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Help choosing motor and parts for project
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Help choosing motor and parts for project

by mpol on Mon May 03, 2021 2:31 pm

Hi guys -

I am trying to build something similar (without the drill ofc) to rock a baby rocker similar to this in function:
https://www.youtube.com/watch?v=MMVUSgC3ULk

I want to use a Raspberry Pi and shield here:
https://www.adafruit.com/product/3775
Hat is either this (best for stronger motors):
https://www.adafruit.com/product/2348
Or this (best for overall projects, but only supports 5v for motors):
https://www.adafruit.com/product/3957

First question: Do I need a more powerful motor to rock a baby rocker than 5v?

Second question:
Can someone please help with recommending an appropriate motor?
Some ideas I had were here:
https://www.adafruit.com/product/3802 <-- Would this even be powerful enough?
https://www.amazon.com/Roeam-Bearing-3500-9000RPM-Versitile-Electric/dp/B07R5XFLZT <-- Or this (I like this because it has more power, but is it overkill or would it even work with the hat?)

Very open to the type of motor to use, with little experience I am worried I will get something either incompatible or not strong enough (or too strong).

Third question:
I would need a power source to power the motors. I found these but which one would be best for this project? Again open to others if these are not right..
Power options:
https://www.adafruit.com/product/352
https://www.adafruit.com/product/276
or something else?


Thank you so much for your help, really excited to start the project and first time posting in the adafruit forums :)

mpol
 
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Re: Help choosing motor and parts for project

by adafruit_support_bill on Mon May 03, 2021 3:00 pm

The first step is to choose the motor, Once you have selected a motor, you can look for a driver capable of running it.
https://learn.adafruit.com/adafruit-mot ... tion-guide

For that type of application, you want a motor with fairly slow rotation, but high torque. The Amazon motor at 9000 RPM is way too fast. A gear-motor like the 90:1 TT motor is a big step in the right direction. But I suspect that you will need something with a bit more torque. One of Pololu's gearmotors would probably be a good choice. The 150:1 models have a no-load rotation speed of 67 RPM. Under load, you would probably see something closer to 60 PRM or 1 rock per second. the 12v model would work fine. The 24v version will run cooler for the same power output.

The DRV8871 would be a good choice for a motor driver. It can handle up to 45V and 3.6A. Since you don't need to reverse direction, you just need one GPIO pin to control the speed via PWM.

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Re: Help choosing motor and parts for project

by mpol on Mon May 03, 2021 4:36 pm

Thank you for your help and reply Bill. I'm really new to this so I will have more questions as I go along.

The first step is to choose the motor

So great point on "rocks per minute" - I think I would want a max of 2 rocks per second, with the ability to slow it down to 1 rocks per second. So variable speed of 2 rocks per second - ~1 rocks per second.

Again I'm new so it's hard to read or search for the right motor specs. I found this product page for motors:
https://www.pololu.com/product/4754

Question #1: Which voltage is recommended? They have 12v and 24v. At least with the 12v it would work with https://www.adafruit.com/product/2348

And since I wanted to get 2 rocks per second max I was thinking of an RPM of 150-200....
Question #2: thus would either this: https://www.pololu.com/product/4744 or this: https://www.pololu.com/product/4684 do? (I assume with either I could speed these up to either ~2 rocks per second or ~1 rocks per second? Please let me know if not..)

The DRV8871 would be a good choice for a motor driver. It can handle up to 45V and 3.6A.

Is this the same as this? https://www.adafruit.com/product/3190? It says it's "Out of stock", would you know when this would be available again? Anytime soon? :)

I really like the DRV8871 motor driver because it's perfect for the motor type I want; it supports up to 3.6a (the other hat I linked before, the DC & Stepper Motor HAT for Raspberry Pi only supports up to 3a). Would the DRV8871 or the Hat I linked be equally easy to code for?

Thank you so much I can't say it enough :)

mpol
 
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Re: Help choosing motor and parts for project

by adafruit_support_bill on Mon May 03, 2021 4:51 pm

Again I'm new so it's hard to read or search for the right motor specs. I found this product page for motors:
https://www.pololu.com/product/4754

Question #1: Which voltage is recommended? They have 12v and 24v. At least with the 12v it would work with https://www.adafruit.com/product/2348

No. It would not work with that. The stall current for that motor is 5.5A. Which would probably mean the maximum efficiency would be somewhere around the 3-4A range. Well above the capability of the motor HAT. The DRV8871 is a much better choice for a driver. And could handle either 12v or 24v.

