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Advice for Engineering Test Bed Build

Old 04-05-2020, 06:08 PM
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Jsmeberg
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Default Advice for Engineering Test Bed Build

Hi all,

I'm looking for advice on a new build. I want to put together a large 36-48" (maybe bigger) mono-hull, planing hull, no frills test bed. The goal is to do small scale (lower cost) development of drive systems and propellers for the real thing. The alternative to an RC build is modifying a real boat so price isn't so much of an issue. Basically I want the beefiest electric power system i can get with off the shelf parts. I need something that can do moderately high speed and also generate a great deal of torque for complicated drive trains and large props. target for max prop shaft speed is 7000 RPM. My current power system plan is as follows:
Motor - Turnigy AquaStar T20 Brushless in the 1280kv mode.
ESC - Turnigy AquaStar 200A Watercooled Sensorless.
Battery - ZIPPY Compact 4500mAh 10S 35C Lipo Pack w/ XT90.
This all would be run through a gear reduction to give me around 7000 RPM at full power I'm new to toys of this power so a couple of questions. Will these parts to work together reliably? Is there a better component or set of components to achieve my objective. How many of these battery packs should run I for a decent operational time? Finally am I crazy and going to blow my boat up with this kit? Any suggestions comments etc. are greatly appreciated.

Thanks all!

Last edited by Jsmeberg; 04-05-2020 at 06:09 PM. Reason: Grammar
Old 04-18-2020, 05:10 PM
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Chrisg81983
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You are going to need one heck of a prop with only 7,000 rpm.... what props are you thinking of ???
Old 04-18-2020, 05:56 PM
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Jsmeberg
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Thinking something 3-4 in Dia, five or six blade with a surface piercing profile on the blades. I'm pretty sure nobody makes something like that so it will be custom work. I am going to start out with 3d printing which will probably not be able to handle the loads so then maybe onto aluminum castings or finding someone with a 5 axis mill. I know the size and RPM range is pretty unconventional for an RC boat but I'm not trying go fast, I want to do low cost research. Don't know if it will work or not but that's the business: prototype, fail fast, and iterate or move on.
Old 04-18-2020, 06:45 PM
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Chrisg81983
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Wow would really love to see this, but I would definitely use a big outrunner or big lehner. I would also use a mgm 400/63 controller. I mainly run mgm with lehner and can pull some crazy numbers with that combo.
Old 04-28-2020, 02:14 PM
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asupervee72
 
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I was recently looking at the power combo you listed for a large scale jet boat project I was cooking up but they are backordered. Have you considered looking at any of the electric skateboard set ups? The are low kv so you would not need a gear box . Something like a 190 kv on 10s should put where you want to be. Might even be cheaper. You would need to take added precautions for waterproofing though, a conformal coating usually does the trick.

Your prop diameter to boat size ratio seems off. Are you doing this in a water channel? Open water? Is this a static test you are setting up. Can you say more about the goal of the test bed. What kind of data are you trying to collect?

For batteries I wouldn't do a 10 s pack but 2 matched 5s. This will make charging easier as most chargers have a 6s limit and even higher end chargers only bump it to 8s. I've had good luck with the zippy compact packs, it would be between those and the turnigy hd packs. I have the 60 c version of both, I would stick to higher c rated packs, they sag less and typically have a higher charge rate as well.

Last edited by asupervee72; 04-28-2020 at 02:21 PM. Reason: additional comments
Old 05-02-2020, 08:09 AM
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Jsmeberg
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Thanks for everyone's input and interest.
I'm planning on doing open water testing on a small, normally very calm, lake I have access to.
In relation to prop to boat size ratio i how have the plans in CAD for a 54 inch hull and likely wont go over 3 inch diameter on the props.
For data Id like to collect: Motor amperage draw, Voltage across the motor, Motor RPM, shaft RPM (past gearbox) to characterize the power output. I want to use a GPS module to record position velocity and acceleration to characterize performance with different drive/prop configurations. Finally Id like to have temp and battery voltage red outs to monitor the health of the boat. Oh and a gopro mounted on the transom looking at the props

Since I last posted done a lot of research and looked into a wider range of product offerings. This is the power system up I'm moving forward with, as parts are in the mail or have already arrived.
Motor: SSS-56123 at 500kv, the longest can hobby brushless I could find. She'll put out damn near 10kW pulling 188 amps from a 12s source. The 188 amps keeps me from moving to a more expensive esc like a ZTW seal. There are motors that put out more power in a similar price range but there are a couple of factors that I think makes this one perfect for my application. The motor tops out at 25k rpm, this makes building a gearbox that wont explode much easier than it would be with some of the higher rpm brushless offerings. In addition the long case size, 10mm output shaft, and lower than average rpm tells me the motor is built more for torque than high speed power output. Granted this is still a brushless and ill be running a 3:1 reduction to get the most torque out of it.

Battery Pack: 5800 mAh 6s 25C zippy compacts. Four of them. Two series linked pairs connected in parallel. Each series pair makes a 5800 mAh battery pack that will give 12S voltage at a nominal potential of 44.4 volts. 25C rating means I can safely pull 145A from the pair. Then two of these units are linked in parallel giving me 11,600 mAh for max useful run time and way more amperage draw than I will ever need. This system was planned and purchased when looking at higher amperage motors so is kinda overkill for my choice of motor, but it shouldn't be a problem.

ESC: turnigy aquastar 200A. This is definitely the weak link in my chain but I was getting kind of intimidated with the 300 dollar ESCs. By its specs the turnigy should be able to handle what I'm doing here without letting the smoke out but I'm not super confident in it. If anyone has experience with this particular ESC let me know your findings.

I still need to solidify plans for a cooling system, transmitter and servo set up, and data collection/telemetry system not to mention hull, drive, and props. Silver lining of the current lock down is I have lots more free time now that I'm working from home.







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