Every year we get into a situation where we need to speed-control a motor in some prototyping system and I always say I’m going to build some simple control circuit. I have limited electronics knowledge (enough to be dangerous) and I have found a simple circuit called: “Square Wave Signal Generator with Pulse Width Modulation”. The circuit
These will cable right to the speed controller via the PWM port. I just got a cheap one and powered it via a 3S lipo and a UBEC that I had laying around, but some of the better ones have more power options.
For prototyping purposes, we took apart an old drill and refitting things. Basically, a battery connector goes in the butt, and two wires with some quick connect fittings come out the top. Then it’s just a matter of plugging it into a battery and the motor, and you have instant, easy to use speed control.
The Jaguar PWM input is not 15khz. The input PWM is defined in the Jaguar Datasheet, available from VexPro (it’s called servo style speed input).
3S Lipo is a Lithium Polymer battery popular with RC hobbyists. Use a Robot Battery instead. UBEC is a Universal Battery Eliminator Circuit, in other words, a 5v converter.
If you want to buy, like ILAMtitan said, you can find many options at any hobby shop (usually called a servo tester). If you want to support FIRST vendors, here are a few other options, with varying capabilities.
Sorry for not clarifying, I come from the RC world where these are standard terms. A 3S LiPo is a lithium polymer battery pack containing three cells in series. Each cell is 3.7V, so the whole thing outputs a nominal 11.1V. There are also other cell count varieties, and I’ve seen up to 11S which would be 40.7V.
A UBEC is really just a highly efficient voltage regulator. It takes a voltage input above 6V, and drops it down to 5V. So the 3S battery connects to the UBEC input, and the output is 5V. This 5V is the standard TTL value used in servos and motor control systems. I used this one becouse it’s cheap and I didn’t need much current: http://hobbyking.com/hobbyking/store/__15212__HobbyKing_Micro_UBEC_3A_5v.html
I actually don’t recommend the LiPos if you aren’t familiar with them. They require highly specialized chargers and can be very dangerous is mistreated. A better battery option would probably be a cheep 4x AA holder. This would give you enough voltage to power the UBEC and feed into the tester and subsequently your servo or motor controller.
This is of course the low cost cobbled together way to do this. If you can spend a bit more, the two AndyMark products that Joe Ross linked will be much easier to us, and likely provide more features.
Thanks everyone for all the information. I managed to find an inexpensive servo tester on ebay that will ship and arrive quickly. I would have preferred to find something that I could have bought or built from local sources so I could have it immediately - but the closest reliable source for RC stuff is about an hour drive.
While I’m waiting for that to arrive - I’ll tackle the 5V power situation. Ideally, I’d like to create something that uses the same 12V robot battery that we will be using to power the motor on the other side of the jag, or some old power supply I have sitting around from an old laptop or something. I think my “enough to be dangerous” electronics can handle getting 5V out of something we have available.
While they nominally output 11.1V, they are charged up to 12.6V, or 4.2V per cell, and then drop down to around 9V at a minimum or else you probably damaged the battery. So really a robot battery will be a very similar replacement.
Just that the robot battery wont catch fire if you drop it the wrong way. Those LiPos pack quite a punch.
I looked at that information before I posted and my head started to spin. It looked like the kind of thing I would spend two days working on and have nothing happen as a result!
We have no one on our team with any expertise in arduino use. Learning this is on my to do list - but there’s a bunch of stuff higher on the list…I needed a more immediate solution. I may take you up on that AFTER the build season.