Actuator placement

[cdoz]

I came across this site a couple of days ago, so I'm still trying to figure out all the intricacies. When I thought about this before reading anything, I thought to put one actuator (I have 2 wiper motors, beefy h bridge etc on the way to play with) each on the x and y axis, but looking around it seems a lot of people are pitting them both on the x in a delta configuration:



What is the advantage of this?

[motiondave]

the diagram on the left would be good for flight I guess.
The one on the right better for race, as vertical bumps feel even.
I had a frame like one on left, a joyrider as first frame, which was good, but bumps felt uneven.
Once I put the motors like on the right, bumps felt right and even.
Depends on your plans for games.

[cdoz]

The platform is attached / pivots in the same place and constrained in the same way for both, I don't understand why one would make bumps feel more even? It seems to me that the one on the right just makes the maths for converting force to actuator movement a bit harder? but I'm sure there is something I'm missing!

[sirnoname]

The first clear fact is that your levers are longer if you connect the motor on the edges. This means less range with same motors but more powerfull with slower movement.
The diagonal calculation will reduce the reachable positions as you have noticed. But I do not think you will use 45° roll or pitch because you motors need much time to reach this positions.

[RacingMat]

hello !

what I can see about this 2 configurations :

- In the case of a pure 100% Pitch mouvement (no Roll), the force is divided between 2 motors (right configuration)
but in the cross configuration, only 1 motor.


But OK,often the mouvements are composed of combined roll and pitch.
And in the particular case of 50% roll and 50% pitch, the 2 configurations look to me identical...

- the lever effect is the same : distance x strength
the distance between the motor rod and the union joint is equal in the 2 configurations


- Why would be the tilt angle different ? I cannot figure out why ...


The question is still pending...
Mat

[RufusDufus]

Hi Mat,

- the lever effect is the same : distance x strength
the distance between the motor rod and the union joint is equal in the 2 configurations

The lever length being referred to by sirnoname is the distance from the point the rod connects to the seat platform to the pivot point (ie draw a straight line between these two points). This distance is greater for the one that connects to the corners of the seat platform and hence the force required to tilt the platform is less given the same load. However because the corners are further away from the pivot point they have to move a greater distance to tilt the platform the same amount - when considering each motor individually. Also the further away from the pivot point the faster you have to move for the platform to have the same rotational (tilt) speed.

You also get similar effect from changing the length of the lever arm connected directly to the motor.

Hope that helps.