Ironduck

Sultan: Theory about the difference between the G meter and the Performance Box GPS: I can only speculate. Maybe they are using a longer data averaging time. I used 1/2 sec which corresponds to roughly 12-15 feet which is about as long as minimum radius part of many turns. Maybe the G meter is filtered or programmed in a way that gives a lower result. Low Rider: Max Speeds: I did not pay much attention to that as it generally occurs in a long relatively straight run. <o></o> <o></o> Menno: GPS Action Replay and other analysis programs: I have used them for displaying sailboat tracks and they are great for that.The Performance Box comes with similar software. Unless the GPS is faster than 1 Hz (one measurement/sec) you typically only get a couple points in a turn. This is not enough to reasonably resolve the shape and size of the turn <o></o> Bob<o></o>

At the 2010 SES I collected a bit of data on the lateral acceleration we achieve when carving. Since SES 2011 is right around the corner it is more than past time for a quick report. I made most of the measurements with a 10 hz Performance Box GPS. I checked a few turns by measuring the radius of curvature of the track several places along the turn (With the GPS speed, this is another way to calculate acceleration). The GPS accelerations agreed with the acceleration calculated from the GPS track and the measurements of the real track. I did several comparisons between the G-Meter that Fin had and the GPS. The G-Meter averaged 30% lower than the GPS. 1) In harder turns most of us are getting about 1.4 g laterally. 2) For the most part, the more skilled riders went faster but had a similar lateral acceleration to the less skilled control (me). The speed difference in harder turns was 28-32 mph vs 21-23 mph. 3) Bill Sauer was turning harder turns than anyone else on the G-Meter. The highest reading I got for him was 1.67 g on the GPS (1.25 on the G meter). Trent was close at 1.65 g. <o></o> See 3/8/08 post for a more detailed post on what the GPS data looks like. Bob PS: I will not be at the SES this year so I won't be pestering anyone to carry my pack down the hill.

I am happy to report that the Coiler 178 FC has found a happy new home. Thanks, Bob

I will be attending the first part of SES09. I have a room booked in Carbondale for 2/6-2/9 ($90/night-2 beds). If anyone needs accommodation for that period I will be happy to share. OR if anyone has a similarly priced space up valley or wants to share a room down valley, I will be happy to share ( Dan, is your space still available in Snowmass?). Thanks, Bob

Captain, I am home and I still have it...give me a call or send an email. Bob

Hotbeans, I had it set up at 19", centered, 67 and 62 deg. (size 11 boots). What do you recommend? Bob

I bought this board a year ago and made less than 10 trips down the hill. I have found it is a bit stiffer than I prefer for the relatively narrow trails I ride in northern VT. I am 175 lb and 60 yrs. It hooks up nicely and turns well. The previous owner only rode it a few times as well (he is even lighter than 175 lb). It is in excellent condition with one 3/4" long by 1/16" deep chip on the edge of the top sheet (see picture below). The base, as you might expect for so little use, is pristine. The specs are 178 FC 05 RS1 6.75. The waste width is 18.7 cm. The sidecut is 10.5 M. From the specs Bruce can tell you more. Asking price: $350+shipping. If you are in Aspen and contact me before 9:00 AM on 1/22/09 we can avoid the shipping. After that I will be in Northern VT. Email with questions or comments. If you would like a reference, I suggest Jack. Thanks, Bob Dill <!--[if !supportLineBreakNewLine]--> <!--[endif]-->

This looks like an interesting method but there appear to be a couple of differences for what we are doing. In particular the turn rate is quite high (roughly 1.6 turns per second). Presumably this is in soft snow and the turns are quite short radius. 2+Gs seems pretty high to me for a sustainted turn (but perhaps not so high for a brief inpulse). I will see if I can get more details from the author of the article. Bob

