Preliminary Propeller Efficiency Testing

propulsion

#1


Recently at OpenROV Headquarters, we did some tests on the efficiency of various propellers which we thought might be good alternatives the to E-Flight Delta-V 15 ducted fan props we have been using so far. The original selection of the Delta-V 15 was really made primarily because it fit (mechanically) very nicely with the motor we had selected, and it "looks about right", but the only hydrodynamic analysis we did was pretty crude. We decided to get a little bit more scientific...


For this first set of tests, we selected two propellers to compare to the Delta-V 15:

The Graupner 2310.60 and the Graupner 2308.65

The objective of these tests would be to measure the efficiency of the selected props by comparing the thrust they produced when spun by one of the brushless motors we use for OpenROV and comparing that to how much current was consumed in order to achieve that. To measure thrust, we used the open-source test stand that Colin Ho designed and built several months ago.


We plan to do more thorough testing soon (which will also have a much more thorough write-up), but in the mean time, we thought it would be good to show some initial results. Bottom line: the Graupner 2308.65 gave us a more then 200% increase in thrust/current efficiency!

This means that among other things, simply by changing props, we'll enjoy:

  • Much longer battery life
  • Less thermal issues from the ESCs
  • Thinner tether or lower voltage necessary to send power over the tether (future ambition)
  • Less noise generated by the ROV (probably)
  • Less fatigue on the battery tube (as a result of to opening it less to change batteries)




OpenROV simulation
#2

I hope you have a big order in for 2308.65 props. I think you're going to need them.

BTW, although we still have a lot of prop/duct/nozzle testing left to go, there's a big outstanding issue with how to best attach these props to the motor bell. If anyone else wants to help out with this effort, ideas on a good way to attach these Graupner props would definitely be appreciated!


#3

http://www.v-eastonline.com/categories/Graupner-Prop-Shop/Prop-Adaptors/ ??


#4

You could use the 2309.65 prop instead. Its the same prop, just with M5 threads.
You can then make easily an adapter by drilling a 3mm hole in a M5 bolt.
This could then be fastened with loctite bearing glue, heat glue or similar.
The problem with M4 threads is that there not enough wall to drill out the hole for the motor axle.


#5

Very good work!
It would be interesting to see if the efficiency would rise with a bit smaller prop.
A guy on an diy rov forum had great figures with a 50mm prop.but this was on a bilge pump motor.


#6

The conclusions gained from these tests are amazing! I'm glad I haven't gotten a chance to order the props yet for my build.

Have you guys done any testing of the props going in reverse? They seem to be specifically made for going forward, so I'm assuming they'll perform worse going backwards.

Also, I noticed on the website source for the best performing prop, they specified that it was right hand turning. Since I don't know the language on the website I wasn't able to check for a left hand version, but if those are available they could be used on the opposite side of the ROV to eliminate the twisting motion some people are having when going forward.

As always, great work!


#7

We did a little bit of testing in reverse, but were limited because the prop wouldn't hold tight with the attachment method we were using. As you noted, these Graupner props are optimized for going forwards. The bottom line was that the Graupner 2308-65 was about as efficient in reverse as the E-Flight fan was going forwards.

You're right about the counter-rotating props. If there's a counter-rotating set that's available that is reasonably close to peak efficiency, we'll probably go with those. We still have a lot of testing to do, including Kort nozzles and props designed for Kort nozzles. This first day of testing was just to get an idea of where things currently stand- which appears to be not very good in terms of efficiency.

-Walt


#8

Your mention of nozzles reminds me of another question; did you test these props with or without nozzles, because those change the performance of impeller-type props.


#9

Cornwall model boats sell both LH and RH rotating props equal to the best one in this trial.

they also have the M5 props i mentioned in my post below.

http://www.cornwallmodelboats.co.uk/acatalog/propellers_plastic.html


#10

Great stuff to hear!

Do check “Rice nozzles” as well.
http://www.propellerpages.com/?c=nozzles&f=Speed_Nozzle_Tests


#11

Hi Merrick:

We've discussed Rice nozzles a number of times here at OpenROV HQ, but it's our understanding that the US patent for them is still in force for a couple more years. I have no idea what the international patent situation might be. Given that OpenROV is interested in, well, open-ness, we'll avoid Rice nozzles until we're sure the patents have expired.

Please correct us if the information we have is wrong.

So yesterday we spent some time in the test tank working on the low-end side of the speed control. We have a lot more work to do on fine-tuning how the deadband works in the ESCs, but the bottom line is that we were able to get significantly lower thrust levels than is possible with the current software. So we're looking forwards to having a vehicle that not only goes faster, and draws much less power, but one that can also move more slowly as well!

-Walt


#12

Not sure if you noticed these or not, or maybe you are already using them, one of the links below had the props but they also show a number of adapters that insert into the prop and have a set screw to hold it onto the motor shaft.

http://www.cornwallmodelboats.co.uk/acatalog/couplings-modular.html#aC8008

I am not sure how easy it would be to remove the old prop adapter and insert the new one and have it stay securely attached but it looks doable.


#13

Awesome news, and great post.

To ensure I understand the second plot correctly, the x-axis is effectively analogous to "percent throttle" in the fwd direction, right? Because 1.5ms is neutral (or 0% throttle).


#14

I was viewing the YouTube video of you driving the ROV with the new props at OpenROV HQ. I was wondering how you adapted the Graupner 2310.60 props to the OpenROV thruster motors? I would think that everyone would like to make this propeller upgrade.

Also, I noted that you didn't change out the vertical thruster prop. Was that because you didn't have a 3rd prop or was there some advantage with the current prop?


#15

Was this test conducted using the duct around the propeller?

Also I am curious if there is any information regarding peak power consumption for the system as a whole.


#16

Beautiful! This is just the testing I have been looking for. I'd like to try to replicate your results. Is there a US source or equivalent for the Graupner 2308.65? And was the motor a 2213N 800Kv Brushless Motor?

Thanks --Doug


#17

Hi Doug:

Yes, this was with the 2213N motor.

I don't know where Eric got the props for the test, but I've bought Graupner props from Cornwall Model Boats in the UK- link to the props here. If you find a nice US source, please let me know.

Although this blog post featured the 2308.65 props, I believe the kits shipped with 2308.60 props (60mm diameter vs. 65 mm) due to the unavailability of the left-handed props in the quantities we needed to stock the kits. Perhaps Eric can correct me if I'm wrong there. I think OpenROV might have bought out Graupner's entire production run of the 2308.60 props, since they don't seem to be in stock anymore at Cornwall Model boats!

We definitely need to do more propeller testing, and anything you can do to help add to the database would be appreciated. For the last couple of months Eric has been busy in the lab improving the design of the endcaps, and I'm hoping that that process is nearing an end, and in January and February we can do some significant ESC/Motor/Prop testing.

-Walt


#18

Thanks Walt

I you have any recommendations for a set of props you think should be tested please let me know. I plan to be setup for testing in early january. Has OpenROV done any testing with various motors life expectancy in saltwater?

--Doug


#19

You may want to check this link out.

This link has some interesting info and looks like they have tried various props.

http://www.homebuiltrovs.com/mayfair750test.html


#20

Thanks David. Steve does good work.