag is exacerbated by the motor's magnetic attraction to the rail. Merely a lack of pre-load on the piano wire, allowing the motors belly down too far. A slot car hernia of sorts. Easily remedied by a calculated bend, so that the motors had clearance over the rail, at the maximum downward hinge of the chassis. This subtle adjustment made the chassis functional.

    2. At first glance the shoe module always had a bit much back angle. Even though I wrestled the shoes around, the burn was still off. We were still plowing, evidenced just by the sound. Skkkkkkkkkuh .... is not a happy shoe. Closer inspection revealed that the shoe module was epoxied in, but had slipped the clamp at some point, and sagged down at the rear. I just broke it open, surgically removed the excess epoxy; and re-epoxied the shoe module into a more level position, relative to the chassis line. This brought the contact patches into a location where one can fine tune the shoes fractionally, for any rail or profile height differentials.

    The re-test was sweet silence, other than the metal guide pin banging around the slot as the chassis side loaded in the turns. This chassis is noticeably clean and flat through the turns. With a build triangle height of 1.60", one would expect a little more "on throttle" push coming off the apex, but typical of drop through arrangements exerting some anti-gravity effect, this chassis holds the exit until the bitter end, then comes right with a quick shake of the tail. (Think "drop through" Riggen.) I did not open the cans, but based on the lack of ferrous objects "porcupined" to the motors after being on my bench, and the easy finger roll, it's safe to assume the motor magnets are ceramic ... but one has to remember to double the width of the magnetic effect, because its a dual motor.

    3. There was still some abnormal wiggle and burn when coming back on the throttle, considering the silly foams fitted were virtually new; indicating she was still plowing, if ever so slightly. The cause? Random front hub drag. Fairly common. It will generally give you a twitch where the exit transitions into a straight. On the bench things turn freely when you flick them with your finger, but add a little side load and things start grinding or bucking. The independent front wheels are 'loominum of course, in contact against a brass alloy frame rail. Not my favorite materials to be side loading in the first place. The axle carriers were filed back a skoshe on the vertical line. Then some Wizzard nylo spacers were squeezed in to eliminate the hub scuffing up front. The frame spacing is right at the ragged edge, so you have to center and set the axle between the spacers yourself. H0bro can take a little off the back of the hubs, if he wishes.

    All work was minimal and non invasive. Although H0bro covered the bases and sent extra motors, I made the choice not to violate her. Personally, I wouldnt change one dang thing about this build. It's a wonderful project, that should have a clear or tilt nose lexan mounted on it; in order to show off it's unique and intricately delicate construction. She's not a blistering missile, but plenty fast enough to light them up, slide the turns, and now able get out of her own way at 18v.

    *********

    The instructive bit is, that other than a few degrees up on the hinge wire, and few degrees back on the shoe carrier; this build was essentially RTR.



    Last edited by model murdering; 08-12-2019, 08:23 PM.

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  • HObro
    replied
    If you don't mind luke warm, I will send you one!

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  • RichD
    replied
    I just thought of one advantage to having two motors wired in series. As I mentioned earlier when you only have one motor you usually need a resistor or diodes wired in series, even when you are running at 12 volts. I find that I need to choke back to about 9 volts. If you were running the track at 18 volts and had two motors wired in series each motor would see 9 volts.
    I see that someone owes me a bottle of water, but I am not gloating or anything.

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