Site Loader
Christchurch, New Zealand

The Razor 620 jetsprint design is feeling like it is 90% there. At the moment most features are stable and won’t be changed much. If all goes well its going to be small adjustments and tuning from here on out.

Here is what the design looks like at the moment. Hopefully everything performs as it should. I’ve easily spent 500 hours in CAD (without exaggerating) to get my skills from this:

Version 0.1

To this:

Kwikjet side by side comparison with Razor 620
New hull shape is a lot longer and narrower, and has a lot more strakes

I decided to keep the transom (rear hull profile) the same width so that way its no wider on a print bed. This way if you could print the kwikjet, you can print the Razor620. It turned out to be a little longer due to jetsprints just being a bit longer and sleeker. I designed all of this keeping in mind that I would want to reuse the same radio gear, motors and batteries from the kwikjet. The gear isn’t the cheapest and hey, its a pretty badass looking upgrade that only takes print time and a KG of filament. Not bad!

Cross section – good view of the 2 stage pump

I decided to try a 2 stage pump. At first I didn’t intend to fully commit to a 2 stage pump but eventually I did. The kwikjet used a 35mm jetpump with 23.5mm nozzle. 28mm pitch. This one uses a 30mm pump. Simply because I wanted to keep it as scale as possible. The real jetsprint boat I’m going off is 3.9m in length. This one being 620mm long puts it at 1:6.3 scale. A Hamilton 772 jetpump is a popular choice for racing jetsprints. They use a 7.5 inch impeller. At 1:6.3 scale that puts me right on 30.15mm jetpump – hence my choice to go with a 30mm pump unit.

The nozzle diameter was chosen in a similar fashion, settling on 16.3mm. I chose to use 28mm pitch with this pump as it seemed like a good starting point. I have a power meter that I’m borrowing from a friend that can handle up to 100Amps that I will use to monitor amps when it comes time to test the pump, if the current draw is too high/too low I will adjust the impeller pitch accordingly or play with motor/battery configurations. At my disposal are 3S and 4S batteries, 1900kv and 2250kv motors. this allows me to try a whole range of speeds and find a optimum.

This top down view of this airborne boat proved very useful LOL – hope the drivers came out ok

So, its looking great. But will it perform? Only one way to find out. I’ve left a lot of the development thought process out here since I’ve already finished that part. It was a long and tedious process with many edits, oohing and aahing and pondering on certain design decisions, see what will fit etc.. So I’ll just put some of the briefs here so y’all have a bit of the background 🙂

Onward and forward! Its 3D printing time! Takes patience… this project takes about 1KG of filament and just over 3 days to 3D print (hey, thats if you can get them printing back to back. So its more like a week given time to switch over the print jobs unless you like getting up at 3am to switch prints since that’s not happening haha)

Leave your comments/questions below!

Post Author: Jotham

Leave a Reply

Your email address will not be published. Required fields are marked *