Hi Everyone!
I am an enthusiastic photographer/videographer, and i'm setting out to make a timelapse-slider. I have some experience with arduino.
The slider needs to slide a 5d with a lens (all together about 3pounds). The idea is to set it up with a potentiometer, so the speed becomes variable. I expect to build it, using the following components:
Stepper motor
Stepper Motor - 125 oz.in (200 steps/rev) (90N.cm)
Stepper Motor Driver
EasyDriver Stepper Motor Driver V4
Microcontrollor
Arduino Pro Mini 328 - 5V/16MHz (I will probably need the "FTDI Basic Breakout - 3.3V" to upload the code) Alternatively I am considering just buying an
Arduino Uno R3, as this is just as cheap...?
Potentiometer
Some random potentiometer
I am a little confuset about the power supply (or supplies) as it needs to be transportable. I need at least 7V for the stepper motor, and 5 / 3.3V for the driver and arduino mini. Does anybody have any ideas regarding this matter?
Your motor: 125 oz/in means it can lift 125 ounces at 1 inch from the center of rotation (for example a 2 inch pulley). 125oz / 16oz/lb = 7.8lb means you have enough torque to lift a 7.8lb camera vertically with that 2" pulley.
The driver: the critical aspect to watch for is to make sure it has enough amperage to feed your motor. The EasyDriver can supply 750ma max. If your motor is rated over 750ma then you will not be running it with full torque. Also note that the EasyDriver is designed for bipolar stepper motors (not unipolar).
An Uno is a suitable controller for this. For the potentiometer you want a 10K potentiometer with a linear taper (vs audio taper).
Any battery over 6V is suitable for this; the stepper doesn't care what voltage you run it at, the EasyDriver requires 30V or less, and the Uno requires 20V or less. You just need to make sure the battery has a good amp-hour rating; your project will use less than 1 amp per hour, so, for example, a 2Ah (or 2000mah) battery will run it for 2 hours. Good choices would be either a 2S to 3S LiPo battery or a sealed lead acid battery -- whatever is convenient and whatever you have a charger for.
If you're looking for slider hardware I'd recommend Makerslide which is purchaseable at Inventables.com.
Technically this is true, the voltage regulator IC on the Uno has a maximum input voltage of 20 VDC. However, it drops the voltage input voltage to 5 VDC largely by converting excess electrical energy into heat energy, and the heat output is proportional to how much the voltage has to be decreased. Extra heat is rarely a desirable situation for electronics, so I'd really try to stay within the officially recommended input voltage range of 7 VDC to 12 VDC.
2 phase = bipolar, 4 phase = unipolar. The EasyDriver is for bipolar motors only. "2A/phase" is the peak power it will use but average power is slightly less. Moot point because it's clear that your motor and driver are not compatible anyway.
A 2S LiPo is (3.7V * 2) = 7.4V and a 3S LiPo is (3.7V * 3) 11.1V nominal. Either a 2S or 3S is acceptable (a higher voltage battery allows you to move the stepper at higher RPMs) but you need to look for the mah (milliamp hour) rating to know how long it will last.
I read, that it's possible run a unipolar stepper motor on a bipolar driver. You just "ignore" the center tabs, and connect the wires at the end of the coils to the driver, making it "bipolar".
If this is the case (and I hope that it is), is it then possible to combine a stepper motor and driver like the following (both major sparkfun sellers):
The Big Easy Driver:
Bi-polar Microstepping Driver
2A/Phase Max
Max Motor Drive Voltage: 35V
On-board 5V/3.3V Regulation
is this possible/feasible ?
and is it understood correctly, that this constellation (running at full 2 Amps) would give me 1 hour if powered by a 3S Lipo 11.1V 2000 mAh battery ? Is it likely that this will run at full 2 Amps, pushing a camera of 3kg at ground level? Hope you can help me, regarding this matter...
Yes, a six or eight wire stepper can be driven with either a bipolar or unipolar driver. As an aside, a five wire stepper can be driven unipolar only.
The Big Easy Driver is also a good driver. It again is based on the A4988 chip like the Pololu driver I linked earlier. You don't really require the onboard regulation that the Big Easy has (your Arduino can provide the 5V needed), but I suppose it's only a few dollars more anyway.
At full amperage your 125 oz/in stepper with a 2" pulley can lift 3.5Kg vertically (more practically you'll be using a ~1" pulley with 7kg of lift). Given those numbers I'd suggest you're getting pretty close to overkill on the power. Due to the fact that sliders more typically move side-to-side you'll find yourself cranking down the amperage (it's adjustable on the Big Easy) to a mere fraction of that 2A limit and will be able to run it for quite a long time. If you're doing long term videos and pausing the movement of the camera between shots then you can disable the driver and use almost no current at all.
Chagrin, how would this be possible without you - You're the man! thanks...
How is it possible to adjust the amperage? is this done with coding, or with a potentiometer of some sort? and completely disabling the driver, you mean like unmounting it, and connecting the motor directly to the arduino?
There's a very small pot on the Big Easy that is labeled "CUR ADJ". Guess what that does?
The Big Easy also has an "ENABLE" pin. If you send a high signal to the enable pin it shuts off the power to the motor (which is kinda logically screwy, but electronic engineers are optimistic, glass-half-full people and hate to call things "disable").
