Miss Geico Race Prep

[Darin Jordan]

Hey Guys... Bailed on work early on Thursday, Friday, and also ran down to the lake on Saturday morning, to test with the Miss G. The Eagle-Tree got a real workout...

Unfortunately, I was only able to make the airspeed sensor work for one session. It otherwise would not record, and seems dead now, so I'm looking into getting the GPS module...

However, it did capture a couple of pretty impressive runs...

Both of these were done using the stock motor and ESC. The only mods to the boat are as posted here: the offset rudder and the truing on the sponsons, and the upgraded contacts on the motor/ESC.

DISCLAIMER: Don't try this at home... the amp draw was WAY above the ratings for the ESC. Please keep in mind that it's part of my deal with ProBoat to test the limits, so that's what I was trying to do...

The first graph is from immediately after plugging in. I ran the motor up unloaded for a moment to get a baseline for the motor KV recorded.

The second is a clip from a 2-pass run using a Prather 230 prop. I have another graph where it shows 49mph max with this prop....

The third is a from a run of several passes using another prop. Going to keep this one to myself for now. It works really well, and I want to play with it some more. I ran the boat in a simulated Offshore run for about 2.5 minutes, and it was breaking 40-MPH regularly. During another test... ran an average of 44-MPH with a peak of 46... (See last pic...)

I may have some video to post. We'll have to see if any of it turned out.

I REALLY like this boat!

[tiqueman]

Uh oh.. keeping secrets like the guys I used to race cars with.

C-mon, do tell!

[Darin Jordan]

Uh oh.. keeping secrets like the guys I used to race cars with.

C-mon, do tell!

Nope... I told you the fast one... the Prather 230 was straight up, just sharpened and balanced... The other one was a custom piece that most wouldn't be able to duplicate anyhow, and would likely burn stuff up without having the work done to it.

I haven't calculated the speeds yet, but I also tested with an Octura X645 that has been pitched up slightly, and it REALLY worked well... I'll try to get those numbers worked up and post them tomorrow. That one had really good handling characteristics as well....

[tiqueman]

I ended up w/ an M445 on mine and swapped the esc for a T-120. ALL of the bounce is gone and its running well on it. Temps are staying just over 105 for sport playing. Havent got it out on a lap event yet.

Feel free to PM me the worked prop info...

[Darin Jordan]

I ended up w/ an M445 on mine and swapped the esc for a T-129. ALL of the bounce is gone and its running well on it.

I'm still working on the slight porposing part... Haven't shaken it completely yet, but haven't really tried yet either... I'll have to go back and read through all your threads to figure out what you guys are doing to get that smoothed out.

It feels like the hull may not be packing quite enough air for the speeds it's going, which may be contributing to this. I noticed that, when a slight wind kicked up and the water rippled up, it all went away when the boat loosened up. I'm running dead neutral right now, with the strut basically setting flat on the setup board, so the centerline only slightly up from the sponson bottoms. Need to modify the strut a bit to get it any higher up.

[tiqueman]

My strut is neutral and sits such that the backs of the sponsons are not quite and eighth off the table. well one side differs from the other a bit... I think shes got a lil twist in her. A 642 and 640 still bounce w/ this set up, for whatever reason, the M445 doesnt.

[LiPo Power]

Sounds like the M445 and the secret prop Darin is using are the way to go!!!

[Darin Jordan]

Here is some more data:

First, based on the graph I posted previously with the unloaded motor setup, the motor KV calculates to be 1522KV. This is with the ESC set at HIGH timing. This baseline is useful in seeing how much the system drops KV under load, which can give one a good idea of how different props are going to perform or affect the system.

Also note that the battery voltages. As you will notice, the average voltages vary. If some of you aren't getting good results, your cheap batteries may be to blame. Some of the props can REALLY draw cells down.


So, in the first chart, I made a run using the stock Miss Geico plastic prop. Using the average RPM shown, and a figure of 2.52" pitch (Prather 215 listed pitch) with 25% slippage, the calculated speed would be 34.32mph. Average amp draw was 53.73A. Sounds about like what others have achieved. Speed would have been a tad faster if the batteries had been fresh for this run. As you can see, the voltage is down around 14.14 under load. I ran several tests back to back, so this pack had been run for a bit.

We can compensate for this a tad, by calculated the effective KV, using the existing RPMs and voltage, then extrapolating to estimate some speeds... Doing that for this case, 19114.87/14.14 = 1324KV (under load). On a fresh charge, voltage would be up around 15.5V or so. Using this figure, would could estimate that 15.5V x 1324KV = 20533RPM (which is what I've seen on previous test data for this prop setup... ) This would translate into around 36.85 MPH in stock trim.

