Car accu as powersource: how to load the best and how to maintain on power while using accu's ?

[Roland]

Thanks Les,

Your 24V 350W motors should work fine. What type of gear do you use? Are they worm gear or straight spur gear? The latter seems to be more efficient. If you have similar payload as mine, balanced heave should be very close to my power levels.

Note that pitch and roll may strain the motors a bit more, since Ian's platform design uses single centerpost weight balance. As the center of gravity of the platform will be some distance above the rotation point, there will be an extra offset force straining the motors during pitch / roll angle. Ian's motion platform software includes a power calculation function that can predict this extra power.

In my design, each actuator has its own weight balance counter force: Therefore there is little power increase during pitch / roll compared to Ian's design.

[iwik]

Thanks Roland,
My motors have a spur gear box built in to the motor assembly.Thanks for loading imfo,all new to me but looking forward to trying it out.
Could you further explain (Ian's motion platform software includes a power calculation function that can predict this extra power.)

Regards
Les

[Roland]

Small correction: Ian has written a small add-on software: Motion Platform Power Estimator. You can run this add-on in combination with BFF 3DoF driver V2.4 and above. It will also run in demo mode.

The software is designed for 3-point platforms with centerpost for weight balance (like the mini platform). It will ask you to enter the platform weight distribution properties (i.e. CG offset in YXZ directions) , you can also tweak the accuracy of weight (im)balance.
You can then let FS generate real-time motion cues, or apply user defined sinewave motion (heave/pitch/roll)
The software will calculate actuator position, velocity , acceleration and force , and derive the mechanical power from these properties.

As an electrical guy, it took some time to get my head around: Ian helped in explaining the basics:

For sine wave motion the maximum accelerations occur when the displacement is approaching and leaving the top and bottom of the displacement - ie as the velocity trace passes through the zero position. The instantaneous power is the product of force and velocity so the power will be zero whenever either the force or the velocity is zero - this will happen 4 times per cycle because the velocity and force are not at zero at the same time. The velocity is zero when the acceleration force is at its maximum, and the acceleration force is zero when the velocity is at its maximum!

I'd say start with a perfectly balanced setup, then apply simple slow heave sinewaves, and see what happens when you increase the sinewave speed. Then add some imbalance, compare the results.
Then do the same with pitch and roll, and see the effect with added CG height. It may take a while before it all starts to make sense, but it will finally help you in understanding power requirements better.

I did comparison with actual heave battery power with my #3 platform design: The actual electrical power drawn from battery differed a bit compared to the mechanical power calculated by the tool (due to driver/motor/gear efficiency, and some other effects not yet fully understood). I will make a comparison again with #4 platform design: it is more efficient, less friction losses, and should thus give more accurate results.

Info and download of the power estimator tool can be found on http://buggies.builtforfun.co.uk/Sim/calculator.php

[iwik]

Hi,
Yes i saw the software on his site but didnt really appreciate what it could do. Thanks for the explanation.
Regards
Les