Air compressor on robot


#1

Are you allowed to wire up the air compressor on the robot directly to a motor controller or the pdb? The reason why I am asking is because the air compressor that my team is probably going to be using on our robot has a different wire gauge on it. It is not the stock air compressor. When we use the air compressor through the pnumatic controll module, we think that it is not getting enough power. This is this air compressor. https://vixenhorns.com/product/vixen-horns-vxc8701-150-psi-air-compressor/ We would like to be able to hook it up to a motor controller or the pdb so that we would be able to use the right gauge of wire and get enough power to the air compressor.
If we are able to wire the air compressor up to a motor controller or the pdb what type of sensors would you use to shut off the air compressor when it gets to the right pressure and not have over 120 psi in the main tank?


#2

See table 10-2 and R37

R86 also states compressor rules you should read.

Can’t stress this enough - go read the manual.


#3

@Al_Skierkiewicz, please chime in here…

So, here’s the notes on stuff we’re working with.

  1. You have two options for powering the compressor: PCM, or using a relay from the PDP with a 20A breaker. If you can put proper-gauge wires between the wires on the compressor and the PCM that will also work to make the connection.
  2. You’ve got one he** of a current draw on that compressor. 18A will drain your battery in 1 hour. That’s probably why you’re thinking you’re not getting enough power, it’s a high-amperage compressor. Remember that you only get 20A breakers on the compressor line. (Ignoring the built-in 30A fuse as that is legal because it’s built-in.)
  3. Sensors: You still need the Nason pressure switch, read R92 for instructions.

I would proceed with caution if using that compressor at all…


#4

I just want to clarify this. This is mostly true, but if you use the Automation Direct 40A relay, you are allowed to use a breaker of up to 40A to gate it, according to the manual.


#5

We are allowed to use the “Spike” relay to power the compressor, please see R36-B, for up to 20 Amps. We must use the specified air pressure switch, please see R92. The Spike is controlled by a roboRIO relay port, and the pressure switch is wired into any DIO roboRIO port configured as a DigitalInput. The switch reads 0 (closed) when the air pressure is low, and 1 (open) when the air pressure is ~120 PSI. Your code should turn the pump on in the 0 case and off in the 1 case.

This is why the pump will stay off if the pressure switch is disconnected - an unconnected DigitalInput will reliably read 1.


#6

Thanks Eric,
Here is what you have, a compressor very similar to the large ViAir compressor. Be aware that this compressor (as with the large ViAir) uses a stainless steel hose and check valve that must be attached when used on your robot. I suspect that you have not installed the hose and check valve. Without the check valve, the compressor cannot build pressure and runs virtually constantly. The check valve prevents stored pressure from reentering the compressor during the intake cycle as there is no internal valve assembly. The stainless steel hose is required by the manufacture due to the high temperature output of the compressor during operation.
The PCM will work with the check valve in place. However, you can use either the Automation Direct Solid State Relay or the old Vex Spike. The start current on this compressor is 18 amps but run current is lower than that. I could find no manual or spec sheet on the linked page but I would suspect that the run current would be in the range of 10-12 amps.
The wire used with a 40 amp SSR is dependent on the wire used with that branch. Please see the wire rules that relate to current protection for branch circuits.
I highly recommend you use the PCM at this point. If the supplied wire is to large a gauge for insertion in the PCM, you can use #18 wire to extend the compressor wiring and connect to the PCM. You can use a dedicated output on the PDP with a 20 amp breaker in place to power the PCM or the SSR or the Spike using the correct gauge wire size. I recommend all teams use a PDP output to feed the PCM. This will prevent blowing the 20 fuse on the PDP if you use the output at the end of the PDP. The self resetting breaker will prevent compressor failure in a critical match (i.e. on Einstein)


Air compressor fittings
#7

Here is a picture of the prototype that me and my team made to use with the air compressor. Would we be able to use this pnumatic hose on the robot attached to the air compressor with brass and steel fittings


#8

Unlike most of the robot rules, pneumatics rules list specifically which parts you can use.

It looks from the picture like that tubing has a larger outside diameter than 1/4" nominal, which means it does not fit in R84D. Unless the tube is part of the compressor allowing it through R84K, it is not allowed. If you do try to use that tube with R84K, expect to have to show that the tube came with and is part of the compressor.


Air compressor fittings
#9

The hose must be used with the compressor for it to function. As Al mentioned that hose contains the unit’s check valve, specifically the end with the large silver “fitting”. Reinstall that to the compressor head and make your initial connection to the safety valve and other required components after the compressor’s hose.


#10

This is where I point y’all back up the thread. Al’s look is that that hose is legal as it is part of the compressor.

Which means that NOT having it properly attached to the compressor per manufacturer is Right Out, and that’s not how you’re currently set up. You need your release valve, dump valve, and pressure switch on the OTHER end of that hose, which should be directly into the compressor. @Jon_Stratis can probably help you better than Al or I can as far as an in-person visit.


#11

@ Stellarsimba7800 - You need to hook up the hose exactly as it shows on the product page you lined at the top. That means the hose you’re holding sits between the brass fittings and the compressor.

My team is using a similar compressor (it’s a Viair, but it has a similar hose setup). I’ll take a picture of it set up properly on Monday for you. If you want an in person visit, let me know. If nothing else, I’m sure I’ll see you at one of the week-0 events in two weeks!


#12

Those above are correct but to add a little to the discussion. With this particular compressor, the manufacturer requires the hose be attached to the compressor mostly because the outlet temperature is so high. In my mind that means that compressor with the hose attached per the manufacturer is a single assembly. I know it doesn’t seem to make a lot of sense but it is the only way we can effectively inspect this compressor for all teams that use it. The hose and compressor are one single unit. The check valve I discussed earlier is part of that hose assembly and is required for proper operation of the compressor. The check valve isolates the compressor from the pneumatic system. The pneumatic rules also are written for safety and the proper operation of this compressor when used with the robot pneumatic rules will minimize any safety issues associated with 120 psi compressed air.
When inspectors see this compressor, they should immediately look to see that the stainless steel hose is attached. Until the hose is in place, pneumatic inspection should not continue.


#13

BTW, If you were to connect everything as shown with the hose downstream, the pressure relief valve and pressure release valve and the pressure switch would not work as intended.


#14

Agreed. With the check valve downstream of the relief/release valves, opening them won’t actually let the pressurized air out of the remainder of the system.