Can this be done?

First off i would like to say hi as a new member....I have been trolling this site for weeks now and I envy you guys and your Know in sim building! I have read countless threads here (mostly talltims k8055 )and learn a good bit of the basics, but I do have some questions that are pretty simple but over my head.As far as constuction of a sim I have no problem with ideas and or knowledge to do so but when it comes to the electronics i am clueless.

Here is a link to my first non-motion sim I did a few months ago.
http://www.youtube.com/watch?v=yW03rFpj8Zg

Ok back to the Q&A......
I recently got my hands on a used hospital bed.It has 2 110v gear reduction motors on it with what seems like plenty of torque to do the job. It came with the hand controller and the main unit that drives every thing.It has its own power supply and bi-directional controll via 110v relays.
Upon opening up the hand control unit I have determend that there is one signal wire(one wire with power on it to the hand controller) with a constant 18v ac then two wires for each motor for direction by push button on the hand control. Jumping the signal wire from one motor wire to the other before the relay box....turns the motor in oppasite directions. I guess my question is........ can I use a 8055 and the units relay controller to........ control the two motors? It sure looks possable but i would really like you guys imput on it as I am an idiot when it comes to electronics.....Any help would be awsome....Thanks in advance!

Bump........Do you guys need more info?

bump...as you are using the K8055, may I suggest you message some of the K8055 developers-users on the forum.

Hi Oneshot - welcome to the forum! nice static sim by the way!

almost certainly this can be done, but I don't fully understand your description of the action of jumping signal wires in the hand control unit - for sure we can use the K8055 to control switches with a simple transistor setup, and so get the same action as the hand controls... might be a bit slow, as hospital beds generally aren't supposed to throw the users around in an exciting way, but they should definitely have the power to support gearing!

put together a quick sketch of the connections, and I'll take a look for you...

regards

Tim

PS. Please be aware when bumping that I work 75 hour weeks in a different country from home, so dont have a lot of time to browse new threads... because of this I generally only check the hardware forum threads regularly so copying this question or your connections diagram across into one of the K8055 threads would be really useful!

Hi,

I've not actually yet made my sim, but I've played a lot with the numbers. If your actuators are similar to these http://www.linearactuator-motor.com...tuator_for_hospital_bed_parts_fd1-118176.html then the torque would be more than sufficient (6000N can lift approximately 600kg...), but it's the speed of those actuators that hinder it. 40mm/s is not much, if I were you I'd take a look inside and see if the reduction or the motors could be altered/changed. My opinion is that it would be better if the speed would be at least 4x that of 40mm/s

By the look of that one actuator I assume that the reduction is made with a worm gear (I don't know if yours are of similar construction but I assume so...) Even if the actuators reduction would be reduced to 10 times lower it would still produce 600N and that would still be more than sufficient and the unloaded speed would be 10 times faster.

Controlling those actuators with just a on/off mechanism can be done quite easily, but I'm not sure what the experience riding that kind of simulator would be. If the actuator locks in the position it was when power is removed and the load it bears don't drive it down, then it would need to be controlled with short burst of on/off action and if done with relays would result in quite a noise from them, it would be better to drive them with triacs and some sort of microcontroller.

When dealing with mains voltages safety is the number one issue and it should not be over looked. Isolation of the control signals from mains voltage is essential. Here's one triac drive appnote http://www.google.fi/url?sa=t&sourc...1m5o6-LYw&sig2=ynlcmkcI_HNXKTQ2QM7SXw&cad=rja

I agree with everything you said except this point in bold...

Pulse switching of motors is not necessary to regulate speed... that is only true for the basic pneumatic setup (and I am working on that ).
If we can set up switching using a K8055 and transistor/relay solution to regulate the direction, we could just as easily use PWM to control the speed. With this approach, the relay would make a noise only when you change direction.

This is of course dependant on appropriate components being available.

By the way, I am 150% in agreement with you on the safety aspect... It is absolutely essential to consider the electrical intengrity of any such setup... double insulation of all mains electrical components and earthing the frame would complicate the build somewhat.

Regards

Tim

What I meant by short burts control was that if the motors are controlled with just relays then the motors (most probably of universal motor construction) would turn with a constant speed (depending on the load of course) and as such they would need to be driven into position with that in mind in timely manner, although 40mm/s would not be enough speed if longer (full) travel of the actuator is desired. With the triac solution speed could on the other hand be controlled, but only to slow down the motor(gearing) even more.

Universal motor is kinda special case, as it works just as fine with dc or ac current. One changes the direction of universal motor by changing the direction of current in the stationary winding (field) relative to that of the rotor winding field. There may be two field windings opposing each other in the motor or the change is done in the control relay with just one field winding.

I remember stumbling onto someones site that had made a simulator with vacuum cleaner motors (universal motors) and that may be of some help to you with your quest.

I am absolutely confident that the speed of the motors could be controlled with PWM (pulse width modulation). For a description of how it works check out: Page14/Post9 of the K8055 - Dual wiper motor control with variable speed thread
(or google it )
In its simplest form, you could think of PWM as the ultimate in short burst control... the motor does not receive power all the time, and so slows down between bursts... the longer the delay between bursts, the more it is allowed to slow, and the slower it goes hence the speed control from zero to full power.

This is a really useful description - thankyou for this! :

I guess you would be talking about douwe... it's impressive stuff for sure!

he has a thread on here, and has multiple videos in youtube:

http://www.youtube.com/watch?v=-cpfZHBwvQE

http://www.youtube.com/watch?v=fnRBX51UcN8&NR=1

His website is:
http://jippes.home.xs4all.nl/hi6sim/index.html

Regards

Tim

I kind of know what PWM is as I once thought to make my living as a electrical (embedded) engineer... but then again the world decided otherwise. I lack one year worth of studies, but I'm not so keen on starting my studies again...

But on to the topic, I thought that the original poster wanted a simple control for the actuators and PWM is not as simple to implement in practise without prior knowledge of electronics and power components. Douwe actually has made an amazing job with his controller and cleverly uses 3-phase IGBT bridge to drive 2 motors (could drive a third one), that kind of thing is out of scope for novises.

My other personal interest is CNC and I've made some post on Finnish CNC site. Here's my rambling and ideas for self made servo controller that I'm trying to build http://www.cnc-tekniikka.com/CNC-forum1/index.php?topic=1590.0 It's all in Finnish, but maybe Google translate can give it a go.

Updated first post^^^^^ maybe its more legable:

Sorry for the delay guys I have been really busy with work.....Anyway thank you guys so much for the replies...........Here is a quick drawing to maybe explain what i am trying to work with...... I will do a better one and be able to explain more indepth when I get back to my own pc with some cad software if needed.Lets say all the wires going to the hand controls from the relay box are without power except the purple one.(18v) so if i jump the purple to the yellow I engauge a relay and the top motor moves in one direction. Then I jump the purple wire to the red wire and the same motor rotates in the other direction.And this continues with the same results on the blue and pink wires on the bottom motor. The relay box has a constant 110 volts to it from a standard wall outlet. I am pretty sure this would be a easy connection process but I dont want to burn down the house any time soon lol.
Any help would be great. I think it would be an easy connection but then agin i may be way off! just seems to me That the factory relay board would work just fine? but when it comes to wiring i am a complete idiot.