MHz mystic help

[TiTu]

While as a novice fe boater I won't try to guess what the problem is with the op's boat, I had problems with the mhz drives in mystic 114. My issue was too much negative angle which made the boat run too wet.

Iirc Keith offered some modified drive support posts which would have corrected the negative angle, but I liked the look of those original drive support posts so went another route to fix my problem. I made holes in the hull so that the bases of the drive support posts sit flush with the hull. Handling was the same after the fix (I think). I've been using Leo 1600kv motors with 442 props so neutral drive angle is just fine for me.

First image shows the start and last 2 the end result. If you want to read the build thread, its here.

Drive Angle.jpg Fixed drives01.jpg Fixed drives02.jpg

-Titu

[rauldino132]

Nice work

[danielplace1962]

Ok but now people are saying you will need the negative so it don't blow over which I don't doubt. Because I know if you take out the negaitive then CG will need to be moved way forward which is going to do about the same as the negative in the drives does.
Makes the rear end light and you can't even get it to drive away. Then you got people saying you have too much epa. Well ya because if it doesn't have that much rudder you will not be able to even getting it to take off in the direction you areb tryin g to go and you will just do circles and never get it to get up take off and gain speed to go in the direction you are trying to get it to go. The negative like that I already know for a fact induces high speed spinouts because the rear end is not planted but lifted by the negative the drives have.

[keithbradley]

Running 8s in a 45" mystic results in a heavy setup. The heavier your setup is, the more speed it will take to get the hull up and out of the water, hence the low speed "drunk driving" before the boat is on plane. You will experience this regardless of the drive angle. There are two ways to counter it:
1) Lighten the boat. Switch to lighter packs (perhaps 5-6s) and lighter components overall.
2) Learn to drive it. Pop it out of the water and don't fool around at really low speeds. I'm guessing by your posts that this is your first experience with a hull of this type. They are a different animal when compared to wide hulls with flat ride pads. You will become more comfortable as you drive it more. However, based on the video it looks like you either have an issue with the rudder/steering linkage, or improper drive toe. Drive toe can have a profound effect on stability, especially in corners.

Neutral drives will allow for mph maybe in the 60s. 70+ should be an issue on a properly setup boat (in regards to THIS hull).

As far as adjusting EPA and not having enough rudder travel when you need it...This is why we use Exponential steering for these situations. Expo allows finite movement through most of the wheel travel, but enough "throw" at the end to do whatever you need. I personally don't use it, I prefer a linear feel and just adjust my driving to the situation. While it may be difficult not to panic and turn the wheel hard when you desperately need to steer, it's something that you learn over time.

[nata2run]

They DEFINITELY don't need to go to neutral. Trust me, you will be moving them back to negative for sure.
They can be improved by moving them a bit though. If they are too far negative, the boat will be unstable at high speed. As for the cornering, there's something else going on there.

Keith is 100% right, You will end up with a negative on the drives as speed progresses. 3-5 degrees is not uncommon. Looking over the build there are a few things that could be the course. the motors look long, are they the 4070? if so then they are almost too big and mounted way too far forward. Also are the drives 100% aligned to the sharp edge of the sponsons??? and are they at the same negative angle? if one is say 10 degrees as you mentioned and the other is 7, then not so good! where the drives exit the sponsons, are they mounted in the same exact mirrored spot? (don't assume because it looks to be right) all those things can have a negative effect on the handling and general performance. definitely those tubes/water pickups gotta go, Its like a second rudder. With the cornering, a couple of things... motors not in sync and turns the boat before the other kicks in? drive slightly misaligned pushing the hull to one side at low speeds. Heavy on one side, or cables grinding in the tube causing loss of performance in one motor. Or .... those water pickups. Remember, everything that runs as a twin must be mirrored the same way. Both sides must be a close to identical as possible. A bit like if you have a bruised leg, you will have a limp.

[rauldino132]

Yes they are 4070 motor that's what was recommended to me and I will check up on the other things you mentioned thanks guys for all your help

[iridebikes247]

As Kent said everything must be in sync. Make sure all batteries on the right side have the same ending voltage as those on the left. Sometimes one esc will have a different startup setting and can throw things off.

Considering the size of lehner 2250s and other setups that have been run successfully in the mystic I think the 4070 works. As far as the whole going neutral nonsense goes, you WILL need negative over 80 mph or maybe before that.

I've been driving the mystic for 3 seasons now and if I haven't driven in awhile I have to relearn driving it at low speed. It will always look like a fat kid trying to run cones at football practice at low speed, once its on plane things change quickly.

[nata2run]

When I mentioned 4070's being on the big side, it's simply because of weight! Yes 2250's have ran In those successfully, but they are also on the big side. You only run those because you need the power to go fast, and you take a few compromises by installing such a "big" motor. If 80 or 90mph is the goal, then a lot less will do. The fact that those big motors are that far forward, also changes the weight distribution a great deal. It's not just about CG, it's very important where the weight is planted. For those fast cats, they like the heavy motor weight in the A$$ so to speak.

[iridebikes247]

Not my boat but this guy took some good pics of his boat in the build process, shows how low the flanges are and everything still bolts up. Mine are just as low I'd say. If its a real problem, installing a 2mm transom doubler gets you away from the rounded part of the bottom of the hull making tightening easier, if its an issue.

As Kent said, definitely sacrifices when you go with a powerful setup in this case handling because of weight. The handling is messed up but weight might be exacerbating the drive placement problem in a big way.


mystic.jpg

mystic 2.jpg

[danielplace1962]

I have a MHz mystic cat 44.8 running tp motors and swordfish esc and x447 props The problem I'm having is the boat runs straight but in the turns it seems to spin out and to get it to go straight again it's a little challenging does anybody have a Cg were it should be set up at or the props should be spending out or in.right now I have them going in any help would be grate here is a video http://youtu.be/n-yFOR6Fzso

All it took was spinning the props the other way which was basically what Raul's post was asking from the beginning. Spinning them out fixed it almost entirely.

Boat is 90% cured. A little more trimming and some more driving practice and it will be doing pretty well.

Anyone know a good 3 blade Propshop UK #'s for these 4070 motors running 8S each.

Wind was kicking up pretty good so wide open would have required a little adjustment. He wound it out before I had the camera once or twice and it was hauling pretty well. https://youtu.be/7kwiZrXDd5Y

[nata2run]

I would not recommend a 3 blade prop on this boat at all. If you want more speed than what you are getting slowly work you way up with some modified larger props, say 457 reduced to 48 or so, but I would try some inbeween sizes first before you get into that. And yes, spinning outward on the props is an easy fix for up to 80 mph, once you go past that, you have a totally different boat again. If the boat is not handling well with the props spinning in, you should definitely work on that part before you branch out with lots of different props.

[iridebikes247]

Should handle very well with props spinning in too. Prop direction should not make or break this boat when only going 75 mph. Props, stay 2 blade but something tells me you've made up your mind on them already anyway

[rauldino132]

Should handle very well with props spinning in too. Prop direction should not make or break this boat when only going 75 mph. Props, stay 2 blade but something tells me you've made up your mind on them already anyway

No just seeing if there something better then what I have now