measuring speed

[studysession]

Anyone use these bushnel radar guns?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=16032&item=7115393956&rd=1

I have written RC Driver and a few brushless manufactures and asked them what they use for measuring speed on their RC products and they said they use this radar gun.

I have been using a Venom Speed Meter - now I have 2 cars that the VSM does not properly mount. I will NOT do the GPS thing. I have my own reasons for that.

Want an afordable radar gun and thought if these brushless manufactures use it and if RC Driver people emailed back saying to use it. Figure it can not be all bad.

Anyone use it before?

[TheSteve]

I use a Bushnell Speedster to verify all reported speeds, it works great.

[studysession]

Cool - I am thinking around Christmas or beginning of january I will get me one of these.

I now just need a more wide open area for doing speed runs again. Just want to make sure I try more than just the VSM for measuring the speed. I am not going to add the weight of a GPS to my speed cars.

[TheSteve]

Sounds like a plan. I really don't trust the VSM for measuring actual speed unless calibrated against a radar gun or GPS. The VSM can of course be used to measure relative speeds.

[studysession]

I feel the same. It gives more of an approx not 100% accurate. Last real speed run I did 93MPh - That was early this year when I did that. I have not done real speed runs in a long time.

I think I am close to breaking the 100MPh mark. Want something more accurate for measuring speed.

Right now with setup I have it should do over 100MPh. But need to finely tune the car now and get it ready. When I do the actual run - I want to be in a more open area. When I did the 93MPh run, I lost control and hit a curb. There are not to many open areas close by me.

So not sure where I will do the run.

[OptimaMan]

I did the GPS, and Bushnell radar thing and they're within 1 mph of each other. Only think with Bushnell, sometimes, it gives me a funky number that is way faster or slower than it is so you might have to do a couple of runs to make sure it wasn't a false reading. One thing good about these systems is that they are actual measurements. Venom and Eagletree are good... but as tires balloon, they'll actually underestimate speed and the speed is only as good as you are able to measure the tires accurately.

[studysession]

Not only the tire ballooning but also if a tire slips and loses traction. How accurate is that with a free spinning wheel for a couple of seconds.

The ESC that I installed in my ESC is set to allow me to get maximum acceleration. With the gear ratio and motor I am using for this run, I am sure that I will get some wheel spin. Foams or rubber will not matter. The acceleration is so hard that I keep losing some traction. So I was thinking for the cars that allow it, leave the VSM installed and on all of them use the radar gun along with it or without the VSM if the car does not allow it to be installed.

Hope that makes sense. I am using some very high torque motors in my speed cars. I am a couple of new cars coming and I am designing on my mill and lather new differentials for them to allow higher gear ratios. All my diff/tranny stuff is completely custom.

I just want a more accurate method of measuring the speed.

[OptimaMan]

You could also use an Eagle Tree system with telemetry (Seagull). You simply input the pinion and spur and the transmission ratio. Then you put in the dire diameter - if you use foams, the expansion is negligible. As you run your car, you'll get actual MPH measurements on your LCD real time! The whole setup will cost you about 400 bucks though.

[Craps]

Here is the link to Eagle Tree: www.eagletreesystems.com

I am getting ready to get the Seagull system and with all the sensors I will use, the cost is closer to $600. Real Speed in Real Time!