Motor suggestions for my Space Blaster part - Page 1
Forum section: electronics / projects

author: Youkai
author_rank: Regular Contributor
timestamp: January 13, 2024, 04:28:03 am
content: I'm working on a project "Space Blaster". The part that matters here is the shell at the end of it. The shell is a 160mm diameter tube that I'm going to print probably 2-3mm thick. The last 40ish mm of the tube is going to be split into 4 segments. This section needs to do something like what is shown in the video.My thought was to print a ring that moves which has the 4 sections mounted to it. That would be mounted to the "core" on some bearings. The core would have some cam-tracks for a lever attached to the moving bits. This way the open/close would be purely mechanical as it rotates.Then the moving ring would have a printed gear around it and I would mount a motor to the core to mesh with it. I would set the motor up to rotate the ring 100 degrees or so.The question is what's the best motor to use for this? I think I basically have two options. 1) a DC motor with a lever switch at each end to control the extent of travel. 2) a stepper motor with a lever switch at the "closed" end so I can get a reference point when powered on.This will be controlled by an Arduino microcontroller and run off a battery pack. So size and power consumption are both considerations. Given that what suggestions do you have for the best way to achieve this? I'm not sold on this design if you have a suggestion of a different mechanism that would work better. Thank you.https://youtu.be/cYuv4BxF3Vg?si=76mImC4k1KxlXS8r&t=12

author: coromonadalix
author_rank: Super Contributor
timestamp: January 14, 2024, 03:39:43 am
content: something cheap as this oops my drawing sucks for the closed position lolla small driven motor with a gear box / reducer with position detection or stepped motor or motor with optical wheel etc ... with 4 small leversyou choose the right circular motion disk size, lever lenghts etc ... mechanically simple and wear tear proofno need to over complicate things with turning rings, just need to monitor the start and end position ? optical coupler ...

author: Youkai
author_rank: Regular Contributor
timestamp: January 14, 2024, 10:35:46 pm
content: I don't understand your drawing. There are two motions that need to happen. The four quarters of the shell need to hinge open. Separately the whole "block" of 4 quarters needs to rotate around the central axis of the tube.Your drawing seems to maybe address the first issue. But the first issue is the easier one. It's the rotation around the axis that I'm trying to find an appropriate solution to. Specifically what is a good servo / stepper / motor to move it.I need the device to have a maximum dimension around 40mm (probably, not sure how much space I have yet) and to be controllable via arduino or breakout board.

author: Ian.M
author_rank: Super Contributor
timestamp: January 14, 2024, 11:15:44 pm
content: Small stepper motors aren't noted for their high torque. This could be both a good and a bad feature - if something external jams rotation, provided the coupling is adequate, the stepper will stall without damage, but OTOH without a rotational position sensor, the controller has no idea the stepper has stalled and the rotor is out of position, so the user must switch off and correct that manually.Personally I'd use a position sensor and a DC motor (probably a gearmotor) and simply run it till the position sensor pulses. The position sensor would be designed to output four pulses per turn, one at each position the rotor should stop at.For the clamshell opening action you first have to figure out how to get that motion to the rotor. Are you going to mount a motor in the rotor with sliprings feeding it, or are you going to use a mechanical linkage, e.g. via a thrust bearing that pushes on a concentric collar to operate the clamshells? If the former, a DC gearmotor with series limit switches bypassed by reversing diodes is vastly preferable, as you wont have to get a reliable control signal through the sliprings. Simply use a H-bridge to apply DC of one polarity to open and the opposite to close. Due to the limit switches, the motor stops drawing any power when its fully open or fully closed, though for both this and the rotation motor its advisable to cut power after a timeout so it doesn't burnout if something is jamming it.N.B. Internally, most cheaper servos are just a DC motor, a reduction gearbox, a position sensor (usually a pot) on the output shaft, and a little electronic control board. Rip out the electronics, and remove any stops that prevent 360° rotation, and you've got a very compact gearmotor.

author: Youkai
author_rank: Regular Contributor
timestamp: January 24, 2024, 08:26:06 pm
content: I was thinking the design would look something like this.Green is the stationary shell.Blue is the rotating part. It is mounted to green via some bearings. The clam shell mechanism is attached to Blue. Blue has a gear on it's inner diameter that I'll print.Red is the motor which is mounted to Green. Output shaft has a gear on it that meshes with Blue's gear.Purple are posts attached to Green (i.e. stationary). They have lever switches mounted on them and act as end-of-travel indicators.Teal is a bar mounted to blue which will press the lever switches and tell me to stop running the motor.This was my initial design concept. If position sensors or whatever are better options for the position tracking I can use those instead. This thread is to figure out that and the motor combination.