Need help for a design

Help & Support Robot Parts
1

Hello forum,

I’m new here and I’m new to using motors and doing mechanical things. I’m more into electronics. I would need help to find a motor and driver board that fit my needs. I want to design a linear actuator that would move a light charge up and down. I’ve made a 3D sketch to try to explain my idea.

https://www.robotshop.com/forum/https://img15.hostingpics.net/thumbs/mini_188195design1.png
hostingpics.net/viewer.php?id=188195design1.png

https://www.robotshop.com/forum/https://img15.hostingpics.net/thumbs/mini_691019design2.png
hostingpics.net/viewer.php?id=691019design2.png

The blue is the motor and the yellow is where most of the electronics will be (H-bridge, battery, SBC, etc.) The motor will be coupled to a 1 meter T8 lead screw (gray) and the screw will guide a polycarbonate tube (lightweight, around 200g if I’m not mistaken, length between 80 to 90 cm). the green part below the polycarbonate tube will be a led and its battery. The whole design will be contained in a stainless steel cylinder not shown here (or PVC or something else, I dont know) to hide everything when the moving part is low.

Concerning the motor I thought about this one, which is supposed to be kind of a portative drill if I understood correctly. To control the motor I though about this with a raspberry pi and the GPIO pins for prototyping (I have the raspberry pi 3).

My biggest question is on the motor. It has a plus and a minus pin, so at first I though you couldn’t reverse the rotation but it seems that you can but the motor will be less effective. Did I get that correctly? I want my load to be moved up in few seconds. 1 to 2 seconds would be ideal, is that possible ? With a “4 start threads” screw the load will move 8mm per revolution, so a 80 cm travel in one second would need 100 revolution = 6000rpm ? Can I use this motor ? Are there more appropriate motors ?

The “stall current” is 43 A, the driver board is limited to 3.6 A. The voltage will drop, the motor will stop, and nothing will break or heat up too much if the resistance against the rotation is too high ?

The enclosing cylinder will guide the movement so I’m not worried about the bending of a lead screw that long and the constraints on the motor, maybe I’m wrong ? I thought about a mechanical stop to control the length of the travel for the screw.

For those wondering what it is supposed to be, it’s like a lightsaber but with a very long hilt so I would need a compact design to be able to hold it. The polycarbonate tube has a 1 inch = 2.54 cm diameter.

Sorry if some parts don’t make sense, I’m not a native english speaker and I’m not sure about some technical terms.

Thanks for your help !

2

30 views, no answer : I will try to be more straightforward with my questions.

1 - Can the selected motor spin both ways ? I would guess yes but with a decreased efficiency with inverted polarity due to the “brushes being moved to the opposite side of the normal neutral plane”.

2 - Is the driver board usable with this motor and my requirements ?

3 - I’m trying to understand how much a 500g-1kg load on the lead screw will affect the rotation. How can I translate this weight to the torque (g.cm) ? Trigonometry knowing the diameter of the screw and the pitch ?

Someone know the equations related to the figure on the motor page ? I extrapolated from the “I” curve (having 25 A - 4000 g.cm) that 3.6 A could give me a maximal torque of 591 g.cm (with 0.65 A at 0 load). At 591 g.cm the speed is higher than 6000 rpm, the efficiency is near max, the output power is around 40 W, hard to tell but more than enough for the needed power of 10 W (for 1kg, the force being 10N and the power = force (10N) * distance (1m) / time (1s)). I need to understand what output force would I need at start-up to beat the inertia, because the calculated power of 10 W is not the peak power.

Maybe the easiest way to figure out if it will work is to buy and try… I think I overestimate the load I have to move. The polycarbonate tube is between 150g to 200g. The screw and led are, I think, negligeable and the battery for the led I don’t know but not so heavy that it will go over 500g. An AA battery is around 25g. Maybe friction will play a big role ?