Non-FRC Motor Controller?
 

Hi everyone,

I was looking for a couple of motor controllers for some personal projects of mine and was wondering if you all had any suggestions. It seems like everyone and their dog sells an arduino motor controller shield, and then there's also the stand-alone motor controllers.

I would use the controllers for FRC except those are expensive (victors are $90, jaguars $110) and seem (are they?) to be overkill.

If anyone has had success with a low-cost motor controller (either PWM or arduino shield preferably, though I2C could also work).

Also, do I need to get a speed controller, or can I just rapidly pulse on/off? I'm just a programmer, so I don't know if I'll burn out the motors or blow a fuse that way :D

Re: Non-FRC Motor Controller?
 

What motor are you planning to control?

Re: Non-FRC Motor Controller?
 

For small personal projects I have used this with success:
http://www.sparkfun.com/products/9571
Note that it can only supply up to 2Amps per motor or 4amps total.

The biggest questions is how many amps do you expect your motor to draw?
If it is as big as the FRC motors an victor maybe be your cheapest option.

Re: Non-FRC Motor Controller?
 

If your motors are DC brushless, not DC brush, there are quite a few cheaper options than the FRC electronic motor controllers, for example:

http://www.hobbypartz.com/skyrcesc.html

Re: Non-FRC Motor Controller?
 

OK, so I don't even know how much current I expect the motors to draw. Mainly because I don't know what motors to use, either :D. I know that motors are (generally) much cheaper though, so I figured if I screwed that one up I could just buy more :P

I'm figuring around 6V for the motor, probably 0.5-1A current draw, but what do I know? If any of you have any input on that, let me know. Unless it needs to be 12V (the internet doesn't seem to have many 6V motors) in that case I'd probably go with the small banebots motors or similar.

Re: Non-FRC Motor Controller?
 

I think RadioShack still sells small DC brush hobby motors and those motors with a realistic mechanical load can be controlled with the L298 (the integrated module on the SparkFun PCB linked in this topic).

Those motors are usually good to around 6V.
http://www.radioshack.com/product/in...ductId=2914699

They sell a 9V version but it's more speed than torque, maybe too much speed to gear it down without issues.

Re: Non-FRC Motor Controller?
 

Thanks all of you for your replies. Just so that I can get a bit of an understanding, do I need a full blown speed controller? Or can I just get a relay and pulse it at a high frequency? Forgive my inexperience with electrical work...

And just out of curiosity, most of the FRC size motors have a no-load current of about 1A. If there's only a small load on the motor, how much does this go up?

Lastly (and this will sound like a stupid question) if I got one motor controller, could I run multiple motors off of it as long as I don't exceed the rated amperage?

Re: Non-FRC Motor Controller?
 

A CIM on stall will draw 120+ Amps or more.

A typical 4 CIM robot drive often sits between 25A-45A per speed controller.

You can drive a motor in a single direction with MOSFET transistor(s) easy enough.

I would not attempt to pulse a relay. You'll eventually damage the contacts.

The Innovation FIRST Spike relays are really similar in design to the electronic motor controllers (they are also H-Bridge circuits), but are no match for the larger motors. I've not tried pulsing them but as they are solid state it might work.

Re: Non-FRC Motor Controller?
 

Well lets take the biggest motor in FIRST the CIM motor as an example. When the motor spins with no load it draws not a lot of current, 1-2 amps maybe. However when I put the motor in a robot and use that robot to push another 150lbs robot the load on the motor causes it to draw more amps to supply more power which is required for something like pushing another robot, P = V*I. The Victors/Breakers lets the motor get up to 40 amps before they get cut off.

Excuse me if there is any mistakes in my explanation, not an expert on the topic.

And in FIRST running multiple motors on one controller is not legal however doing this for other projects is okay if you do not exceed the amp rating, at least in my experience.

Re: Non-FRC Motor Controller?
 

The self-reseting breakers allow some massive spikes in current before they actually open. It's easy to draw upwards of 90A through them before they open.

Re: Non-FRC Motor Controller?
 

Oh yes, the 40amp number is continuous draw.

Re: Non-FRC Motor Controller?
 

Not disagreeing, but how do you know this? Did you find a schematic, or perhaps take one apart?

Re: Non-FRC Motor Controller?
 

http://www.robotmarketplace.com/prod...sersManual.pdf

"Spike is an H-Bridge relay module custom designed for Robotics applications. The most common use of Spike is to drive small motors in Forward, Reverse or Off. Spike can also be used to turn ON or OFF solenoids and lights. Spike takes input power from a 12V battery (labeled 12V, GND) and provides two outputs (labeled M+, M-). M+ and M- are typically connected to a motor. The unit is controlled via a three-wire interface, which connects to the Innovation First Robot Controller. Spike has a 20A integrated fuse to help protect the unit and it has an indicator to show status."

(That might have been my shortest post ever :D )

Re: Non-FRC Motor Controller?
 

Step 1 is to identify the current draw of the motors you want to control. Figure 3 to 6 Amps for small motors, smaller than what you'd see in FIRST.
Second decide on a voltage. Much of the world is 12 volts, because of the automotive industry. Most motor controllers you will find handle a wide range of voltages.
Then pick a motor controller that handles the current and voltage you want, has the control inputs you plan to use (e.g., PWM), and fits your budget.

Pulsing a relay, whether electromechanical or solid=state, is not a good practice.

The EM relay's contact will last only a few hours (they do wear), the maximum switching speed is single-digits per second (poor control resolution), and since you will have a hard time controlling the on-off time (duty cycle) the motor will be hard to control other than on and off.

Solid state doesn't have the contact wear, but the other issues remain valid.

The bottom line is, if you want to control a motor, use a motor controller.

You CAN build your own motor controller for under $20, but given your level of experience perhaps you should wait on that.

So, go find some motors....

Re: Non-FRC Motor Controller?
 

Where did you find this information? It's totally wrong.

Spike relay modules contain a pair of simple physical relays that use a pair of logic level signals to independently switch each relay's output between the 12 volt power and "ground" return inputs. When wired to motors, both relays are usually connected in an H-bridge configuration, but they don't have to be used that way. They are just as easily used as separate circuits, such as when powering LEDs or pneumatic solenoid valves.

Pulsing them is not recommended, as they are rated for a finite number of cycles and are likely to fail either electrically or mechanically.