Hi All,
I am looking into building a small robot for teaching programming. I want to use all tetrix parts and use the control systems from FRC. The problem is the battery from FRC is WAY to big. Could I use a smaller battery like the tetrix one and connect it to the PDP board?
The full robot would be:
4x Never Rest 40
1x Never Rest 20
RoboRio
PDP
VRM
Radio
Few Extra Sensors
5X Talon SRX
Thanks,
Tomy
The battery seems to have the same voltage, so it might be okay… Note however that its a 3Ah battery compared to the 18Ah batteries that FRC uses, so it will last nowhere near as long. Personally, I would recommend just biting the bullet and going with the normal battery, though. It will save you a number of headaches.
I think it will be alright, though it will not last very long since it is much small than an FRC one.
The problem is I will be using two never rest 40 motors from andy mark to drive the robot. So the extra weight will really kill the drive motors.
I’ve seen FTC robots driven on NeveRests that can go a reasonable speed. If all you want to do is play with syntax, the extra 13 lb aren’t much of an issue.
You’re on the right track with the electrical setup, though in the name of all that is good and holy use AndyMark Nubs or Actobotics hubs instead of the ones that come in the TETRIX kit. Set screws for torque transmission is bad.
4x NR40s on drive will handle an FRC battery as cargo just fine, assuming that you’re following good drivetrain practices and supporting the battery with a suitable bracket rather than just plopping it on top of the motor (though that will survive for a while). I’ve seen several TileRunners scooting around with them (and much much more) on top.
Also, stall current on a NR40 is 11.5 Amps. Unless you’re planning mecanum drive, you can splice the wires together and just run both NeveRests off of one Talon SRX per side (which is rated for 60A). Or if you want to experiment with follower mode, a Victor SPX would serve the purpose for less if you’re buying new motor controllers for the purpose. (If you already have that many SRXs around, well, play ball.)
Awesome thanks for the info about the nubs. I honestly didn’t know about them. I might have to redesign a little for the battery.
For the drive train I am using two tetrix max wheels in the center and 4 omnis on the outside. There is a rack and pinion lift as well as a simple pivot point arm. I wil be attaching this to each of the arms.
The goal of this robot is to quickly teach new students syntax, basic code, auto modes, tuning PID loops for different scenarios etc.
There is no reason you can’t use the FTC 12v battery. If all you want is a programming test bed it should be fine. It won’t last as long as an FRC battery but an FRC battery for just 5 neverrest motors is probably over kill.
That’s the conundrum. It’s only 5 neverrest motors but an FTC battery wont last to long and an FRC battery is overkill.
I don’t want to be teaching about PID loops and have to change the battery ever 30 minutes.
We built one of these as a programing testbed last year. It works well for our purposes and uses standard FRC parts, making it’s behavior more comparable to an FRC robot.
Granted this might not be the best fit for everyone, but I think it does a pretty good job. If you didn’t want to use CIM motors, you could probably swap out the gearboxes for the PicoBoxes used on the TileRunner.
Loving this thread - I am interested in doing something similar.
cbale2000, do you have any photos of how your peanut chassis looks when you’ve added a full control system and battery?
I’d try the single FTC battery and see how it does. If 1 doesn’t last as long as you desire then use 2 in parallel. Then you have the option of either putting the 2 fresh batteries in there or just 1 and “hot swap” in a fresh battery and then you don’t have to worry about shutting down and restarting everything.
AGM 12V batteries are available in a variety of capacities*. I have a 5Ah one and a 9Ah one which I use for some of the intermediate test robots I play around with. While it’s a bit of overkill, I have an SB50 charging port on the little robot with he 5Ah battery so I can use the same charger I use for a full-size battery. My advice is to figure out how much capacity you need for a charge to last through a full class period, and design with that.
Here is my almost FTC legal sized robot that is a full FRC robot. It uses two FTC flat batteries in parallel.
https://drive.google.com/file/d/15xQ1I8eb7upXSWKRQY3o7EZeTQdlQs3v/view?usp=sharing
The base is a Agent 390 https://www.servocity.com/agent390
The only thing I don’t like about it is that it has treads instead of a west coast drive. I was thinking of converting it this summer.
-Jim
Looks cool. I will post the cad model I have going so far of the one I’m designing tonight.
Are those the new RevRobotics batteries or the Tetrix ones?
Tomy
From the picture, those are definitely REV batteries. Still NiMH packs, with the pros (smaller and lighter than an FRC battery) and cons (different chemistry means different charger, maybe not enough capacity for really long runtimes) that come with it. 
We do something similar…
Pics/Source
GitHub - CrossTheRoadElec/deprecated-HERO-PixyDrive: Demo project using the HERO Control System and Pixy Camera. First shown at FRC Worlds Competition at CTRE booth.
Build of Materials
deprecated-HERO-PixyDrive/Robot BOM.csv at master · CrossTheRoadElec/deprecated-HERO-PixyDrive · GitHub
… probably would need to be larger to fit a RIO/Radio solution, this one is HERO/CAN based.
We use the TETRIX battery, got about half a day before needing to change it. Another benefit of smaller robots is that they generally draw less power.
Thats what I was thinking to. I’m going to design the FRC battery into the robot.
Tomy
I had planned to do something like this as a summer project. I’m trying to find a reasonably priced chassis/drivetrain kit (like a mini version of the FRC KoP kit chassis), so we can focus on programming rather than design and assembly. I’d hoped to spend no more than $400, but jeez this stuff is expensive, and it looks like that’s not feasible with what I’m finding. Some great suggestions above that I may still pursue, but any newer suggestions near that price range? (We have all the FRC control system parts, motor controllers, etc., just maybe not the motors that’d be best suited to a mini bot.)
Coming from an FTC member here. The neverest motors will be able to handle alot as long as they aren’t direct driven. The typical motors for a ~40 lbs bot is 4 20:1s, but 2 40:1s would work, so weight of the battery shouldn’t be an issue. Idk how heavy FRC electronics are, but it shouldn’t be that heavy. The one thing that might make testing for software work difficult is the Tetrix parts though, as they are hard to build reliable drive trains and mechanisms out of.
