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 Post subject: Re: 2.4ghz cars
PostPosted: Mon 30. Apr 2018 02:46 
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Joined: Sun 13. Apr 2014 01:02
Posts: 308
Location: Sedona, AZ USA
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.


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 Post subject: Re: 2.4ghz cars
PostPosted: Mon 30. Apr 2018 15:35 
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Joined: Mon 9. Nov 2015 11:49
Posts: 153
Location: Norway
Ned wrote:
kiklo wrote:
To get the Delrin balls to work you got to have a good seating, read FREE spinning. They wear fast if stuck.... 3.5 or 4mm is probably the best to use. 2 side mounted work well if Your wire is not flush.

Kim, how do you suggest that 2 balls be mounted along the side of a guide magnet? 3.5mm seems too big. Are the balls available in 3mm which is the same as the thickness of the magnet in the original magracer? What gap do you recommend between the bottom of the guide magnet and the track surface?
Seems to me that a ball on each side of the magnet would significantly limit the distance that the guide arm can swing left and right. This would significantly reduce the maximum steering angle left and right and thus the ability of the car to go around tight corners.
Perhaps one 3mm ball just in front or behind the magnet would work? What do you thinK? Will it really make much difference in lap times?
Please post some pics of your use of the Delrin balls.



I tested with 2 balls as the wire is not flush some places, as the chassis is not with std. front end it does not affect max steering. But I'm not sure it's the best solution. I will bring some laps when I have some to show.
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As for sizes I think you can have them in whatever you'd like.

Best solution is of course to have a perfect track.

_________________
Racing Regards

Kim K.


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 Post subject: Re: 2.4ghz cars
PostPosted: Tue 1. May 2018 02:24 
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Joined: Sun 13. Apr 2014 01:02
Posts: 308
Location: Sedona, AZ USA
I tested an idea today. I cut a .24" dia circle out of duct tape using an old fashion paper punch. Pressed it firmly onto the magnet and guide arm. Tape was .07" thick. Adjusted height of guide arm (and thus the magnet) using nylon insert locknut, until chassis CK8 was running well. The tape resulted in a definite improvement. It reduced friction when magnet crossed over point in track where wire was too high. Also reduced scraping noise. Should reduce wear on magnet and track. Then removed tape. Chassis seemed to run almost as well with little scraping. Apparently tape was useful in setting the optimal height of the guide arm. I will probably continue to use the tape as long as results are satisfactory.

Just in case duct tape isn't good enough, I've decided to design my chassis so that a piece of 0.031" thick Slippery Delrin® Acetal Resin Strip can be easily glued just behind the magnet. It will serve as a skid plate to help avoid contact between the wire and magnet. Will be designed so that plate is about .006" lower than bottom of magnet. Tests today confirmed that 0.006" gap between magnet and paint covered wire is not too big.
This stuff has Coefficient of Friction of only 0.10. $12 worth will last me a lifetime.
https://www.mcmaster.com/#2636t21/=1cn30n8

Photo below shows bottom of my guide arm. Big hole on left is for magnet. Small hole on right is for 0.029" diameter stainless steel pin. Hole between these is for the M2 machine screw with lock nut. I use DesignSpark Mechanical software to make 3D models which can be produced with a 3D printer.


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Guide Arm-11.jpg
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 Post subject: Re: 2.4ghz cars
PostPosted: Tue 2. Oct 2018 19:40 
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Joined: Fri 21. Dec 2012 17:37
Posts: 310
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I have been impressed again by the RCR123 battery which I have been using in the 1/24 car. Despite it's larger size, it is shorter and can be fitted lengthways in the s.w.b. 1/32 cars. Having done this, I have also managed to fit a std. Flysky rx. (without case but with standard connectors) and even a larger servo (E Max ES 9251) which has the standard connector and more substantial splines on the output shaft. I have reverted to masking tape on the four cars which I have running and cars are balanced with a tendency to oversteer rather than understeer. All four 1/32 cars run better on the 1/24 track that the 1/24 car so far. It could take some time to get that right.
Having more grip on the rear makes the cars understeer/overshoot into the barriers with a pretty heavy crash whereas a spin is less damaging.
The lap counter is being fitted to the 1/24 track and we are looking forward to some racing soon.


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