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Positional Sensing Woes

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  • #16
    Originally posted by Pulsc View Post
    I really enjoy reading the theory about these kinds of things, thanks for that. The only question I have is in regards to this section. Roland triggers, and many others, don't follow this rule and yet they get perfectly usable results with the positional sensing. All the Roland cones I've seen cover the surface area of the entire piezo. Is there an explanation as to why it works fine for those builds versus your suggestion here? Thanks.
    AFAIK the piezos need to flex to work and Roland cones have not the entire base glued, only the inner part wide as piezo's ceramic is. Also on piezo the ceramic part is thick enough to not let any surface over it to touch also the brass surface.
    Roland TD-12 module, MegaDrum Trigger module, DIY DareStone CLDRUMWH A2E drum conversion, DIY rack using Dixon clamps, Pearl P-932 double pedal, DIY A2E Chang dual zone cymbals.

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    • #17
      Originally posted by Pulsc View Post

      Roland triggers, and many others, don't follow this rule and yet they get perfectly usable results with the positional sensing. All the Roland cones I've seen cover the surface area of the entire piezo.
      This is my biggest question about this design.

      AFAIK the piezos need to flex to work and Roland cones have not the entire base glued, only the inner part wide as piezo's ceramic is. Also on piezo the ceramic part is thick enough to not let any surface over it to touch also the brass surface.
      And thanks for the response redtide!

      Here is the drawing I came up with for my piezo base. Is this something like you are describing? I would place the piezo on the top foam doughnut to allow the ceramic to flex freely.

      piezo platform.jpg
      Last edited by Aka Wayne; 03-12-19, 04:20 PM. Reason: More details.

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      • #18
        Originally posted by Aka Wayne View Post
        Here is the drawing I came up with for my piezo base. Is this something like you are describing?
        No, I was talking about the surface over the piezo's ceramic where the cone has to be fit, not the bottom part, usually I put some adhesive in the center of the brass below the piezo directly on the surface I need to put it on where the glue made some thin thickness to let the remaining part to be free, otherwise I've read someone to imitate how Yamaha does it with a half circle of some rubber in between.
        Roland TD-12 module, MegaDrum Trigger module, DIY DareStone CLDRUMWH A2E drum conversion, DIY rack using Dixon clamps, Pearl P-932 double pedal, DIY A2E Chang dual zone cymbals.

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        • #19
          Thanks my drawing was more in reference to Sascha's post. What sort of platform do you secure the piezo to?

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          • #20
            This is my first attempt to make an aluminum crossbar trigger, more or less like the ones I use now, except here some rubber grommets are missing on the iron plate's holes for the bolts.
            I use 1mm biadhesive foam to fix the piezos on both aluminum and iron plate. I don't think it's much different from other triggers built by other users in this forum.
            The cone was made using some soft EPDM layers, cutted with an electric knife.
            Roland TD-12 module, MegaDrum Trigger module, DIY DareStone CLDRUMWH A2E drum conversion, DIY rack using Dixon clamps, Pearl P-932 double pedal, DIY A2E Chang dual zone cymbals.

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            • #21
              Thanks so much for the picture. That looks a lot like my set-up though. It appears you have an adhesive foam disc right under the ceramic part with the brass part floating free. Sascha (and I thought you were) is suggesting the opposite. Allow the ceramic to float and secure the brass edges via adhesive foam cushioning. Redtide, are you getting consistent PS response from this setup?

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              • #22
                I didn't have other pads than the ones I did so I can't make a comparison, I can see that PS is working once the scan time is set and the small bar moves on the display from center to outer position in advanced settings.
                Roland TD-12 module, MegaDrum Trigger module, DIY DareStone CLDRUMWH A2E drum conversion, DIY rack using Dixon clamps, Pearl P-932 double pedal, DIY A2E Chang dual zone cymbals.

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                • #23
                  Thanks! Is you're ceramic part free to float via your glue bridge you described?

                  From the picture it looks like there is a cushion directly under the ceramic which would impede its ability to move. It also looks like the brass is not attached anywhere and free floating. That is exactly how my mom PD working triggering is set up.

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                  • #24
                    Originally posted by Aka Wayne View Post
                    Thanks my drawing was more in reference to Sascha's post.
                    The drawing is pretty much how I do it, except for the top rim which is solid in my case. I think having soft foam is counterproductive there, I wouldn't do it, and just have foam at the very bottom. You only need one decoupling layer, which is the bottom.
                    If the piezo is 'sandwiched' between two foam layers (where the cone is already one), the response curve becomes highly exponential. You can use that to tailor the dynamic response, but I personally would try linear first. Some additional flex layer (and thus exponential response) might be needed for large forces like a kick drum. In fact, my original MarkDrum reverse-beater pad had the piezo between two thick cellular foam layers (~1.5cm each), with the piezo residing on a large metal plate in between them. It didn't have to flex at all because of the large force from the beater, and upon dissecting it and measuring with a scope in long-term mode I could see the response curve change from linear to exp when the bottom layer is brought in. So, in order to capture light ghost notes on a snare, I would be cautious with the ground-plate foam height, or have a heavy plate installed over it that adds inertia.

                    On the brass vs. ceramic side: I'm facing the ceramic to the top. My solder joints are very thin (very thin wires), and I make careful & tiny cutouts on the foam for the wires and the ceramic's solder point, so that the rest can reside flat-on. I'm using double-sided TESA 456, aka 'killer red tape'.
                    I choose the ceramic side since that is where tiny hits get transferred best into voltage, not the brass. It might depend on the actual piezo, though, and it might also be better to have the cone on the brass for better or more even contact. But I'm cautious with wires residing on the underside & hanging loosing. 'In the middle of the action', they can easily add low-frequency partials to the waveform, but on the ceramic side, encapsulated by the cone (or cylinder, in my case), they're tight and can't add up anything.

                    Last edited by sascha; 03-13-19, 03:20 AM.
                    MarkDrum YES e-kit highly modified (DIY hall-sensor based hihat, low-volume trigger cymbals, 16" DIY kick, 12" DIY snare + tom 3), Triggera 10" splash
                    Gibraltar 9607NL-DP Legless Hi Hat, Intruder Double Pedal
                    Shure SE215 in-ears w. CustomArt silicone tips

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                    • #25
                      Your information has been great Sascha! And thanks to everyone who has chimed in in this thread. This is such a great and supportive community.

                      I'm going to try a 1/16 epdm bottom layer followed by 3 1/16 washers and a 1/16 abs ring to mount the piezo to. I'll try a quarts come on top as those go right to but not over the edge of a 35mm piezo. It will probably be a while before I get the pieces and try it out. Will report back!!!

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