Right now we have a CIM-U-LATOR gearbox hooked up to a modulox gearbox.
We want to get the speed of the overall output.
So, a few questions
Does the encoder fit on the CIM shaft?
If it does, then I assume we’ll need to put it on the CIM shaft and perform math in the code to find the speed after all the gearing within the gearbox?
It’s very high up on the robot, and the encoder wire seems short. Any suggestions?
Looking into some parts, I found
Are these the parts needed?
it looks like there’s a circular part of the hex shaft, and it is meant to protrude from the gearbox, and you attach the encoder there, while the hex protrusion on the other side is used as the normal provided hex shaft would be.
One is to connect it to the DSC; this option will require two Digital I/O channels because of the nature of the encoder output. If you take this route, make sure that you take care soldering the wires (there are alternatives to connect the wires; search the forums to find them) as they are easily damaged by the heat, and that you solder them correctly.
The other is to, as you note, connect it to the Jaguar via the encoder interface. Note that the E4P encoders provided by USDigital do not have index lines, so that pin is unused. Accessing encoder output through this option is only possible with Jaguars on CAN. Jaguars on PWM cannot react to encoder input nor send it back to the cRIO. You must be on CAN to access the encoder input. I’m not familiar with the specifics; I’ll let someone with more knowledge on that elaborate.
I’m not familiar with the specific parts you’re using, but yes, the cylindrical portion of the shaft is where the encoder reads the shaft’s rotational speed. If you still have FIRST Choice points left, you may also want to look into getting the encoders from there.
The US digital encoder is for a 1/4 shaft. The CIM-U-LATOR has a 8MM shaft. will not work. The MOD box adapter shaft will work. Just adjust the encoder counts by the gear ratio. Most of the AndyMark gear boxes has the encoder on the output shafts.
Encoders are sensitive to shaft end play & egocentricity. So make sure the shaft does not have a lot of float & is well aligned.
Splice longer wire to the provided encoder wire. Stranded Ethernet cable works. Cable is better than individual wires. Nothing bigger than 18 gauge. Try to keep the cable away from power wires especially motor power.
They may actually have a free speed RPM of 10000. But that would be only if the gear ratio really was the 2.7:1 in the cimulator followed by the 1:3 that he is talking about. I don’t think that it will ever get that fast though.
You’re not suggesting that they’re gearing down 2.7:1 and then gearing back up 1:3 are you? What would be the point of that?
But suppose they were.
775-18 free speed is 13000 rpm.
13000/2.7*3 = 14444 rpm.
So if the output is 10000 rpm then the 775-18 would be spinning at 69% of its free speed. It would be pulling 28 amps and burning over a hundred watts of waste heat. (I’m assuming here that the OP meant 10000 rpm at 12 volts; maybe that’s not what he meant).
In any event, the tangential speed of an 8" diameter wheel at 10000 rpm is 238 miles per hour.
We had ours at about that speed, and we realized we really don’t need it. You should be at something around 20 Feet/sec to be making half court shots. Having them too fast makes them draw more power, and raises the spin up time for repeating shots. Furthermore, it makes your realm for adjustment considerably lower. I would suggest changing your gearing, if you can.
Our dual 775’s running through cim-u-laters freespin our 8" wheel up to just over 3600 RPM, as measured with a photo-tach. Works out to about 125 fps, or 85 MPH. We use around half power to shoot from the key, but since we’re using a single axle we only get half the wheel velocity as ball velocity (the rest is backspin).
At full power it’s max range was right around 30 feet. We’re using a high angle fixed hood, so it’s not optimized for max range.