MHz mystic help

[rauldino132]

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

[ls1fst98]

How much are you actually turning it?? They are fairly long n skinny hulls and will hook and spin out with too much steering input. Any play in the rudder linkages? In the video your friend says you may have had an issue with an esc not turning the motors the same?

[rauldino132]

The speed is 30% and The throw I would say about 3/8 to 1/2 from neutral if that helps

[Heath M]

Turn the steering throw on your Transmitter down 10% at a time as maybe the problem. To long a rudder could also cause the boat to hook like that. COG want to be 30 - 33 % of the total wetted length of the hull.
The boat won't like quick sharp turns either.

[Tomcandersen]

The thing is that this hull I made for high speed and at low speed its normal that one of the "hulls" falls through and this happens. Specially when go from 0 to 30mph. I have the same hull and it happens to me as well, not that often in turns but from 0-30mph..

[danielplace1962]

Raul,
We know one major issue. Because the drives have 10° of negative in them even after machining the jack pads to the minimum and still have a set screw to hold them together.

Until the drives are fixed I doubt it is going to drive even then these hulls still do only one thing. Go fast in a straight line. Doubt your going to heat race with it. ???

[kfxguy]

I've had boats spin out from the rudder being too short and from too much weight up front

[danielplace1962]

The rudder is full length machined custom scale rudder that has never been cut. Would be a project to get a longer one.

Even with the excessive negative that is in the drives the boat pulls the front end up pretty good when the power comes on so moving the CG rearward would not be good or even possible because as they back against the motors now.

We have only tried on set of props and have them running inward. Going to try outward next outing. Want to get the drives fixed so we cab get them flatter but then the batteries will need to go forward or it is just going to blow over.

[iridebikes247]

These boats can turn

https://www.youtube.com/watch?v=uAObTBvBOGk

I don't think negative is the problem, looks like way too much steering input.

[danielplace1962]

You know that those boats are running with 10°'s of negative in the drives of the boats you posted ?

I realize it looks like just to much rudder throw but unless you have a bit in it you will not get it out of the water to go anywhere. You will do circles.

The touchiness is a bit of the driver also the problem isn't at speed like the video appears to be showing it is the slow speed getting it going again straight once the hull has settled. You can see the back end lift and the props push the rear sideways. At least that is what it looks like in person in addition the forward CG which we can do nothing about in addition to major negative drive angle that you can't easily do anything about.

Crappy phone video and short but this is the boat. https://youtu.be/2D2iGM24rQc https://youtu.be/oolzbAWynIk

It would start better and turn better if the CG was back but we are running 8S on each side and with the CG where it is with both packs back to the motors in addition to the negative the slow speed handling is hard to get started.

It turns great at speed on 4S per side and it actually turns just fine on 8S a side when the speed is there but trying to take off is a challenge to get rolling straight. The high speed wideouts were just Raul letting off too quick. You can go 70 then lockup the props. It is like full left with a hydro as your going to leave the water.

We have set the epa's to almost nothing and while it surely will make it drive easier at speed you will never get it to even take off and go if you don't have enough throw to get it turned around and drive it straight until it gets up and goes.
We used exponential also to make in less sensitive and catch up near end of travel. It isn't the steering. Turn it down and you will do circles before and never get going straight.

[rauldino132]

Raul,
We know one major issue. Because the drives have 10° of negative in them even after machining the jack pads to the minimum and still have a set screw to hold them together.

Until the drives are fixed I doubt it is going to drive even then these hulls still do only one thing. Go fast in a straight line. Doubt your going to heat race with it. ???

heat race what's that?? lol

[danielplace1962]

It is what we do every Sunday in the cooking SF sun. You know HEAT racing.

Ok, I meant chase the other guy around the buoy's.

[keithbradley]

For what it's worth, the hull you guys are talking about currently holds the S-cat (8s) IMPBA world record for 1/3 mile oval, so while there are hulls better suited for oval racing, it certainly CAN turn.

If the CG is too far forward with 8s, I would say the motors were placed too far forward in the hull when it was built.
I don't know how or why you would possibly have the drives at 10 degrees negative. I think you need to post some pics of the build; that's likely where the problem/solution lies. It's very hard to diagnose from the video, although it definitely doesn't look right.

[danielplace1962]

The drives are at 10° negative because the jack pads are too tall you cannot take it out. They have already been machined down to the maximum and they still have negative. It already had 1/8" machined off them because they were at a 30° negative with them the way they come. I mean pointed at the ground negative. The drives themselves needed to be lower and more inside on the transoms but even still there is no way the setup as supplied would ever be able to adjust out the negative they have in them. There are many threads with people having this same issue.

The drives that are made for the boat have a issue. You can not collapse the jack pads to get the negative out. It is a common issue that they have. It isn't anything new it is a problem most have until you find a way to fix it. New custom pads that are inside the hull and are flush so the drives can be raised flat or something.

The motors and mounts are all made custom from MHZ for the boat and you can't really move to motors back any further than they are. At this point it needs custom made pads machined to get the negative out but then it is surely going to need the batteries moved way forward or it will be upside down the first time the motors hit. Until the negative can be adjusted out it will likely not handle at low speed and be susceptible to spin out while corning at speed.

[ls1fst98]

If it's balancing at 30%, you shouldn't need to move the batteries any further forward.