Very cool! I managed to do a pull test on the lake this weekend with a fish weight scale. Very cheap method to measure thrust by the way. I pulled just over 40lbs of thrust at full throttle again pulling about 95amps at 24v. 2,300ish watts or 50watts/lbf. MHZ’s 52mm jet advertises just about that (240kN) but the 65mm variety scale up to around 400kN so i have some more work to do. I’m about 66% rpm right now too so i need to couple a new motor setup to hit my total rated speed and thrust. So far none of the plastic has stressed but were about half of the thrust we are looking for.
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the fish weight scale sounds like an easy way of measuring.
I am going to have a look at this.
It works very well for the type of testing we do and gives a good baseline to go off of. One thing to make sure is, whatever tow line or method you secure to the scale, make sure it is on the center of thrust vector or your number get skewed slightly.
Edit
Also i’m finding its hard to find a reasonable fish scale beyond 50lbs (the thrust we’re flirting with), so we might need something different going forward. I might look into a straight up transducer.
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Maybe use a single pulley? This will 1/2 the pulling force!
When you say you used a 4084 motor, was that a single jet, or twin jets? the Jet 4 setup with that motor lookls to be good value for a twin setup (8kW total power), if that would provide sufficient push, i’m very tempted…
Yes if you use an MHZ jet4 a 4084 motor will work. I built a single drive using these components. It was not very fast but it was reliable and long lasting. 8 am a big guy and it was mounted on a paddleboard so the performance was ok considering the limitations. If you use 2 jet 4 pumps on a shorter board and you are not 225 lbs like me you can expect to get a top speed in the 12/13 mph range. I only used 6 s or 26.2 volts on this set up. The jet 4 has a maximum rpm of 18000 rpm versus 16000 rpm for most other jets so an 8 s setup may be a better choice…check max voltage on the motors before deciding what components to run with.
My caution was more specifically against using the 4084 motors with the youngste 53mmr jets. That’s the set up that failed on me over and over. I popped the 100 amp breakers on first test. Then I replaced them with 200 amp breakers they did not pop but I baked the windings of both motors in seconds. The jet 4 is a 49 mm impeller I believe but it produces a lot less thrust so demands a lot less power. The youngster jets are beasts pulling high amps and producing lots of power. Disaster for a big guy on a long heavy board as the impellers and stators have cracked and broken several times for me. It remains to be seen if they hold up for others but i don’t think as currently built with epoxy resin they will hold up to the kind of abuse a jet pump is put through every time it’s used. Gimme two of em with bigger shafts and alloy impellers and stators… and replaceable bearings and they are a winner until then I will stick to MHZ products
Sweet, thanks for sharing. I love the crazyness of some of the twin 53mm setups, but Im looking at bang for buck.
Your welcome. When I started building with the jet 4 I had no clue and bought a couple of good RC 200 amp 6 s esc’s for $35/$40 each and they actually held up fairly well considering the load they were under. If you are under 160 lbs and have a light board you can get away with lower voltage esc’s. The goo. RC are a toy speed controller but if you can find a couple of 8 s speed controllers rated for 160 amps you are probably fine. I know I rebuilt that jet 4 set up after I wore it out over 2 years and I had a seaking 160 amp 6s I think laying around so I stuck it onto that setup and it has run great since … I think I got it used for $90
Just another idea to save the $$
Cheers
Re. Melting epoxy.
I was the person who talked about the bearing races shifting due to heating the epoxy… to clarify I suspected that this happened due to continuing failure of ONE of two youngster jets. I think it may have happened when I spun up the motors and jets on the bench after install. However I can’t say for sure without taking the jet out and cutting it in half to look. I had hoped to get a new jet from mark so I could do just that and still have a working jet drive, but Mark has not been at all helpful since I brought this to his attention. I have seen 3D printed jets that appear to have sleeved internals so that sounds like the fix for this issue. As far as The plastic/epoxy holding up under load, my personal experience is that neither the impeller nor stator do well I have had 3 impellers fail and both nozzles show chips of plastic missing from both stators. These are marks 53 mm jets I can’t speak to any other plastic jets. And I fully understand that at 225 lbs on an old heavy SUP loaded with a big battery pack etc I am asking the jets to push 300 lbs or close to that so it may be less a flaw in marks design and more a weight limit. I am klan seems to be having good luck with his set up. Mark has stated to me several times that there is no weight limit. I have had nothing but issues with these jets versus flawless performance from MHZ jets. And I have also built two drives from the Chinese knockoffs of MHZ ( before I knew about MHZ and also has failures of impellers, stator, bearings and in one case a shaft snapping in two pieces. The Chinese suppliers do not sell any parts either I did ask so for me anyway The only product that has performed as stated and not failed in any way and have all parts available for every product has been MHZ. I sound like I work for them I know but out of 6 jet pumps I have bought the two from MHZ are the only ones still going on original parts.
Cheers Frankie
Could you please link for the Chinese mhz waterjets?
I don’t have a link I believe Horizon hobby sold them and hobby king carried them with a hefty markup.
They were about $50 less than a real MHZ jet52 and no parts or support available so if you want a jet52 buy an MHZ the Chinese version works perfectly until a part fails and every moving part failed for me. Impeller, stator, bearings and even the impeller shaft.
What do you think of these? https://www.aliexpress.com/item/4000643150931.html?
Thinking of running a dual jet drive system with these. They are 50mm. Using 56123 500kv 10-12s motors 400a esc, you think they would put up with the load around 200lbs?
Reason I like them is that they would be flush with my boards thickness of 3in so just about. Boards 8ft x 2ft at the beam.
Thanks
Was following your progress, what happened?
It seems to me to hit the thrust required by the jets you need to up your RPMs to 17k atleast and possibly a 12s setup with the 360kv motors, like 56123s to reduce the heat, and increase the loaded RPMs using that 65mm prop.
Would love to see some more data on your setup if you up the v’s.
Your link isn’t working, try uploading a picture maybe?
search for item 4000643150931 on aliexpress
Oh, I see, these are 3D printed and I just happened to know the seller, can’t recommend these for a heavy duty/harsh conditions such as jetboard.
You’re going to spend endless amount of time to get them right, the impellers on those are not balanced at all and will probably vibrate untill you break something, water will rush into your electronics etc etc… just my two cents.
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I see, thanks I apreciate the feedback. I was thinking to use 3 of them on one jetboard 40mm to 50mm each, any tips on where to buy good reliable ones?
If anything, you could buy one of his 85mm jets, those are good, coupled with 83100 watercooled motor and I guess you’re going to see some speed, can’t guarantee tho.
For other motor manufacturer lookup FreercHobby, they got big motors, affordable prices, you might want to invest in good quality parts upfront so you don’t end up upgrading for years.
I built a jetboard and sold parts, building it was fun however not an easy job, especially if you go for dual jets.
If you need more info you can dm me.
P.S. I saw @jakebarnhill1 built one helluva jetboard, unbelievably fast, maybe in the future he would share what’s under the hood.