Motion Platform Power Estimator

Hi

This might be of interest to other motion platform builders out there. I've written a small actuator power rating calculator application to run as an add-on to the BFF Motion Driver software.

It works for 2 and 3 DOF “conventional” platform designs – those with 2 or 3 actuators under the platform and a central column/spring. Not with joy-rider style cockpits at the moment.

It is beta so may have bugs and I may have to adjust things – take care with the results.

The software runs a fairly simple mathematical simulation of the platform into which actuator position demands are fed. The position demands can be the “live” output from the motion driver software or, perhaps more usefully from a design point of view, they can be pure sine-wave motions generated internally by the software and applied to any of the DOF's. The platform movements are calculated in real-time and the model's equations of motion solved to give the actuator forces required to generate the movements. With these forces and the actuator speeds the maximum duties can be captured over all the actuators and rating ESTIMATES given for a single actuator spec.

The dimensions of the platform can be specified and the center of mass position adjusted to reflect different states of imbalance. The central spring in 3 DOF platforms can be specified in terms of spring rate and mid-position force.

There are limitations off course so if you want to try the software please read over the user manual first. Higher frequency vibration motion will not be dealt with accurately (sample time limitations and limitations of the numerical solution for accelerations), and excessive platform articulation angles will reduce accuracy (keep them to within say +/45 Deg). Note damping and friction effects are not included in the model and actuator inertias are neglected – perhaps in a future version.

Playing with the calculator on different configs and states of load imbalance has really got me scratching my head! However each time I go in and double check the detailed sums the results appear to be correct for the basic model – very eye-opening. Well balanced platforms consume little power – even moderately unbalanced platforms can consume lots, especially when you set the platform oscillating.

Might be helpful for folks designing their platforms. If you try the software let me know if the output looks strange. Note the calculator needs the motion driver software running (v2.4 or later), but it will run with the unregistered demo version (will time out after about 10 mins or so) so you don't have to buy the driver to use the calculator.

http://buggies.builtforfun.co.uk/Sim/calculator.php


Ian

Ian,

That's really an interesting piece of software. Great addition to your driver.

I'll need to do some measurements on my platform, enter the data and see how it goes. I'll try to do some actual actuator power measurements as well to see how the calculated results compare to the measured values.

I just hope the results don't say I have to redesign the complete rig!

Thanks Roland..

It will be interesting to see any comparisons you are able to make.

Note that essentially the calculator determines mechanical output (or input) power at the actuator - it doesn't make any attempt to assess how electrical power might differ from this other than allowing a simple efficiency figure to be applied.

Might need to be carefull of circumstances in which motor current might not be closely related to actuator force.

Ian

Yes, I realize that your calculations are giving mechanical power values. Electrical power will be much more; last time I checked my platform with simple heave step, I found my actuator efficiency was only about 13%. But that was with old H-bridge components, so I expect some improvement here. I'll give an update when I get some results.