Speed measuring?

[SSgt Duramax]

How does everyone measure speed? I used to strap an old GPS unit to my rustler until I destroyed it.

I see some folks maybe use a radar gun? How well does the foam give a radar return? I have a stalker KA radar gun I could buy a battery handle for. I can tag a car a half mile away, and track it for about a mile once I have a lock. I guess I could see if I could get it to pick up my rustler first. It is one of these.

https://copradar.com/rdrspecs/stalkmv.html

Is there any GPS monitoring type of thing that is light? I have a dragy, but it cost $150 and seems kind of heavy, not sure it would stay linked to my phone.

Ideas?

 

[JasonK]

I have a FC on much of my stuff [FPV] and at that point adding a GPS is only like 5g.

for the radar - your likely hitting the wires or battery more so then the foam.

 

[Pieliker96]

Pitot tubes work well, especially if you already have a flight controller to talk to it and record data. There are also some standalone solutions with little LCD displays that'll read out the max speed, probably some tens of grams for each solution.

You could also take an audio recording of a test pass and do some doppler effect maths to get a decent estimate.

 

[L Edge]

Don't know what accuracy you want, but an off shoot of Pieliker96 doppler effect suggestion is to see if your phone has an app using the "doppler concept".

 

[Hondo76251]

Having an actual pitot tube seems to work best for me. GPS is fine but it only calculates speed over ground not actual airspeed. If all you're doing is trying to determine max speed a radar gun will work just fine, though it is still just measuring speed over ground as well.

 

[L Edge]

Having an actual pitot tube seems to work best for me. GPS is fine but it only calculates speed over ground not actual airspeed. If all you're doing is trying to determine max speed a radar gun will work just fine, though it is still just measuring speed over ground as well.

Interested in your pitot tube concept. What software package and what's the % error? Does the company have a web site?

 

[Jade_Monkey07]

I use the doppler method. It's as easy as taking a nice fast low pass over your phone while recording audio and popping the audio file into an app, clicking a few things and it pops out a number. The Info I've seen on this compared very closely to the radar gun they were also using when testing.

 

[Hondo76251]

@Jade_Monkey07 thats interesting, never thought of that. Crazy what these new fangled devices can do! Lol

@L Edge ive had a few, cant remember which one came from where, Amazon and banggood. The ones ive had work great (proper placement in clean air is important) I've always run them on pixhawks.

https://www.amazon.com/dp/B01M6902BF/?tag=lstir-20

 

[Jade_Monkey07]

@Jade_Monkey07 thats interesting, never thought of that. Crazy what these new fangled devices can do! Lol

@L Edge ive had a few, cant remember which one came from where, Amazon and banggood. The ones ive had work great (proper placement in clean air is important) I've always run them on pixhawks.

Heres a video comparing all the methods.

 

[PsyBorg]

Depending on accuracy you need or want simple distance over time works too. Measure and mark a set distance and time the crossing of each line. Many ways to do it.

 

[Hondo76251]

Yeah, thats a neat comparison, though hes not exactly correct about the pitot measuing upwind vs downwind differently. If he was doing his run downwind (and it sounded a little breezy) it would stand to reason that his speed over ground readings would be higher than his indicated airspeed via pitot sensor.

If a model can fly at 30 mph, and it flies into a 20 mph headwind, it will have an indicated airspeed of 30 mph and a ground speed of 10. When it turns downwind it will then have an airspeed of 30 mph and a ground speed of 50 mph.

 

[Jade_Monkey07]

Yeah, thats a neat comparison, though hes not exactly correct about the pitot measuing upwind vs downwind differently. If he was doing his run downwind (and it sounded a little breezy) it would stand to reason that his speed over ground readings would be higher than his indicated airspeed via pitot sensor.

If a model can fly at 30 mph, and it flies into a 20 mph headwind, it will have an indicated airspeed of 30 mph and a ground speed of 10. When it turns downwind it will then have an airspeed of 30 mph and a ground speed of 50 mph.

Yeah you are correct there. I mostly fluffed over the pito tube stuff since I have no room to squeeze one into my micros haha

 

[Hondo76251]

Yeah, id think GPs on those might be best, though I've had pitot on a tiny trainer for a while lol