- #1
RacerDad22
- 13
- 0
Hey All,
we race mini / kids ATVs at a national level. these little things use a CVT style transmission, which is critical for performance, and tuning is a pain. if you are not familiar with a CVT, the fundamentals are a spinning mass on the crank shaft that creates a force on a part called a variator. that force is transferred via a belt to a rear pulley, where a spring is used to resist that force. when the force of the spring is overcome by the force of the spinning mass up front, the CVT begins to shift.
The problem at hand I am trying to solve is balancing what weights up front to use, at what RPM to overcome what force on a chosen spring. ultimately, I am looking to control the shift point (rpm) at which this begins, and get the process as linear as possible. I have taken some measurements of various spring rates and force it takes to compress in lbs. I also have the radius distance of the weights against the rotating front variator. here is an example of what I have calculated:
spring "A"
initial compression length 1.75 inches =89lbs
mid point compression 1.5 inches = 96lbs
final compression of 1.25 inches = 114lbs.
variator force -spinning weight =18g, distance from center of variator to center of weight =21mm measured force in lbs:
7000 rpms =46lbs
8000 rpms = 57lbs
9000 rpms = 75lbs
10000 rpms = 93lbs
11000 rpms = 112lbs
12000 rpms = 134lbs
13000 rpms = 157lbs
so, here is where the measured and observed differ. from looking at these numbers, spring "A" should not begin to shift until somewhere between 9000-10000rpms. in reality, it begins to shift at around 8000 rpms.
anyone got what I am missing to put into my calculations? some thought I had, but no sure about:
*is there any other force put on the rear spring besides the rotational forces? the belt connecting the front variator (weights) to the rear pulley does have a ratio to it (small front to larger rear), but is not calculated for in my equations.
*measuring the front weights - the roller weights are cylindrical and in a ramp inside the variator part. I measured from center of the variator to center of the weights. also, the weights are on a ramp that "rolls" the weights to the outside of the variator at a given rate. so if initial distance is 21mm, the final radius is something like 29mm - I have not measured that.
-EA
*
we race mini / kids ATVs at a national level. these little things use a CVT style transmission, which is critical for performance, and tuning is a pain. if you are not familiar with a CVT, the fundamentals are a spinning mass on the crank shaft that creates a force on a part called a variator. that force is transferred via a belt to a rear pulley, where a spring is used to resist that force. when the force of the spring is overcome by the force of the spinning mass up front, the CVT begins to shift.
The problem at hand I am trying to solve is balancing what weights up front to use, at what RPM to overcome what force on a chosen spring. ultimately, I am looking to control the shift point (rpm) at which this begins, and get the process as linear as possible. I have taken some measurements of various spring rates and force it takes to compress in lbs. I also have the radius distance of the weights against the rotating front variator. here is an example of what I have calculated:
spring "A"
initial compression length 1.75 inches =89lbs
mid point compression 1.5 inches = 96lbs
final compression of 1.25 inches = 114lbs.
variator force -spinning weight =18g, distance from center of variator to center of weight =21mm measured force in lbs:
7000 rpms =46lbs
8000 rpms = 57lbs
9000 rpms = 75lbs
10000 rpms = 93lbs
11000 rpms = 112lbs
12000 rpms = 134lbs
13000 rpms = 157lbs
so, here is where the measured and observed differ. from looking at these numbers, spring "A" should not begin to shift until somewhere between 9000-10000rpms. in reality, it begins to shift at around 8000 rpms.
anyone got what I am missing to put into my calculations? some thought I had, but no sure about:
*is there any other force put on the rear spring besides the rotational forces? the belt connecting the front variator (weights) to the rear pulley does have a ratio to it (small front to larger rear), but is not calculated for in my equations.
*measuring the front weights - the roller weights are cylindrical and in a ramp inside the variator part. I measured from center of the variator to center of the weights. also, the weights are on a ramp that "rolls" the weights to the outside of the variator at a given rate. so if initial distance is 21mm, the final radius is something like 29mm - I have not measured that.
-EA
*