For the latching relay I use a (MX016 - 1 Ch. Relay Card Module) from Qkits. There nice in the fact that they can be chained, but I won’t need to do that in this application. The keyboard will use 2 SPDT limit switches with 2 DPDT relays. One for forward and one for reverse. The limit switches when tripped will break the latch on the second pole in the relay and vise versa. The limit switch when un-tripped it will allow the apposing relay to latch. I think this process is called basic ladder logic. Yes I might have to slow the gear motor down a bit, but it looks so much like the right speed seeing it turn. The sprocket is thirteen teeth and 1 and 1/8 in diameter and 6rpm. Six times faster than a minute hand on a watch. The chain is 23 inches long, looped 11 and a half inches of travel. 6rpm X 1 and 1/8 inches. So if I’m right that would be 6 and ¾ inches in one minute. I’ll have to wait and see.
I think you've made an error in your calculations. You based everything on the cog diameter not it circumference (distance around the outside edge). For simplicity I am working in metric... sorry. Cog Diameter: 31.25mm Circumference: 98.17mm This means it can move 98mm per minute. Not very fast really. That would probably take a couple of minutes to move your draw out. I'd guess you'd want it faster. So if your draw is to be displaced 300mm in 3 seconds (any longer and I'd get fed up waiting) the cog must rotate at a speed of 61rpm. Working: 300/98.17 = 3.055 Rotations needed to move distance 3.055/3 = 1.018 Time modifier. The 3 is for the 3 seconds we want it to move in. 0.5 second would result in 6.11. 1.018x60 = 61.11 Time modifier. Convert revolutions per second into revolutions per minute. Formula: 60(lenght/(time x cog circumference)) HTH
Motor speed No Problem on the metric. Now you got me tinking! I will set up the chain and the idler sprocket and make a mark and time it. I might even make a short video of it and post it.
Ok, I should be ok but it is a little slow. 21 seconds to travel 11 inches which will be the width of the keyboard. I made a video of it and saved in Windows Media Video format. Note I put a screw in the chain so you can track its movement. No AVI format – I can only save it at 11 Megs for 21 sec and I don’t want to waste space on sever. I could always change the sprocket size later. Maybe I’ll stop at the Tweeter big screen store to have a look at there big screen that pops up out of the box to see how fast it moves. Also I repacked the gear box with heavier grease to cut some of the noise. If noise is a problem later I will cast a foam cover. (The 2 part mix type of foam) http://home.comcast.net/~johnsreb/Gear_Motor_0001.wmv
guess that could be bareable (i can be very impatient) I would make it faster - a bigger cog would solve that, you could locate the motor away from the actual kb tray by having the chain run up the back of the desk... could help with noise as well..
Yes I can buy a 25 tooth sproket, but I'll waite and see first I really don't have the front part of the desk built yet and I just bought some extra chain for like you were saying move the motor to the back. Once I have the front built I can then hold the parts in different spots to find a good mounting spot. More than likely, right up the center is what I want to go for. The size of the motor would interfear with the keyboard at 11 inches distance. I would be looking at 2 to 3 inches longer.
Project is on hold The desk-mod project will be on hold for now. My father has cancer and with then 9 hour trips to see him in an other state, its been tuff. As soon as things get back to normal I will be posting more.
Sorry to hear about your father, man. Thoughts are with you. Sod the project for now - we all understand family is more important. Best regards, John