Second chart shows the same setup, using a stock, untouched ProBoat Stiletto prop. Batteries were a little bit fresher for this one. Speed calculates to 37mph. Amp draw was 46.19A. Better prop, less flexing, more efficient. Makes sense. Estimating on a full charge: 20592.10/14.90 = 1382KV (see a pattern forming here?? ) 1382KV * 15.5V = 21,421 RPM. This would translate into approximately 38.46 MPH.


The Third chart shows the same setup, this time with an Octura X645, full bladed, but with the trailing edges bent up a tad (pitched up). I haven't measured it to find out exactly where it is, pitch-wise. I'll try to do that in the next day or so. Stock pitch is 2.835". Based on the chart, this props loads down the system more. Loaded KV dropped to 1289KV. If using the stock pitch numbers, the chart would be showing around 36.87MPH. Estimating using the loaded KV, the speed at 15.5V would be 40.357 MPH. Again, my X645 has some pitch added to it, so I'd estimate the speeds in the chart to actually be somewhere more in the 39-41MPH range... I'll try to measure the pitch exactly and recalculate. Amp Draw is a little beyond what most should probably be running on the stock ESC...


More to come as I gather info...

[Darin Jordan]

Sounds like the M445 and the secret prop Darin is using are the way to go!!!

According to the information I'm gathering... Using the M445 (stock), the speeds would be in around the 36-38 MPH range... The M445 actually has less pitch than the stock Plastic or Stiletto prop. 2.478" vs. 2.52" according to the prop chart. The extra blade area of the M445 may be helpful, and it's "pre-detongued", so that's killing some of the lift, which may also be helpful....

If people have info to the contrary, please post it... I'm using a figure of 25% for the prop slip, and this obviously isn't the same for all props. I'm thinking the larger blade area/diameter props would have less slip. I'd like to understand this better.

[Darin Jordan]

I also tested an ABC 45x55 and LOVED the way it handled. The boat flew on this prop, but I'm having trouble estimating the speed, because this prop is listed on the prop chart at 2.165" of pitch, but there is NO WAY it was only going 30 MPH... (calculated).

The pitch chart is the AVERAGE pitch across the entire blade... I measured a Prather 230 and from the trailing edge to about the midpoint of the blade, this prop shows around 3.4" of pitch... Chart has it listed at 2.992... I need to measure the whole blade to see how the actual chart and prop coincide.

I suspect that the 45x55 will measure out to have a bit more pitch in the half of the blade that the chart would indicate. Also, I may have bent on this one a bit in the past... I can't remember! (ANOTHER reason to start measuring these things for real!!

Here is the chart from the 45x55... I'm positive it was into the upper 30's, low 40s... the amp draw would indicated this kind of speed as well...

[ron1950]

first off i know nothing of amp draw etc that said how do u think the stiletto motor would do in the mg? i know run time may suffer but what do u think speed wise? better or worse? thanks for the info on the mg love to read this thread now.

[Darin Jordan]

first off i know nothing of amp draw etc that said how do u think the stiletto motor would do in the mg? i know run time may suffer but what do u think speed wise? better or worse? thanks for the info on the mg love to read this thread now.

It's all going to depend on the prop... If you are talking simply swapping motors, using the stock prop, I would expect the 1800KV motor to be good for another 3-4mph...

[ron1950]

thanks darin ..... it seems to be just that (2 or 3 mph faster) then stock friends boat....useing detounged x640. bateries seem to drain much faster then stock though lol....probably go back to stock and try some of your upgrades soon though.....oh ya.....the retrival duck works great lol

[Darin Jordan]

thanks darin ..... it seems to be just that (2 or 3 mph faster) then stock friends boat....useing detounged x640. bateries seem to drain much faster then stock though lol....probably go back to stock and try some of your upgrades soon though.....oh ya.....the retrival duck works great lol

That's the trade-off for sure... 2-3mph is actually quite a visual difference on the water, however...

What I concentrate on a lot more is acceleration out of the corners, and speed through the corners. A GPS reading of 45mph doesn't do you any good if it takes you the length of the straight to get up there.... I'd rather hit 43 or 44 by mid-straight, and carry that "slower" speed the rest of the way to the next corner!

[LiPo Power]

After reading it all here I made my move to do the rudder mod before the season.
Here is some pictures of wicked outcome and funtastic job I did
Robert