Sensor for measuring Spin Rate/Angle & Velocity/Angle

Hi Andy,

You might want to consider building a software Integrated Navigation System (INS) and use the MEMS accelerometer.  You can set up the INS to sample the changes in all three axis and maintain the running spinrate and veleocities internally.  You compensate for the devices limited measurement space by sampling the data more often.  You can run some calculations to see where your sampling can keep ahead of your objects dynamic rotations.  You might need a DSP to crank the numbers in real time, but you should be able to meet your design goals.

Good luck,

DAB

Hello Andy,

You need to tell us lots more. Is the device free or tethered, are there any power/size/cost constraints. How quickly must the measurements be made. What is the maximum linear and angular acceleration. How accurate etc etc.

Without more information it is impossible to make any suggestions.

Michael Kellett

Hi DAB and Michael,

Many Thanks for both of your replies.  Some more information regarding the specifications:

-Device will need to be free with output via wireless transmission. (RF Transmitter?).

-Everything (Sensor,Power Source, Wireless Transmitter will need to fit inside a space of no more than 40mm diameter).

-Power, due to space constraint I envisiaged be supplied by some sort of button cell battery (1.5-3V?).

-No cost constraints. (Yet!!)

-Measurement will need to be made within approx. 0.03s of initial movement.

-Max. Linear Acceleration - 134112m/s/s (67.1m/s in 0.0005s).

-Max. Angular Acceleration - 3140000 rad/s/s (Not sure if this calculation is correct. I have assumed max. angular rate of 1570 rad/second is reached at the same time as max. linear speed)

-I'm not yet sure about accuracy requirementsbut for now work on +/- 2% on all measurements.

The values above are maximums and maximun linear/angular speeds will not occur together (higher spin rates will have lower angular rates and vice versa).

Any more info needed then please let me know.

Many Thanks,

Andy.

Hello Andy,

13,000 g = munitions ?

No off the shelf mems device will stand 13,000g.

Certainly no off the shelf gyro will !

I'm not at all sure that a button cell will.

Anyway  - this is way outside the scope of Element14 chat - feel free to contact me by email if you like - I used to design accelerometers.

www.mkesc.co.uk

MK

Hi MK,

clinometer sensor could solve all the problems. Pls feel free to contact with me.

www.vigordigital.com

Sunny

@Sunny,

Could you please explain how an inclinometer can measure spin rate or the OP's "Max. Linear Acceleration - 134112m/s/s".

Michael Kellett

Hi,

Having investigated the accelerometer/gyro options, it would seem that there is nothing really suitable to measure/withstand these forces.  I did find one accelerometer which was capable of measuring up to 20000g and withstanding up to 60000g but was single axis only.  I have found nothing in terms of a gyro to measure the spin rate needed.

I am now looking at it from a different angle and considering an 'external' rather than 'embedded' sensing system which can detect/measure the required parameters.  The requirements in terms of what needs to be measured remain as per my previous posts.  I have thought possible ultrasonic sensors or some form of magnetic (Magneto-Resistive?) sensors but not sure if these would be suitable.  Does anyone have any thoughts on this?  The object that I am trying to measure is a golf ball and would like to take all the measurements as soon after initial launch (impact with golf club) as possible.

Any suggestions would be most appreciated.

Many Thanks,

Andy.

Aren't there systems already in existance that will take the measurments you want? I'm sure i've seen them in the higher end sporting goods stores where cameras track the club and the ball and then are able to calculate the forces involved based on the size of the ball, velocity of the swing, angle it was struck and so on. These systems are more for helping a golfer improve there swing but can be used to caculate the forces on the ball.

Trying to cram everythging you wanted into a golf ball probably wasn't feasable to start with. Even if you could get it all in there the ballance and weight of the ball would be effected to the point that the measurments wouldn't reflect real world conditions on a actual golf ball.

Thanks for your reply Michael.  Yes, there are systems (simulators) available.  The issue is that the lower end models, only measure the path/angle of the club (normally with infra-red sensors) and based on that 'estimate' what the ball will do.  This leads to a large degree of inaccuracy.  If you took one of these systems to a driving range and hit a real shot, you would find that there was very little correlation between reality and simulation.  (I've done this so know what the limitations are).

The camera systems are better and more accurate and tend to use a combination of very high speed cameras and infra-red technology to measure both ball and club face.  These systems tend not to measure the spin of the ball but rather the launch speed/angle using the high speed cameras and again 'estimate' the spin based on the club you have told the system you are using and the club data from the infra-red sensors.  Again, this leads to inaccuracies.

The high-end systems that I have seen use either Doppler radar to track the full flight of the ball (these are the ones you may have seen on TV golf coverage when you see a 'tracer' line showing the path of the ball from behind after a player has hit a shot) or possibly laser based systems which use what I believe is termed a 'laser curtain' to measure the ball as it passes through it.  Whilst these system are the most accurate they cost tens of thousands of pounds.

In my opinion, the only important thing to measure in order to accurately simulate the flight of a golf ball is to measure the 'initial' launch characteristics of the ball itself.  These launch characteristics would be the initial velocity of the ball (either in terms of a linear velocity and the angle [X & Y] at which the ball is launched, or the three component axis velocities [X, Y & Z]) and the spin rate/axis angle of rotation of the ball.  From this, using aerodynamic physics, the flight path can be calculated.

So my question remains, might there be an alternative sensor system that could measure these characteristics?

Many Thanks,

Andy.

Hello Andy,

No - there isn't anything that will do this (ie buried in the ball) for less than 10s (more like 100s k£). You are asking for a full six degree of freedom inertial tracking system perhaps 1cm cube size with radio telemetry  - the only other applications for a similar device are military and last time I knew much about what might be going on there they didn't have one either.

High speed cameras are your best bet - if you have a few of them you can measure the intial velocity and spin of the ball.

Michael Kellett