Self leveling Table

[Rajb]

Hello Everybody,

We are worknig on a Self levelling table. Basically I am trying to build a table which will have a fixed leg in the middle connected with the ball joint to the table top so it will have 2 degree of freedom. This table is 12" X 18" and it will have 2 degree of freedom. The others legs will be connected in a right angle of each other. These two legs will be controlled by dc motor  linear actuator and they will try to keep the surface of the table balanced when the platform of the table will be tilted by +/- 5cm.
This incline/tilt will be detected by inclinometer and I am hoping that some how I can interface inclinometer to LabView, and then the output should go to HB-25 (H-Bridge circuit) to drive the linear dc motor actuator.

I am hoping if you could help me finding the right hardware for this job. Currently our university has NI USB-6251, do you think this will be ok for our project if so then what kind of drivers or interface do we need so we can get the output from the inclinometer to computer and what do i need to interface with dc motor linear actuator so it can respond to that changes to make the table level. Thanks in advance.

Message Edited by Rajb on 09-29-2007 02:27 PM

[Maclean]

Hi Rajb,

You could use your USB-6251 to control the HB-25 with Pulse Width Modulation (PWM), as long as the current requirement is within the specification of the 6251. This however, would be software timed control, meaning it would be nondeterministic and you can't guarantee accurate control. I roughly estimate the latency between reading the inclinometer input and writing a PWM signal to the motors would be anywhere from 3-10 ms. That number comes from some rough tests I did on my computer, not from the user manual, so it is not a guaranteed statistic.  However, it does serve to give you a basis for judgment on whether your 6251 will be sufficient as a controller. If that is insufficient, you will want to use a cRIO chassis, which is much faster, and deterministic.  You would still control your motors with PWM through the H-Bridge and whatever software algorithm you write, but it would be on a Real Time target.

I hope this helps!

[Rajb]

I was wondering if you could tell me what is the maximum output current for DAQ USB-6251. Thanks

[AnalogKid2DigitalMan]

Rajb:

Specs can be found here, I didn't know if you were referring to the analog or digital outputs

http://www.ni.com/pdf/manuals/371291h.pdf