I am building a device which will make use of 7 motors (all 12VDC). The specs (currents listed are stall currents)
3 @ ~5A each - bidirectional use required
2 @ ~2A each - bidirectional use required
2 @ ~2A each - bidirectional use NOT required (but would be nice if it were at little to no extra cost)
For a safety margin, I would be happiest to have a capacity of 1.5-2x that. I haven’t laid out the enclosure yet, so I don’t know if heat buildup might be an issue. Am I correct that keeping well within specification will result in less heat and a happier controller?
The motor controllers will be commanded by an Arduino Mega using NewSoftSerial library.
I have a Trex controller (DMC01) which I would like to use.
Which motor controllers should I purchase to supplement the Trex I already have? Do I need to bite the bullet on another DMC01 AND a DMC02 or is there a less expensive way?
Just to verify, are those currents the stall current at 12 V? Often, the stall currents will be specified at a rated voltage like 6 V, so I just want to make sure you’re properly accounting for the voltage you will be using in your project. Also, will your motors be generally be operating under heavy loads (i.e. near stall)?
Hrmmm…the motors for which I have specs just list “Stall current”.
The three 5A bidirectional motors will be operating under a fairly consistent load pushing lots of water - I don’t have specs per se, they are simply stamped “Protect with 5A fuse”, (which I will be doing) so I am assuming that they won’t reach stall.
The other motors are Cytron SPG30 series motors which simply lists stall current as 1.8A. I can’t post the datasheet itself (its 1.1MB) and I think its bad manners to post a link to a competitor’s site on your forum.
I appreciate your tact, but it’s fine to link to their datasheets here. Stall current varies linearly with motor voltage, so it doesn’t really mean anything to specify one without the other. Will your lower-power motors be operating much near stall (do you have any sense for how much current you will want to be able to deliver continuously)?
Thanks Ben, the datasheet is found at http://www.robotshop.com/content/PDF/specification-mo-spg-30-300k.pdf. It specifies 12V as the rated voltage.
Those motors shouldn’t be stressed much - I overspec’d the torque requirements by a fair margin and their duty cycle will be very light: probably no more than 30 seconds of use every 15 minutes. They will be be turning threaded rods.
The motors which will get the most stress are the 5A motors. They will operate quite frequently and have to push water.
As an additional question, does it make sense to protect BOTH sides of the motor controller with 5A fuses? ie between power source-motor controller and motor controller-motor?
The “Rated Voltage” at the top of the specs table basically applies to the rest of the specifications in that table, so it looks like the stall current you mentioned is indeed accurate for your 12 V system.
For your four 2A motors, I suggest you use two qik 2s9v1 motor controllers. Each qik is a serially-controlled dual motor driver that can deliver a continuous 1 A per channel (3 A max), which sounds like it will be plenty for your application. For the third 5A motor, your cheapest option would be to go with our lowest-power Simple Motor Controller 18v7. Note that you might have an easier time using three SMC 18v7s, one for each motor, rather than trying to simultaneously use a TReX and one SMC for your three motors.
The qiks and SMCs are newer controllers that can be chained together on the same serial bus and controlled using the same protocol. Unfortunately, the TReX is an older controller that uses a slightly different protocol. It should be possible to control them all from the same serial bus, but things will get a little more complicated (e.g. you will need to disable the TReX’s “shutdown on serial error” feature). Or perhaps you could control the TReX using a second, separate serial bus; you can look to see if two NewSoftSerial objects will play nicely together.
If the goal of the fuses is to prevent each motor from drawing more than 5 A, you should put the fuses between the motor and the motor controller, not between the motor controller and the power supply. For example, if you have your TReX controlling two motors and you want each to be able to draw up to 5 A, you would need a 10 A fuse between the power supply and the TReX, but then there’s nothing to prevent one motor from drawing the full 10 A while the other motor is drawing nothing. If instead your goal is to protect the controller because you have a really beefy motor, then you’d put the fuse between the motor controller and the power supply. Does that make sense?
Thanks for that. It was very helpful.
Just for some closure on this thread, I went ahead and purchased another Trex and a Trex Jr. I considered your advice carefully, but in the end, I based my decision on:
uniformity: keeping the code and hardware consistent was more important to me than I’d realized when I asked for advice.
greater utility for future projects: the Trex’s greater current capacity allows me to use larger, more powerful motors in future projects.
SMC config software: I don’t use Windows so the config utility of the simple controller was not the advantage it might have been otherwise.
I do appreciate your advice and willingness to recommend less expensive options.
Thanks for your explanation of your decision. By the way, the SMC configuration software also works on Linux.