I was just thinking on the topic of modding non vex motors to be vex compatible and I had quite and interesting idea.
I have a 4500psi 88ci tank with a regulator to take the pressure down to 150psi and a 90psi 23,000rpm husky cut off disk.
The cut off disk is very small about the size of a dremel but it packs a punch, 2/3hp at 23,000rpm!!! With no load
Now if I hook up a 3 way solenoid valve between the cut off disk and the tank the vex micro controller can control on and off for the motor.
Now comes the actual motor part, The disk is held on by a single screw so i could do the same with a gear by drilling a hole in the gear and screwing it on. Then I could strap the whole thing down very tightly to the vex frame, I am talking pipe fasteners, ties, and everything to keep it straight inline with the gears.
Now assuming all of this worked with full power and no load or resistance and the 5in knobby wheel it would reach a speed of…
4,105.5 MPH
Thats wishful thinking but I believe that with a good size payload 5-10lb this thing might be able to reach say 60mph because any faster and its going to be out of radio range, I don’t really want an out of control 100mph robot with a 4500psi tank onboard. Yikes!!! Not to mention the constant air drain, this thing won’t last more than 1-5minutes at max power.
well, this is theoretically. you did not take into account wind resistance, and the resistance from the bearings. the knobby tires will also cause it to bounce, becoming dangerous at high speeds. if it does (which i’m not saying it will) reach somewhere near that speed, air may get under the robot, lifting it off the ground, and shooting into the air.
I am going to do a small scale test with just the motor and a set of wheels connected to my compressor.
If it works then I can move up to using a c02 tank or hpa tank probably c02 but the faster you use it the colder and more frost that builds up plus the tool was not made for c02 but I don’t think it matters unless the frost accumulates inside.
My pneumatic parts won’t get here for another week (Solenoid valve and Cylinder) but I am getting my hose and fittings today. So I will not be able to mount it for rc use until I can get those parts.
And as for it lifting off the ground well I don’t think that would happen unless there was a good deal of air resistance under the robot. My robot would have many open holes and gaps so I don’t think it would fly.
Friction between a Vex axle and Vex bearings is going to generate a lot of heat at angular speeds like that. The bearing isn’t designed to withstand that much heat…
I just finished making it, its geared for torque at a ratio of 3/7 but it still needs much more work, multiply 23,000rpm by 3/7, you get around 5,000 rpm with a load.
Thats still extremely fast and I want to cap it between 800-1000rpm so much more gearing is in order and the torque at 5,000rpm is not that much but the more I gear it the better.
This is starting to look like a very good motor for a stationary machine but it Is going to be a real challenge to fit this unit on a robot. It may not even be possible unless I Increase the pressure above 90psi but the higher you go the chance of the motor failing increases as it was designed for 90psi.
Here are some pictures, they were taken from a webcam so they suck but it will give you a general idea of what I did. Keep in mind I was not trying to destroy my tool so I used ties and tape to secure it but in a future version I will use plastic epoxy to bond a mounting block to the motor if it proves to be practical.
When you rev this thing up it sounds awesome, 30psi in the minimum working pressure and it sounds like a mini nitro engine then as you rev it up it starts sounding crazy, I only went up to 80psi but it was really loud at that point so I had to shut it off.
Tell me what you think and any improvements/Ideas, my main goal is to make this portable!
Yea, I will gear this down a lot more this was just to see if it could work so now I can go with a 1/24 gearbox so I will get about 900rpm which is only 14mph.
Wait a second, Correction, I want at least 30mph probably not 60 because thats insane but 30 is alright. At 60mph I would need 4000rpm at an alright torque which is hard to get.
I will need about 2000rpm for that but keep in mind that I could probably jack this thing up to 150psi before risking any major damage to the tool which will increase its power so that 30mph is possible.
Do you guys think it might be possible to use a c02 tank? I only ask because they are small and walmart offers exchanges, the paintball shop here is like 30 miles away now factor in gas its almost $12 to go there and back plus $5 for the hpa fill so a 1 mile trip to walmart and a $4-5 exchange is easy. The reason I have doubts is because it gets very cold when you draw a lot of c02 out of it and I don’t want the motor freezing up or the solenoid valve freezing.
