More Power & E-Vent Version 3.1 Release

  • We conducted testing with a lung phantom, set to replicate low compliance lungs (typical with ARDS) and airway resistance. As a result, we increased our motor Power Calculation to 70 W. This has increased the motor torque, in our design, to 15 N-m, see Mechanical.
  • We are working to identify whether reasonably sized motors are available to meet this specification.
  • Reduced specifications of I:E = 1:3 and max respiratory rates of 30 breaths / min can be used, as per the AAMI’s updated Emergency Use Ventilator (EUV) Design Guidance, accessible from here (see reports section).
  • Photos of our latest reference design Version 3 have been posted to the Mechanical page along with CAD in Downloads. Details on earlier iterations have been moved to Past Designs.
  • We are tracking other groups and are starting to list them on the Resources page.

14 Replies to “More Power & E-Vent Version 3.1 Release”

  1. Henry Lopez
    Henry Lopez

    Hey there! Thank you again for your efforts. Talking about motors: you mentioned that you analized stepper motors (dont know if you analized the the NEMA models), and that you do not recommend the use of those, but I havent found the reason for that recommendation. Could you please elaborate on that?

  2. GK USAP
    GK USAP

    Our team is pursuing a dual stepper linear actuator design -one on either side of the BVM squeezing it directly. NH is correct that steppers are harder to control, but I suspect part of it is that those issues get compounded when a single stepper is driving a geared assembly. What we are hoping to achieve with a direct drive is the use of back EMF monitoring to detect motor stalls – this would insure full tidal volume delivery and work as a home switch.

    The advantages of this design are:
    – Very rapid assembly with no precision fabrication required.
    – Limited mechanical wear over time (ver very few moving parts, and the ones that exist are already heavily engineered)
    – Wide availability of supply chain for NEMA linear actuators (4 already well qualified suppliers, parts availability in 100k+ volumes/month).
    – More effective torque and speed can be delivered to the bag, allowing for higher I:E, RR, TV splits.
    – If we can get Back EMF detection working, no need for homing switches or position sensors.

    Downside;
    – Bulky, offset with some industrial design magic a bit.
    – Power hungry at the highest settings.
    – Can we get Back EMF detection to work reliably enough? We have 2 stepper manufacturers working on that right now.
    – Will require somewhat expensive stepper drivers (~$5 per motor)

      • GK USAP
        GK USAP

        We will be showing off our design when we feel like it is a viable path forward worth other teams exploring, probably in the next week or so. One challenge in developing these is that these motors are all sort of “build to order” given their wide range of available configurations, and the configurations most suppliers keep on the shelf for prototyping are never a 100% match to this project’s needs. Having said that, once we commit to production, they can be built in very large volume.

        We think the big problem with any design is the supply chain side of the equation. Our plan is to open source an AAMI 503:2020 compliant design using the dual linear actuator mechanism, and have distributed teams of shops anywhere in the world apply and get qualified to build them to a high standard. We’ll be building FDA EUA certified units here in Portland for bulk sales, and we’ll leverage those orders to keep the supply chain humming along for the local distributed teams who will be able to order knock-down assembly kits (motors, PCBs, power supplies, pressure sensors, etc) from us at cost. We think this is an effective way to overcome the supply chain issues, as we can likely place unit orders in the 20k-50k volumes that really accelerate suppliers to start flowing parts quickly. You can’t get that kind of supply if you are 10 or even 50 teams across the world trying to make these things in quantities of 100 or so.

    • GK USAP
      GK USAP

      Check the AAMI documentation. They just released that AAMI 503:2020 Rev 1 document I mentioned earlier, which is likely the path the FDA would go with. This document formalizes everything the MIT team has been working on, and would be the precursor to the FDA EUA process. With Ford/GM/Tesla all booting up processes to build licensed FDA certified vents, the debate is likely if this is even necessary for the FDA to green light.

      Of course, that is a bit silly as none of those large scale projects are shipping yet – they might have manufacturing challenges, supply chain issues, or (most likely) distribution issues where 4000 vents sit in a FEMA warehouse in Kentucky while New Orleans is triaging vents. Even more silly when the real key to an FDA EUA is to put *some* level of quality/efficacy/safety insurance on units to ship to the rest of the world. The US and Europe are soaking up 100% of all ventilator capacity and this thing hasn’t even really hit the southern hemisphere yet. Those folks were always short on vents, and they need something like this now more than ever. EUA approvals would cost the FDA almost nothing in resources, but would be a path to quality ventilators at a low cost for billions.

  3. Don Willett
    Don Willett

    Have you tried a stepper motor? I am currently designing a ventilator based on Arduino Mega with two pressure regulators(BMP280) plus Electrical signal pickups for diaphragm and lung expansion. I’m using a stepper motor and seems to have sufficient torque to do the job. It’s my first time doing this so I’ll keep you posted.
    Also using a tablet for all reference data and adjustments TX/RX from arduino.

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