Is it possible to ..........?

Projects General Guidance
1

Hi,

For my project, I need a motor that
1, Rotates in one direction only
2, Max RPM is about 30
3, Each rotation is at a varying rate (ie slow, ramping up to fast and then back down again)
4, The total RPM is controlled by radio control.

I can do it using a stepper motor, however, a nema 17 (12 volt) is not powerful enough, and a nema 24 will be way to heavy.

Is it possible to use my UNO and program a 12v DC motor, (with a gear head to get down to the correct RPM), so as to have the required varying rate.

I'm hoping that some-one can point me in the right direction

Mick

2

Hi Mick

I'm no expert on motors but I know you can drive a DC motor using a PWM signal from the Uno. You will need a driver circuit of some kind, possibly using a logic-level MOSFET. Tell us more about the motor you want to use; voltage, current etc.

You say radio controlled; explain exactly what you have in mind. An RC model car/plane type controller?
Paul

3

You can get some geared DC motors with very low gearing. Look for example at the Pololu website.

You could also gear down a stepper motor if you need more torque.

I have built some radio controllers for model trains using nRF24L01+ 2.4GHz transceivers.

I got my nRF24s working with this Tutorial

I suggest you use the TMRh20 version of the RF24 library - it solves some problems from the ManiacBug version

The pair of programs in this link were abstracted from the train control system and may be useful.

...R

4

Can you define total RPM ?

5

MickyK:
I can do it using a stepper motor, however, a nema 17 (12 volt) is not powerful enough, and a nema 24 will be way to heavy.

I think you are listening to the wrong people about steppers/reading the wrong web pages.
you are probably getting your mis-understandings from hobby forums (like this) that discuss toy steppers and mismatches one-size-fits-all electronics.

VERY loosly put, a stepper power is the ratio between stepper rated voltage and power supply voltage.

if you buy a 12 volt stepper and feed it 12 volts, you get "X" power.
if you feed it 24 volts, it will deliver about twice the power.

if you get a 3 volt motor and feed i 12 volts, it will have 4 times the rated voltage and deliver about 4 times the power.
feed it 24 volts and you get about 8 times the power.

this is all VERY loose with the rest of the calculations.

next you have stacks. a single stack motor will be about a cube, maybe a bit longer for the bearing housing, but the body between the end housings will be pretty thin. a double stack will have a body housing that is about 1.7 and a triple stack will have a body that is about twice as long as it is square.

on the high end of NEMA-17 motor is about 92oz in (torque)

compare to Poulu motor at about 51 oz-in.

as a forum note 'not powerful enough' is not something we can engineer with.
Are you using hobby parts like the A4988 driver ?
as a note, your speed is great for a stepper, they deliver better at slow speeds as they are constant torque.
as another note, your best power from a stepper will be when you drive it with about 30:1 volts ratio to nameplate.
that means for your 12volt motor, about 240 volts (impossible BTW)
or a 1volt motor at about 30 volts.

a final note is that when you delver that much power to a small package, you get the added benefit that you can cook eggs and chicken on it. it should not boil water, but you would not be able to keep your hand on it for more than a few seconds.

6

dave-in-nj:
I think you are listening to the wrong people about steppers/reading the wrong web pages.
you are probably getting your mis-understandings from hobby forums (like this) that discuss toy steppers and mismatches one-size-fits-all electronics.

Q "is it possible...?"

A "short answer: no. Long answer: yes." :smiley: :smiley: :smiley:

7

curious48:
Q "is it possible...?"

A "short answer: no. Long answer: yes." :smiley: :smiley: :smiley:

medium answer :

Anything that the mind of man..
...can conceive...
...and believe...
....it can achieve.

short answer is YES !

8

curious48:
Q "is it possible...?"

A "short answer: no. Long answer: yes." :smiley: :smiley: :smiley:

had to read that 5 times.....

NO has 2 letters. shorter than the answer that has 50% more letters. sigh.....

9

MickyK:
Hi,

For my project, I need a motor that
1, Rotates in one direction only
2, Max RPM is about 30
3, Each rotation is at a varying rate (ie slow, ramping up to fast and then back down again)
4, The total RPM is controlled by radio control.

I can do it using a stepper motor, however, a nema 17 (12 volt) is not powerful enough, and a nema 24 will be way to heavy.

Is it possible to use my UNO and program a 12v DC motor, (with a gear head to get down to the correct RPM), so as to have the required varying rate.

I'm hoping that some-one can point me in the right direction

Mick

Is it important to you to have spesific control over the RPM, so you can control the motor to run at an exact speed? Or do you just need to roughly speed up and down between standstill and top-speed?

10

dave-in-nj:
medium answer :

Anything that the mind of man..
...can conceive...
...and believe...
....it can achieve.

short answer is YES !

What if I wanted to travel to the center of the galaxy tomorrow, and pet the small purple turtle that lives there?

11

Thank you Gentlemen,

Paul,
I can drive a simple 12v motor, controlled remotely by a 2.4 Gig radio system, at varying rpms, via PWM.
The whole project is a RC controlled rowing boat.The motor can run on 14.4 v NiMh batteries, the Uno on 9v.

