Using a Hot Wheels Radar Gun to Measure The Speed of Quadcopters?

A while back, I got the idea to measure the speed of the multirotors I review. “It’d be great information for the viewer!” I thought. Well, this idea ended up taking me down a bit of a rabbit hole, as evidenced by this video. It’ll not all be RC related, so if that’s what you’re after you might want to skip this one. Rest assured there are many of the multirotor reviews you know and love planned in the foreseeable future! If you wouldn’t mind taking peek behind the scenes though, feel free to take this journey with me! As always seems the case when you really look into something, turns out there are many ways to approach this: The perhaps most straight-forward would be to, just like a car satnav, use GPS to determine the coordinates of the aircraft at regular intervals and then – using some clever math – calculate the speed based on the positions as well as the time elapsed between them. I’m sure there are telemetry solutions that offer this functionality out of the box and – when researching this video – I found at least one stand-alone product, the “Big 5 GPS Meter” that does so as well. As you know though, this channel is about toy grade multirotors, which generally don’t come with, support or – many times – even have the payload capacity to carry GPS equipment onboard. The most hassle-free approach would arguably be to turn to that thing in your pocket. No, not that thing! As the saying goes: “There’s an app for that”. Turns out there are loads of apps for that, but the basic idea is the same: Capture the subject with your device’s camera, then let the app – using some even cleverer math – calculate the speed based on the movement in the foreground versus the background. Now I haven’t tested any of these apps extensively (or at all, for that matter), but do find them to be stretching what can be extracted from – after all – quite incidental and ambiguous data. Under ideal circumstances you can probably achieve fairly accurate results, perhaps not so much when venturing outside the scope (like scale or speed) the developer had in mind. The cheapest approach would probably be to take the science class route: Marking a predefined distance and timing how long it takes the aircraft to travel it, either with something like a stopwatch or – preferably – by recording it, counting the frames and divide that by the framerate of the camera. There are a few practical snags, like the fact that the craft is airborne which makes it hard to determine precisely when it enters and leaves the marked range. Not to mention the fact that it’s quite the operation to carry around and set up, especially if you – like me – was thinking of doing it more than once. Lastly there’s the approach I ultimately settled on, using a radar gun: If you – like me before reading up on all this – are familiar with the concept, but not so much the workings, here comes my brief explanation: A radar gun is basically a portable Doppler radar, a special type of radar that uses the so called Doppler effect to measure the speed of objects. The typical example of the Doppler effect is when a car passes at high speed, either honking its horn or sounding its sirens. It will sound one way as it is approaching and another as it’s moving away. When approaching, the sound waves will be compressed as the object making the sound moves with the soundwaves. When moving away, the opposite will happen. What applies to sound waves also applies to the inaudible, invisible microwaves sent out and listened after by the Doppler radar. The change in frequency (frequency shift) between the waves sent out and the ones – having bounced of the object being measured – received is its basis for determining speed. I hear you saying: “…but wait! Didn’t you say you were looking for an inexpensive solution? Radar guns aren’t inexpensive!” Initially, that’s what I thought as well. My mind may be made up, but I don’t know if it’s all of $200 worth of made up. Turns out there’s one exception though. $20, now that’s on my radar! Enter the Hot Wheels Radar Gun. It’s branding may make it sound like a toy, its design may make it look like a toy and – heck, let’s face it! – it’s intended as a freaking toy, but this doesn’t change the fact that beneath the plastic and bright colors hides a real radar gun. Though not as high powered or high-precision as the ones – for example – highway patrol have, it’s using the exact same principle. The Hot Wheels Radar Gun seems to have been released almost 10 years ago and has since been discontinued, but I was able to find it used on Amazon for $20. Since it’s not exactly a new product, time has allowed engineers and other people with a good grasp of the theory and technology to form their opinion of it. The summed up verdict seems to be “Not bad”, with results close to both more expensive equipment and the actual real-world speed of the object measured. That’s not to say the Hot Wheels Radar Gun will be ideal for the purpose I have in mind. A quick search on Youtube returns a mixed bag, but then I suspect at least some dissatisfaction comes from a failure to understand how the product works and – by extension – how to use it properly. What any radar gun really measures is the speed by which the subject moves towards or away from the gun itself. Thus, to get a proper reading you have to get as close to directly in front or behind the subject as possible. Otherwise, the Hot Wheels Radar Gun is very simple to operate: Just point and shoot at the thing you want to measure. The gun will continuously display the measured speed and when you let go, display the highest measured speed. Below the display you find two toggles, one for switching between miles per hour and kilometers per hour and one – since it’s a Hot Wheels branded product – for switching between real and the Hot Wheel model scale. With the technical and theoretical finally sorted, let’s pack radar gun, multirotors and get practical! I choose four quadcopters, not – mind you – based on their top-speeds but rather on their variety in terms of size and speed, as subjects to test the radar gun with. First out the gate: the Daming DM007 (reviewed on this channel). An in many ways oddly designed, but extremely stable and reliable quadcopter that sadly hadn’t seen much use recently. I figured it’d be a good first test as its slightly bigger size and... Well, not exactly record breaking speed should make it easy to get a read on. …and so was the case, with the radar gun reliably and consistently measuring the quadcopters speed in three out of three flybys. Next up: the Huiying Toys HY-852 (also reviewed on this channel). An – in my opinion – near-criminally overlooked all-round micro that makes up for whatever it may be lacking in top-speed versus the likes of the JJ-1000 or H8 Mini with hard-to-beat handling and durability. Again the radar gun fared well, with three attempts resulting in an equal number of successful and quite consistent measurements. Next up was another Huiying Toys model covered on this channel, the HY-851. A well-rounded nano that since its release has become largely forgotten, probably due to a failure to stick out from the nano quadcopter competition. I’m not even sure it’s still being sold. Measuring the speed of this nano turned out to be the first real challenge for the radar gun. Probably about half of the flybys resulted in no reading, presumably due to the aircrafts small size. In the end though, I was able to get three measurements. Last up was the X1, JJRC’s brushless toy-hobby hybrid. It’s the largest of the aircrafts tested and – by that logic – should be easy to measure. Something else that should be easy is beating the top speed of the other models. The X1 is in a league of its own with regards to power, even when – as a safety precaution – not flown on the highest rate. Strangely the X1 proved the biggest challenge for the radar gun, with most flybys resulting in no reading. Did I, considering the power, unconsciously fly it further from the radar gun as to avoid accidentally hitting my trusty assistant? Is there – akin to those spy planes – something about the shape of the quadcopter that makes it harder to measure? Your guess is as good as mine! Ultimately though, I wasn’t able to get 3 proper readings on camera that time. As the saying goes: “You get what you pay for”. The Hot Wheels Radar gun shouldn’t and probably can’t be compared to devices costing 10 times as much, but I think I’ve shown that, if used correctly and with some patience, it does give readings and pretty consistent ones at that. If you too have an itch to measure the speed of your RC vehicles and don’t mind sacrificing some convenience to make a saving, the Hot Wheels Radar gun may be worth a look. I will continue to play with mine and may eventually provide some sort of speed indication on the fact sheet in future reviews.