Hey FRC!
My team is going to build a new testing rig for electrical and we were wondering what kind of setup other teams used. Please give suggestions and improvements if you can.
Thanks!
Electrical testing rig…
Please be more specific. Otherwise, you’ll get a variety of responses involving some combination of a multimeter, oscilliscope, Battery Beak, West Mountain CBA, and possibly “a bunch of resistors, maybe?”.
Are you aiming to test electrical components? Systems? Or people who are putting the robot electrical system together? Do you have a particular price point (how much are you willing to spend)? Is there anything specifically you’re trying to look for?
We just had a control system and a few Talon SRXs on it on a large wooden board. Velcro kept everything down, so we could move the stuff elsewhere if we wanted to.
In just a few days my team threw together a bare bones control system on a sheet of wood with a roborio, VRM, a PDP, main breaker, and a battery with a few talons on it and you’ve got yourself a great testbench (that you can also use for training if managed properly) for prototypes, sensors, LED’s, and finished mechanisms! I’d also recommend adding on a basic pneumatics setup so that your pneumatic actuations can be tested easily, though by no means am I a pneumatics expert so I will leave the advice on how to do this to someone smarter than I am.
Hope this helps,
-Marcus
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I mean that’s pretty vague… it really depends on what you want to test. The Velcro and plywood solution works pretty well for testing individual components. Something more complex for testing motors and pneumatics since you’ll want to be able to prevent the motors and cylinders from moving unintentionally (rotational inertia is a thing). If you want to check PWM and CAN bus then you’ll want an oscilloscope…
Basically I’d recommend getting a good multimeter and a battery tester of some sort. Then get some plywood and Velcro and stick stuff on. Make sure you have some sort of quick connect crimps on your wires. That should be a good start for now.
If you are talking about a setup to just test motors, we used 2 talon sr’s. We controlled the speed of the motos by using an arduino signal to generate a pwm signal for them, and a potentiometer to manually adjust the speed.
We then put both talon’s and the arduino in a 3d printed box (aprox 4in by 4in by 3.25in) , with the potentiometer, a switch to control if the motors spin “forwards” or “backwards”, and another switch to toggle the controllers on or off. We then put two anderson powerpoles on one side (to plug two motors into), and one anderson power pole on the other side for battery input to power the talon’s and arduino. Having a small box to easily carry around (we feel) is a lot easier than carrying around a wooden board with motor controllers velcroed on like some teams have.
I don’t have any pictures of the box, but here are some cad pictures:
Box: http://i.imgur.com/NwH9WnG.jpg (note the powerpoles don’t hang out like that in real life, they actually have grommets to sit flush against)
Inside View: http://i.imgur.com/HgPhrZd.png
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*If you’re on a tight budget you can buy a serviceable pot-controlled PWM signal generator for $1.24 (including free shipping). You can buy a 12VDC-to-5VDC buck converter for 74 cents (including free shipping) so you can use the 12V FRC battery to power it.
I assume that you’re asking about an FRC electrical testing rig because that’s an important thing for any and every FRC team to have. Whether it is just a piece of plywood with components screwed on or as much as a chassis with necessary CS components.
If you can manage it, the chassis one is great because you can train new programmers on it for simple things. And for more advanced people, hook up sensors and cameras and the like to develop skills like PID and vision tracking. But if that’s not something you can manage that’s ok. A simple piece of plywood with things mounted on it is handy too. You can still learn how to use and test sensors but it may seem less applicable/interesting to people who are still yet to develop an interest. This is why I train my new members on a chassis. But to the sufficiently enthusiastic FIRSTer a test bed can be just as fun.
Giving it a compressor and some solenoids and cylinders can make for a great way to teach new members how to use them. (Credit to marcusbernstein for that idea. It didn’t occur to me that pneumatics would go on a test bed but that’s a great idea!)
You can follow these steps if you don’t know how to wire the board.
The FRC Pneumatics Manual and section 8.9 of the FIRST STEAMworks manual are the best resources for pneumatics.
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Don’t really know what kind of testing rig you are thinking about but we have several rigs that we built throughout the years.
- For testing motors, encoders and servos, we built a testing rig by using those obsolete LEGO Mindstorms and the old HiTechnic DC motor controller/servo controller (we have a FTC team and quite a few of those obsolete units).
- A few years back, we bought a “Motor Meter” from Andy Mark (http://www.andymark.com/product-p/am-2671.htm), attached a Talon SR motor controller to it so that we can use the “knob” to control the motor speed for testing the prototypes. We also modified the Motor Meter to add a three-way switch (Fwd-Off-Rev) so we can change the motor direction and changed the Motor Meter firmware to support this switch and the new behavior of the knob.
- Last but not least, we have built a simple switch-box that has a three way switch (Fwd-Off-Rev) that directly connects a motor to a battery so that you can drive a motor without any fuzz (i.e. no speed control, just on or off in fwd or rev direction). Actually, there are two switches so can control up to two motors simultaneously but one switch is a momentary switch and the other one locks (i.e. the momentary switch will go back to “off” when you let go).
- As if we don’t have enough summer projects, we are also considering building our own Arduino version of the Motor Meter because the Andy Mark Motor Meter had died over a year ago and we want more features than the Motor Meter can offer.
- A few years back, we also built a complete control system using RoboRIO. We called it “robot-in-a-box” and its companion “pneumatics-in-box”. Together, they can control any robot of any season. We use it to help prototyping each year when the complete robot isn’t done yet but we need to control a subsystem prototype or help software development without the completed robot.
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Care to share where and how to get prices like that? You’ve peaked my interest. :]
I was wondering if someone would ask:)
Go to eBay and type “servo tester” in the search box. Then sort by “price+shipping: lowest first”.
If you can’t find it that way, try typing “172688321485” in the search box. It’s presently on sale for $0.99 (with free shipping).
Here’s a picture of one of the several I purchased earlier this year and have been using, showing how to wire the power and signal cables. I glued it to a piece of cardboard to make it easier to tape it down to my workbench.
Did you want info on the DC-DC converters too?
Thanks for the information–I think I found the DC-DC converters using the same method you described for the servo tester. I’m typically wary about buying very low-priced components on sites like Ebay, but maybe I need to start having a little more faith in people. 
I purchased about six of those servo testers, one at a time, from six different sellers, over a period of a month or so earlier this year. I received every one of them by the promised date, and all of them work fine.
I also bought about a dozen or so different models of DC-DC buck converters (both linear and switching) and tested all of them. Here’s a sample.
One of the converters was DOA. I contacted the seller and he sent a replacement, free of charge, without requiring the return of the defective one.
So, for teams on a tight budget, this seems to be a low-risk solution that works.
On the right is the $1.24 (on sale for $0.99) servo tester (PWM generator).
On the left is a different model that I cut open to see what was inside.
In the center is a nice little 12VDC-to-5VDC buck converter that puts out more than enough current to drive the servo tester.
https://www.chiefdelphi.com/media/papers/download/4967
A word of caution:
I put a drop of superglue on the microswitch (under the plastic case) to immobilize it, and drew a black X on the case.
I always check to make sure the pot is roughly in the neutral position (center of travel) before powering up.