A number of approaches to measuring lateral acceleration have been suggested. Accelerometers are tricky to use properly in an application like ours with the vibration/chatter and changing body angles. Trying to get a reasonable estimate from speeds, side-cut radii, body angles, etc. is pretty hopeless. You have to combine too many assumptions and estimates. As an overall constraint, ‘Thumper’ makes a good point: we are only so strong. That certainly limits us to less than 3 g. <!--[if !supportEmptyParas]--> <!--[endif]--><o></o> These days, automotive performance is commonly measured with fast GPSs. The Race Technology DL1 that ‘cory_dyck’ mentioned is a good example of this. I have a similar unit: a Performance Box from Race Logic. It records data at 10 hz (10 times/sec). Its software calculates lateral acceleration. In January I got a bunch of data at Buttermilk. A typical example is shown in the following jpegs. The first is the track of the GPS antenna. Compensating for the antenna being on the helmet rather than at the center of gravity or ‘center of muscle effort’ adds about 0.1g. The second picture is of the speed (red) and lateral acceleration. The zaggy character of the graphs should be smoothed by eye to get a reasonable estimate of the peak acceleration. In this example the toe sides are about 1.3g (before adding 0.1 for the antenna position). Positive acceleration numbers are for clockwise turns (regular-toe side). The heel sides are about 1.0 g over the four turns. I also have examples of heel sides in the 1.3 range. I am not the most powerful carver around so I expect some people may be able to approach 2 g. Overall for the hundreds of turns I measured, typical hard turns are about 1g. Speeds in the turns ranged from 20-28 mph. Turning radii were 25-40 ft. On a related note, when I let the board run, I rarely exceeded 32 mph. <!--[if !supportEmptyParas]--> <!--[endif]--><o></o> Simple and fairly accurate measurements can be made with a logging GPS and a tape measure. Email me for details if you are interested in trying this. It is not hard to do but to be reasonably accurate, it needs to be done right. Alternatively, I ride at Sugarbush North (Vt). If you are in the area, get in touch. I have plenty of duct tape for antenna mounting. <!--[if !supportEmptyParas]--> <!--[endif]--><o></o> <!--[if !supportEmptyParas]--><!--[endif]--><o></o> Bob

The GPS measures speed from a doppler calculation on the signals it is getting from satellites seen from many angles. These satellite speeds are on the order of 5,000 mph and the GPS can measure speed with an accuracy of 0.2 mph or better. If it is smart enough to do that, it should have little difficulty dealing with a little elevation change. Bob Dill

Radar works pretty well for speed measurement but my experience with it is that it is no fun when what ever you are measuring is hurtling at you, out of control, at 50+... I have had a hard time convincing people that they don't need to risk their life and mine by running too close to the gun to be sure the speed is measured. A good gun will pick up a person on a snowboard 1/8 mile or more away. A couple of alternatives: A GPS on the board (or rider) alleviates the need to have anyone in the line of fire and it lets the rider pick when and where he wants to go fast. If you are using radar, it works just as well from behind as in front. If you are going to be in front then a tree in front of you might be a good idea. Or mark a course that keeps the measurement guy at a safe distance. A voice recorder or video camera is handy for recording the speed data. <!--[if !supportEmptyParas]--> When you get some data , please share it.<!--[endif]--><o =""></o> Bob

Gleb, I have done a bit of work with using GPSs for velocity measurement. All the Garmin units are pretty good. A $100 Etrex will work as well as a $400 GPSmap 76. They both record MAX speed accurately. What they don't do so well is log your speed and position over multiple points. The track log is OK but the speed data is irregular (generally at least several seconds between track points) and, with some units, it is considerably less accurate. The Geko is a little smaller than the Etrex, costs a little more but should have the same GPS engine. Both are reasonably waterproof. As an alternative, Delorme sells a logging gps called a Bluelogger for $149 bundled their StreetAtlas software (an Etrex with a data cable will be nearly as expensive). It records date, time, position, velocity, altitude, heading and signal quality every 2 seconds. It will record 50,000 data points (over a day at 2 second intervals). The battery will last 10 hours in warm temperatures although I am not so sure about cold conditions. It is not waterproof so a plastic bag or box may be necessary. The bluetooth connection can be a pain for BT illiterate people like myself. The data is accurate (speed measurement uncertainty is better than 0.2 mph-same as Garmin). The 2 second interval gives frequent enough data points that you can make reasonable estimates of things like lateral acceleration and turn geometry. You can put the data on their mapping software if that is of interest. I usually load it into a spreadsheet for analysis. <!--[if !supportEmptyParas]--> <o =""></o> Another logging possibility is using the Etrex or other GPS and hooking it to a Palm Pilot running Cetus software. This involves more money if you don’t already have the Palm. Getting good data requires a good view of the sky. Most jacket pockets don't work so well. Taping the GPS to the board should be pretty good. Taping it to your shoulder (even inside your jacket) might be fine as well. Logging has an additional advantage. If you have bad data it will be apparent from the log. Either the data won’t change from point to point or it will change abruptly. The number of satellites in view will generally be less than 5 if this is happening. <!--[if !supportEmptyParas]--> <o =""></o> Let us know what you find. <!--[if !supportEmptyParas]--> <o =""></o> Bob