Yeah, having looked into ways to set up photogates to accurately capture time to stop, there is no way to make it practical for a volunteer event crew, and a limited/reasonable equipment budget. Video, with time showing, would certainly provide a way measure time more accurately than hand timers, but runs into the same equipment cost and trained crew issues as photogates do. It would require for every competition, a suitable camera, and a play-back setup that would allow slo-mo/frame-by-frame play, and that play-back to get the time would take significant time. In both cases, we’re talking hundreds of dollars, and a need for the volunteers running the event to be trained-up to run a complex system. Neither is a workable option.chalker7 wrote:Photogates are wonderful for the teams that travel on a perfectly straight line, however they pose a huge challenge for teams that have any curve or unpredictability. Also, it is somewhat challenging (but not impossible) to time when something comes to a complete stop with photogates. They're mostly useful for timing when something passes by on a track (like in maglev.)twototwenty wrote: For maglev, photogates are used frequently without, to my knowledge, too many issues. However, they would need to be at the end of the ramp, and would start the time after the vehicle reaches that point, so using them would require a slight alteration of the rules.
That, plus the inherent human error/roll the dice factor in manual timing is the basis for my thought/suggestion (a few posts back) – for next year - to use the distance the vehicle is capable of rolling as a much easier way to precisely measure the same two primary design/performance factors that a run time measures. With all the bright people in the S-O community, someone may well have a better idea, but I really think this approach is worth seriously considering for next year.
Speed (hence time to any given distance) comes from two things, and two things only; 1) how much gravitational energy you get into the vehicle – how far you get the center of mass to fall, given a height ceiling/limit, and 2) how effectively you minimize the energy loss rate (the combination of bearing friction, braking system friction, rolling resistance (tires, trueness of wheels), and aerodynamic drag. Small, but real differences in these factors produce pretty small differences in time (in the 5-10m course distance range)- a few tenths of a second; and that delta range is of the same order of magnitude as the human error/variability in hand timing. That few tenths of a second delta in time to a given distance, however, translates into a substantial difference in rolling distance capability. It is determined (solely) by the same two factors. As I noted earlier, in the vehicles of our two teams, we saw a time delta of ~0.2 @ 5m to 0.4 @ 10m, but we saw a distance delta of 10 meters (20m and 30m); easily, and precisely measurable, and at a scale where much smaller time variability can be precisely measured; 1/100th of a second time delta would translate to 0.5m to 0.25m.
Given the need for a reasonable space requirement for a venue, some reduction in allowable ramp height would be in order. Based on our testing, 75cm is probably in the right range, maybe even down to 60cm; I think our T1 vehicle was pushing the possible performance limits pretty hard- at or above the 90th percentile; I find it really hard to believe anyone could get much beyond 35m w/a 1m ramp and 2.5kg max weight. If anyone wants to check that out, and report back, it would be interesting and useful to know. If the max weight were reduced a bit….2 kg, maybe down to 1.5kg, that would further reduce max roll distance, to where I think a 25m space would safely accommodate everyone. Adding this 3rd run into the ten minute window would ramp up the time pressure a bit (but not too much, since there would be no need to do a precise adjustment of braking distance).
Last, just thinking out loud about ways to “change things up” from this year’s approach, a possibility- in a first run for total distance, allow one team member to be down-course at the target distance line/tape, with a little piece of masking tape. Based on where the vehicle crosses the target distance line, they place that tape piece, and it becomes the target point for the two target distance runs. This would reward precision of build (vehicle and ramp); the degree to which it would run the same line.
Just my thoughts, for what they’re worth…..
