I have a small dc brushed motor and geartrain i would like to run an arduino to control. The geartrain actually compresses a spring and releases the spring in one complete cycle. Originally there is little mechanical cut-off lever, but i would like to nix that.
Ultimatly I need to get the motor to spin-up with a soft-start, run on full power until the load is released, then run again at half-speed or so until a slight load is detected at the begining at the next cycle where the motor will stop and the cycle is complete (ergo, "indexing").
For the speedcontrol I plan on using the uno or nano board to control an inverter-grade mosfet that will handle the load of the motor.
Is there a good resource to point out that shows the pros/cons of using a voltage divider, shunt, or H-bridge to monitor motor load/current?
Why don't you just get a Motor shield and use the ADAFRUIT MOTOR LIBRARY ? their not expensive and you can do anything you want with it including run servo motors. I'm not even a programmer and I was running my 6V dc brushed motor ramping up and down like nobody's business.
revetps:
Is there a good resource to point out that shows the pros/cons of using a voltage divider, shunt, or H-bridge to monitor motor load/current?
Of these 3 only a shunt measures current. Normally a shunt is a very low resistance (0.05 ohms?) so the voltage developed across it is much too small to be measured by an Arduino. It will need to be amplified. There is a discussion about it in this Thread Amplifying a small voltage - Project Guidance - Arduino Forum.
I suspect you are taking on a rather complex project.
The motor draws something around 15amps cont. @ 12vdc, more than most sheilds i've seen. I'm thinking along the lines to control the motor as a dc servo. Many industrial DC servos even if they are equiped with an encoder do not use the encoder to determine servo load in any way.
I'm tempted to program this as a macro, we'll see later though.
MarkT:
revetps:
For the speedcontrol I plan on using the uno or nano board to control an inverter-grade mosfet that will handle the load of the motor.
"Inverter grade" - meaningless marketing speak.
Which MOSFET? What voltage are you powering the motor? Is the MOSFET logic
level and does it have a low enough Rds(on) ?
looks like an RDS(on) of 0.0035ohms ------(VGS = 10V, ID = 121A ?)
I plan on running the motor with up to a 16vdc source, normally no more than 12v though, and yes, the fet is run at a logic level.
sooo, thoughts on determining servo load, without encoder feedback?
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So, in theory I could compare VDC of input to VDC on the motor/load side, by using a shunt and amplifying the signal, or a transistor of sorts. There is no shield or IC for this?
BTW if you see a TO220 MOSFET being quoted as taking 202A then you are being
lied to. 200A will rapidly fuse the leads of the package. Footnote (6) in the datasheet reveals
that the actual package limitation is 75A and the 202A figure is "calculated".... Even
the 75A figure is pushing it.
Pardon my most likely untrained eyes, but I don't see a huge difference between the IRF1404 and the BUK954R8-60E aside from a higher voltage and amp rating. Both Fets' are considered "logic level" on digikey and alot of guys have been using the IRF1404 for PWM controllers. I will through some BUK954R8-60E's on my next order since I like the higher ratings anyways.
The INRUSH current on motor startup (which you are calling "current spikes" can be reduced using an RC snubber , which is a resistor (with the correct power rating) and a capacitor (rated for the correct voltage) in series. When the motor starts up, the capacitor charges, (basically "absorbing" the spike) and the resistor limits the current . This is a standard practice. It is not uncommon to see these snubbers soldered directly onto the leads of small dc motors. Larger motors also have them but they are
physically located elsewhere. I do not have any experience calculating the values (power rating and value for the resistor , voltage rating for the cap) but I know they are used to reduce or limit the inrush current on motors.
Pardon my most likely untrained eyes, but I don't see a huge difference between the IRF1404 and the BUK954R8-60E aside from a higher voltage and amp rating. Both Fets' are considered "logic level" on digikey and alot of guys have been using the IRF1404 for PWM controllers. I will through some BUK954R8-60E's on my next order since I like the higher ratings anyways.
Note: 5V Arduino outputs may only have 4.1V when at logic HIGH.
IRF1404Z: From the datasheet, look at fig 1, pg 4 ... there's not enough voltage to sufficiently turn it on for your application.
IRF1404S, IRF1404L: From the datasheet, on pg 3 ... the lowest VGS they show is 4.5V ... it might work.
BUK954R8-60E: From the datasheet, look at fig 11, pg 7 ... this is completely turned on even at 2.6V. At 15 Amps continuous and 0.005 Ohm, it will dissipate 1.125 Watts.
When I look at the Transfer Characteristics curve for the IRF1404 which someone is calling a Logic Lever Mosfet I see that for a Vgate-source of 5Vdc I am only going to get 10A collector current. With the RFP30N06LE, I am going to get 50A with the same drive voltage. Doesn't that make a difference ? I don't know anything about MOSFETs but it sounds to me that if I use the RFP30N06LE, I don't have to because unless I need more than 50A, I'm going to be fine. If I am reading the graph correctly, I would need 5.5Vdc to get 50A with the IRF1404. That's only half a volt, but if you only have a 5V supply, if might as well be 100V. Am I
wrong here ?
raschemmel, I think you meant 30A for the RFP30N06LE. With everything being within spec, the main thing to consider is heat dissipation due to the load current and RDS (on). This will determine if a heat sink is needed. For example, when you're switching 30A, this transistor will dissipate 30x30x0.047 = 42.3W. Then say you switched this for another MOSFET with RDS = 4.7 mOhm, then now the heat dissipation would be 4.23W. For 10A current, the calculations are 4.7W and 0.47W.