Re: 2.4ghz cars
Posted: Mon 30. Apr 2018 02:46
In my opinion, the key to effective performance of the system, is the correct gap between the top of the wire and the bottom of the guide magnet. The lack of a gap at spots in the track affects acceleration, deceleration, top speed, and power consumption. If the gap is too big, guidance by the wire in the track is compromised. The gap between the top of the lane change plate and the bottom of the guide magnet is also important for reliable lane changing. Other factors also affect the reliability of lane changing.
Of course, we are not able to maintain a constant gap in practice. Wes’s method is probably best at achieving a fairly uniform gap for a non-portable track used only indoors. His method won’t work for a track like mine which is permanently outside and subject to great variations in solar radiation, ambient temperature, humidity, wind, snow, rain, bugs, dirt and dust. My track also has bumps, cracks, pot holes, and banked corners. Maintaining a constant gap everywhere on my track is impossible.
As best I can tell, on average I have about .005” of paint covering the .032” diameter wire and rigid foam track baseboard.The wire is embedded in the track baseboard and it is as flush as I can make it. I estimate that the clearance between the bottom of the magnet in the guide arm and the paint over the wire averages .008” throughout the track. That implies that the average gap between the magnet and wire is .013”. I suspect the range is .003” (where the magnet scrapes thin paint over the wire) to .018” where the wire is too deep. A gap of .015” definitely works on long straights but may be too much on corners. For comparison, a sheet of cheap computer paper measures about .002”. Now that most of my track has weathered for 3 years, there are many places where the magnet scrapes the paint above the wire. There are only a few places where the wire is too deep causing an excessive gap and loss of some guidance. (Keep in mind that my wire dia is 0.32” and the guide magnet is 4mm dia x 3mm thick.)
Like Wes, I don’t think that a hinged guide arm will work. But I am interested in trying a roller mounted just behind the magnet in the current guide arm I use, which is similar to one designed by Wes. I’m looking for a 3mm diameter x 4mm long roller with a hole running down the center of the roller the full length. The idea is to mount this so that the roller is perpendicular to the wire and the bottom of the roller is .005” lower than the bottom of the magnet. Most of the time the roller would not touch anything. In theory, the height of the guide arm would be adjusted so that the roller would only touch the track when the painted wire is more than .005” above the track surface supporting the front wheels. This should help to reduce the frequency and magnitude of the problems caused by the wire being too high.
To work properly, I figure that the diameter of the roller must be constant +/- .001” (.025mm). The hole must be precisely centered within the roller, +/- .001”. Ideally the hole diameter would be .8mm, but I could make 1mm work. The roller should be very hard and abrasion resistant but lightweight. So far I haven’t been able to find such a roller.
As an alternative, I plan to try a replaceable skid plate made of Delrin or UHMW mounted just behind the magnet. (There’s not room in front.) Again, I’d mount this so that the bottom of the skid plate is about .005” lower than the bottom of the magnet. This should greatly reduce the amount of time a guide magnet scrapes the wire during a race. The problem with this idea is how to make it easily replaceable. And of course, I am assuming that the friction between the skid plate and wire would be less than between the magnet and wire. If not, it wouldn’t help.
If you build your track indoors, and use Wes’s plastering method, I don’t think you have to worry about this. Just keep the plaster smooth, flush, and level with your wire, the width of the roadway.
Of course, we are not able to maintain a constant gap in practice. Wes’s method is probably best at achieving a fairly uniform gap for a non-portable track used only indoors. His method won’t work for a track like mine which is permanently outside and subject to great variations in solar radiation, ambient temperature, humidity, wind, snow, rain, bugs, dirt and dust. My track also has bumps, cracks, pot holes, and banked corners. Maintaining a constant gap everywhere on my track is impossible.
As best I can tell, on average I have about .005” of paint covering the .032” diameter wire and rigid foam track baseboard.The wire is embedded in the track baseboard and it is as flush as I can make it. I estimate that the clearance between the bottom of the magnet in the guide arm and the paint over the wire averages .008” throughout the track. That implies that the average gap between the magnet and wire is .013”. I suspect the range is .003” (where the magnet scrapes thin paint over the wire) to .018” where the wire is too deep. A gap of .015” definitely works on long straights but may be too much on corners. For comparison, a sheet of cheap computer paper measures about .002”. Now that most of my track has weathered for 3 years, there are many places where the magnet scrapes the paint above the wire. There are only a few places where the wire is too deep causing an excessive gap and loss of some guidance. (Keep in mind that my wire dia is 0.32” and the guide magnet is 4mm dia x 3mm thick.)
Like Wes, I don’t think that a hinged guide arm will work. But I am interested in trying a roller mounted just behind the magnet in the current guide arm I use, which is similar to one designed by Wes. I’m looking for a 3mm diameter x 4mm long roller with a hole running down the center of the roller the full length. The idea is to mount this so that the roller is perpendicular to the wire and the bottom of the roller is .005” lower than the bottom of the magnet. Most of the time the roller would not touch anything. In theory, the height of the guide arm would be adjusted so that the roller would only touch the track when the painted wire is more than .005” above the track surface supporting the front wheels. This should help to reduce the frequency and magnitude of the problems caused by the wire being too high.
To work properly, I figure that the diameter of the roller must be constant +/- .001” (.025mm). The hole must be precisely centered within the roller, +/- .001”. Ideally the hole diameter would be .8mm, but I could make 1mm work. The roller should be very hard and abrasion resistant but lightweight. So far I haven’t been able to find such a roller.
As an alternative, I plan to try a replaceable skid plate made of Delrin or UHMW mounted just behind the magnet. (There’s not room in front.) Again, I’d mount this so that the bottom of the skid plate is about .005” lower than the bottom of the magnet. This should greatly reduce the amount of time a guide magnet scrapes the wire during a race. The problem with this idea is how to make it easily replaceable. And of course, I am assuming that the friction between the skid plate and wire would be less than between the magnet and wire. If not, it wouldn’t help.
If you build your track indoors, and use Wes’s plastering method, I don’t think you have to worry about this. Just keep the plaster smooth, flush, and level with your wire, the width of the roadway.