Is this the same as this? https://www.adafruit.com/product/3190? It says it's "Out of stock", would you know when this would be available again? Anytime soon? :)

We should have them again fairly soon. If you sign up for notifications, you will get an email as soon as they are back in stock.

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Re: Help choosing motor and parts for project

by mpol on Mon May 03, 2021 6:22 pm

Okay thank you.

Will the Adafruit DRV8871 DC Motor Driver Breakout Board - 3.6A Max (https://www.adafruit.com/product/3190) board work easily (hence keyword is easily) with the Raspberry Pi 3 B+, or for easy should I get an Arduino compatible board? I have an Arduino board in storage but don't have a Raspberry Pi 3B+ board which is why I really want to use a Pi board.

mpol
 
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Re: Help choosing motor and parts for project

by adafruit_support_bill on Mon May 03, 2021 6:36 pm

Either a Pi or an Arduino are more than capable of controlling the DRV8871.

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Re: Help choosing motor and parts for project

by mpol on Wed May 05, 2021 2:06 am

Thanks again Bill.

Lastly in buying supplies I need power supplies for both the Raspberry Pi 3B+ and the DRV8871 motor board.

What should I look for in each power supply? I know I need 5.xV for the PiB+, what about amps is 1A enough like here?
https://www.adafruit.com/product/501

Same question for the DRV8871 motor board, I want to buy something universal I could reuse for other purposes so I was looking at this one here:
https://amazon.com/Adjustable-Adapter-Switching-100-240V-3-3-24-7V/dp/B07T2SFGHN

I'm very open to other power supply recommendations as well, so please recommend others if you have them!!! Again thank you for helping me make this a reality!

mpol
 
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Re: Help choosing motor and parts for project

by adafruit_support_bill on Wed May 05, 2021 6:26 am

The Raspberry Pi official site lists power supply recommendations for their boards. For the B+ they suggest at least 1.8A:
https://www.raspberrypi.org/documentati ... /README.md

We have a 5v@2A supply that should work: https://www.adafruit.com/product/1994

The Amazon supply should work for the 24v Pololu motor. It would be marginal for the 12v. (At 12v you need twice as much current for the same power)

A good 12v option would be: https://www.adafruit.com/product/352

I want to buy something universal I could reuse for other purposes so I was looking at this one here:

Adjustable supplies can be a double-edged sword for some kinds of projects. Motors can tolerate a wide range of supply voltage variation, but many electronic circuits are easily destroyed by a volt or two over the limit.

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Re: Help choosing motor and parts for project

by mpol on Thu May 13, 2021 3:55 pm

Hi Bill -

Thanks again for all your help. The parts are starting to trickle in from the different stores.

I had a question on how to determine the appropriate wire gauge for the motor. I have these wires I am using on my breadboard: https://www.amazon.com/gp/product/B01EV70C78

But I need to run wires from the Pololu 12v motor: https://www.pololu.com/product/4744 to this 12v power supply: https://www.amazon.com/gp/product/B01461MOGQ. What wire gauge would you recommend (can I use the same wires I use for my breadboard? I'm thinking not as they are too "small"/"narrow").

Also I have to connect wires from the Pololu 12v motor to the DRV8871 motor driver board. Can I use my breadboard wires here or should I use a different gauge wire?

And lastly from the DRV8871 motor board to the Raspberry Pi Pico I'm using. Assuming here I can run the breadboard wires as well?

Thank you so much as always, your help is much appreciated and making it so I can complete this project.

mpol
 
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Re: Help choosing motor and parts for project

by adafruit_support_bill on Thu May 13, 2021 4:09 pm

Amazon doesn't have a spec for the wire gauge on that. But typical gauge for ribbon cable is 26AWG. That is marginal, but functional for very short runs. If you need to go more than a few inches, I'd size up to 22AWG or larger. 18AWG speaker wire readily available and would work well for your project.

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Re: Help choosing motor and parts for project

by mpol on Thu May 13, 2021 5:10 pm

Thank you Bill..

What about wires to/from the DRV8871 motor board and Pololu motor? And what about wires from the DRV8871 motor board to the Raspberry Pi Pico. Those can all use wires from the breadboard? Would any of those (maybe DRV8871 motor board to Pololu motor) require 22/18 AWG?

mpol
 
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Re: Help choosing motor and parts for project

by adafruit_support_bill on Thu May 13, 2021 6:28 pm

Signal wires between the Pico and the DRV8871 don't carry much current, so they can be as thin as you like. Power and ground wires from the power supply to the DRV8871 and from there to the motor should be more robust.

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Please be positive and constructive with your questions and comments.