Robin,
there are heaps of gearhead motors on the market, but what I have found by looking at the specs of individual motors is that the start-up amperage can be up to 10 amps. This would turn my battery pack inside out, suck it dry, and spit out the remains in a cloud of smoke!

Dave,
My Nema 17 is the top end (90.2 oz\in). When it is running loaded, it skips steps, NOT a good sign!
It's taken about 2 years to get to this stage, I don't intend giving up just because some stupid motor won't do what I want it to do!

Rupert,
Within each revolution, the motor runs slowly, ramping up to fast, then back to slowly. Finally, the ramping rate will be decided largely by trial and error, and what is possible.
It has to revolve 30 (max) times a minute.
Overall, the RC controls the 30 RPM stage.

I have looked at dc gearhead motors with encoders on the motor shaft, but these gearhead reductions are quoted to be 40:1, 500:1, etc, in reality they are 40.? ? ? ??:1, 500.? ? ? ?:1, They do this to reduce the wear on the teeth in the gearbox. It also means that if you tell the motor to do (say) 500 revolutions, the out-put shaft will do 1.? ? ? ? revolutions. Over a period of time, the out-put shaft, and therefore the whole mechanism will be out of sync, and the mechanism, the way it has to be designed, will have a massive heart attack.
I know, been there, done that.

That is the state of play at the moment, I will continue to research motors, encoder systems, programming issues etc,

Any pointers would be greatly appreciated.

Mick

ps: aarg, Ford Prefect hitchhiked, can you bring back a GargleBlaster for me please.

12

dave-in-nj:
had to read that 5 times.....

NO has 2 letters. shorter than the answer that has 50% more letters. sigh.....

okay, that's not what I meant. I meant that the reason the short answer is "no" is because it's not very easy, you can't "just do it". But if you take the time to really, really, really research it, then actually you can.
Take my project - I'd like to make like a million or ten million < $5 raspberry-pi like devices, + like $1.20 to put a complete arduino subsystem on them (so that they're two subsystems), have the arduino side be able to be programmed from the raspberry pi-like side; have the arduino be able to turn off and turn on the raspberry pi-like side; have tiny power consumption and work for a year on a few AA batteries, have the same price and size and connectors and abilities (or as close as possible). etc etc.
So, a lot of people think the raspberry pi zero is like a marketing stunt. So the short answer to whether I can do it is NO!!!! But maybe the very long answer is actually...yes :slight_smile: :slight_smile:
this seems to be the case with what the OP is asking in this thread, which I say because someone mentioned that the stepper motors discussed in hobbyist forums (like most of arduino) aren't good enough, but that these things exist. . . So maybe in his case (too?) the short answer is No, but the long answer is...Yes.

13

MickyK:
there are heaps of gearhead motors on the market, but what I have found by looking at the specs of individual motors is that the start-up amperage can be up to 10 amps. This would turn my battery pack inside out, suck it dry, and spit out the remains in a cloud of smoke!

What batteries are you using?

Most re-chargeable batteries that have enough capacity for steady running for (say) 20 minutes or more would have no problem with the brief start-up demand.

...R

14

I see. So the varying speed is to simulate the movement of the oars. Slowly through the water and quickly through the air. That's why the RPM varies through a single revolution. The remote governs the overall average RPM.

In that case there is a problem using a DC motor. Unlike a stepper motor, it's not easy to know when a revolution has been completed. You can time it, but it will quickly get out of sync. You need some kind of sensor to tell the Arduino a revolution has been completed. For example a microswitch that gets activated by the oar mechanism at the top of each revolution.

To drive the DC motor, I suggest a MOSFET such as stp16nf06l. Connect the MOSFET's gate to an Arduino pwm output with a ~330R and put a 10K pulldown on the pwn pin. Drain goes to ground and source to the motor terminal, the other motor terminal to 12V. You will need a high voltage suppression cap across the motor terminals eg. 0.1uF. A flyback diode will also be needed across the motor terminals, e.g. in4001.

As I said, I'm not a motor expert so someone please confirm my advice is correct.

15

Sorry. I did not read the whole of Reply #10 so I did not see it was a rowing boat.

What about using a regular servo to move the oars back and forth and a separate servo to lift them up and down.

Servos are very easy to use with an Arduino and they are also easy to fit.

...R

16

MickyK:
Dave,
My Nema 17 is the top end (90.2 oz\in). When it is running loaded, it skips steps, NOT a good sign!
It's taken about 2 years to get to this stage, I don't intend giving up just because some stupid motor won't do what I want it to do!

ps: aarg, Ford Prefect hitchhiked, can you bring back a GargleBlaster for me please.

I would not recommend a stepper be run on battery power. they are so damn power hungry.

if you are missing steps, then your motor is too small. The power supply is too weak, or the driver is not ramping properly.

Arduino's are not known for their perfect stepper timing. like rowing, you have to apply power at the exact time. apply power too early and you're going to get an oar in the back. too late and the guy in front of you will. ramp speed and motor voltage are tied together. how fast you can dump power into the motor has a great deal to do with your driver and also voltage.

as for the GargleBlaster.... not for me, last time I had one, they pulled me off the bar whilst I was singing shanties.