Wednesday, August 10, 2011

Input needed

Okay, to all the M2 owners out there...

My push-rod wand mechanism is different from the Mach2. A couple of pix are below and the relevant dimensions +/- are as follows:

Rod attaches 30 mm from the pivot point and results in a 34 degree swing in the wand to achieve the 24 mm horizontal throw at the bell crank.

Wand length is 92cm fully extended (vertical distance below the bottom of the hull when vertical) and 74cm when shortened up (as it was this past weekend)

The ride height adjustment simply lengthens or shortens the push rod and will cause the max flap up wand position to occur either with the wand vertical (high height) or at a bout a 45 degree angle (low ride height.)

Am I in the ballpark???


Phil Stevenson said...

The movement stated seems like a lot to me but it all depends on the bellcrank ratio and how far aft of the flap hinge the vertical pushrod acts. If you have a 1:1 bellcrank and the pushrod is less than 25mm, then your flap movements would be excessive.
I have a similar arangemet at the wand end and I am sure my pushrod attaches much closer to the pivot.
I also note that due to the large offset your pushrod needs to bend a lot when the wand is back, makes for a lot of friction in the tube and potential to damage the pushrod in crashes. Better to add some sort of universal joint, cut the rod and bind and glue on a splice of vectran outer leaving only a tiny gap between the rod ends. It only needs a few degrees movement.

Tim said...

Your setup is much more like a Bladerider than an M2. If your bellcrank/flap setup is also like a BR (i.e. as Phil says) then yes you will have far too much flap movement, i.e. you will have too much gearing overall. I've been trying to lower the gearing on my BR (mainly by shortening the distance between control rod attachment point and pivot) but I think there's another factor - the angle between the attachment point to pivot line and the line of the wand itself. This is because you get max gearing from the wand when it is vertical (greatest change in wand block angle from a given water level change), but in your setup you will also get max gearing from the attachment point to pivot position since this line is almost vertical as well (greatest rod movement from a given change in wand block angle). Because these two effects coincide for you, when you're at max ride height with the wand almost vertical the gearing will be huge and it will be like sailing over speed bumps. From memory on the BR the offset angle is around 30 degrees which is better but probably not enough. Finally an alternative approach to fix the rod friction problem would be to use a BR style short attachment arm. I hope this helps and makes some sense!

Joe Bousquet said...

I haven't touched the M2 bell crank so whatever is "stock" is what I have. I assume if the two arms of the bell crank are equal length the the ratio is 1-1. I did measure the horizontal movement of the ball on the bell crank and got the 24mm (obviously the ball moves in an arc, so the straight line distance is an approximation.)

Phil: you said the pushrod should be moving more than 25 mm or I have excessive flap movement. I'll try to lengthen the ball arm and shorten the arm connected to the flap. I suppose this would decrease the gearing as Tim suggests.

I like the articulation idea at the front end. I'll try it on a spare pushrod.

Tim: the wand angle obviously comes into play. I suppose the best set-up would to always have the wand near vertical at max flap up. This would not be possible by a simple ride height adjustment, but would require the wand length to decrease as the ride height lowers.

Thanks for the input, it's off to do some experimenting...