Not been getting much done of lat due to pressures at work, (stupid reality getting in the way of my fun!
) but I have found some time this weekend to sit down and get some work done on the jet boat design, this time building on the success of the 6S 1900Kv inrunner 2:1 gearbox, I am making the following mods:
- New gears, this time hardened steel, MOD 1, 13T & 30T
- New gear ratio of 1:2.3
- New larger motor, GOOLRC 4074 2000Kv
- New 3D printed motor mount, gearbox plates (due to change in gear PCD & motor mounting holes)
Good reasons for these changes, new motor, bigger, better and who doesn't like more power?!?!
On a more serious note, jetdrive's are phenomenally power hungry devices, the 1900Kv works well, but even with water cooling, it is still very hot at the end of each run, so the thinking is this, bigger motor equals more torque due to increased mechanical advantage, this means more power and more power, leading to a less stressed motor, which means cooler running... well that's the theory.
With the new GOOLRC motor having a rating of 2000Kv, I decided to change the gear ratio, as I was changing the gears anyway, dropping the overall RPM will drop the current draw, which means cooler running and longer run times, I have also noticed from the GoPro POV footage that the jet unit sounds very laboured above 85% throttle, I believe this is due to a lack of flow through the unit, due to restrictions in the design, water in / out is not equal to demand, the new design of drive should address these issues.
At the moment, with the 1900Kv 6S setup we are getting a drive input speed of: 1900 x 22.4 = 42560 x 0.5 = 21280RPM, now this appears to be a tad fast, as I have found that this unit prefers speeds in the 18 - 19K RPM range, anything more than that suffers badly from the rules of diminishing returns, the new setup will give: 2000 x 22.4 = 44800 x 0.43 = 19264RPM, the parts for the new gearbox are printing as I type, so hopefully I can bolt it together tonight and get down the lake for testing tomorrow.
I also have news of the twin jet unit and some early work in progress screen grabs to share with you guys, as over the festive period I managed to start designing the new and improved unit, bigger, better and more free flowing than the old one, this will be a true 40mm unit, with the impeller OD being 40mm and the tunnel being 42mm ID, I have also redesigned the stator housing, opening it up to drastically improve through flow, the trade off is a slight decrease in flow velocity, but the increase in flow volume should compensate for this.
After a thorough inspection of the large fibreglass hull I bought, I have decided it will be less work in the ShedShop to 3D print an entire hull, instead of trying to make the new hull work with what I have, this works for me as I have very little time to physically get out to the ShedShop and do stuff, but my 3D printers can get a huge amount done when I am at work.
The new jet design will also come with a range of new and improved reversing nozzles, I have taken the excellent work that Yogibar has done and reworked his drawing to make it work with the larger unit I am designing.
With any luck more updates tomorrow after a morning of tearing it up at the lake!