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Just wondering how I can either measure or estimate my top speed? I have a mamba max pro, 8400 mah ni-Mh battery and a 4600 kv motor, full bearings.

I have to guess that it's somewhere around 30 mph - but wondering what the RC10 ran stock with a 6 cell back in the day with bearings?

Well some have used a handheld GPS or a Car type GPS attached to the car, gives you a rough estimate. I think Toys-R-us used to have a cool Speed / Radar gun contraption that seemed to work too.

I saw something that looked like some kind of an app on an iphone or ipod touch in a car that went 70+ mph. I just want something like a radar gun that would work. Do any of the new radio / transmitters that have telemetry send speed back to the transmitter?

Yes. Spektrum Dx3s, for one.

Not all that accurate, but you could do a speed trap. Two lines across the road, measure the time to traverse, and do a little math.

Example:

100ft trap, 6 second pass.

(100ft/6second) * 1mile/5280ft* 3600sec/hour = 11.4 Mph Slow example!

Keep in mind that flat out speed doesn't always mean much. When I used to race stock years ago, most cars averaged like 12-14 MPH for a 4 minute race. Speed is ETREMELY realtive to the space that you are running in. 25 or 30 MPH sounds slow, but on a track with a long straight of 60-80ft it's another story.

Ah ha! After I posted this I figured I could do this but I didn't know how to do the math. Thanks

Keep in mind there is at least 25+% error (probably much more) timing across 100ft - and the % error increases with higher mph.... i.e. human error starting and stopping the watch right on the line - depth perception from 100ft away etc - especially if you are trying to do it yourself. Best you can do is a range of possible mph.

I was looking at the Spektrum site and it appears the 2xs and 3xs both have speed telemetry. Anyone tried this? On a side note, there is a radar speed gun app for iPhone and iPad so I may just do that

RC104ever wrote:On a side note, there is a radar speed gun app for iPhone and iPad so I may just do that

I hope they don't have to be on-board to work! You wouldn't want me driving your car on a high speed run with your Ipad strapped to the roof! A handheld gps is very accurate. My cousins and I clocked a Pumpkin at 57 with a 9t and 10 cells. 10 more cells strapped to the front bumper to keep it down. Did it wobble at 57 mph? You betcha! Rolled it about 30 times. Luckily the gps was inside. That was back when there was plenty of spare time to do stuff like that.

These days I honestly prefer a bag motor in everything. Guess I'm just getting old.

I tried one of those Hot Wheels radar guns, never had much luck with it and lost interest.

The Spektrum telemetry is only a calculated speed based on measured RPM and the tire size you input as I understand it. Problem is it doesn’t account for tire slippage, remember nearly the entire power of the motor is working on those little patches, I suspect most don’t realize how much tire slip there is at full chat. (I work in the rubber biz) On the other hand, doesn’t grab tire growth, which can be dramatic with soft tires and lots of motor (aka pizza cutters ).

Strapping a GPS on seems to be the most common method.

The lines on the road gives me an idea, don’t know if it’s a good one though. Spektrum has a gizmo that triggers the telemetry when the car goes by, wonder if 2 of those could be used for timing? Basically will it work with 2 units?

Or just go old school (which, given where we are chatting.... ), have your buddy drive the full scale car, ride shotgun and chase your RC! Just make sure your bud understands the battery dumping concept….

Dave

Dave, great minds think alike! I had thought of having my son drive the RC while I chase it. Problem is I don't think my neighbours would approve

I was digging on the app store and found a couple 99 cent apps that may work. Failing that maybe I should just go buy a used radar gun on eBay, lol

I saw on another forum using a video camera and video editor over a measured distance and counting the frames (i.e. 30 frames per second)....better than eye and stopwatch....I would say. Again depth may be an issue though - i.e. wide angle over 100ft to determine exact crossing of both lines.

losiXXXman wrote:Not all that accurate, but you could do a speed trap. Two lines across the road, measure the time to traverse, and do a little math.

Example:

100ft trap, 6 second pass.

(100ft/6second) * 1mile/5280ft* 3600sec/hour = 11.4 Mph Slow example!

Keep in mind that flat out speed doesn't always mean much. When I used to race stock years ago, most cars averaged like 12-14 MPH for a 4 minute race. Speed is ETREMELY realtive to the space that you are running in. 25 or 30 MPH sounds slow, but on a track with a long straight of 60-80ft it's another story.

So I did a 60.5 ft speed trap. Used 60.5 ft because the iPad app was for a baseball radar gun (which didn't work). I then switched to old fashioned stop watch. I did 3 runs and had results of 2.1, 1.8 and 2.0 seconds.

So using an avg of 1.97 secs:

Gives me a speed of 20.94 mph. Seems slow as that translates to 33.92 km/h and I'm sure it's faster than that. When I used the radar gun program I was getting 200 mph ish speeds which if you divide by 10 then that would seem to make sense.

I can't see how something like a Slash would go 45 mph out of the box! I need better tires for sure and I will swap the longer front control arms onto the car for better control.

What motor, battery, tires... Etc?

Motor - Castle 4600 kv brushless
ESC - Castle Mamba Max Pro
Battery - 8.4V Ni-Mh
Tires - worn out Losi knobby off road rear and the offset rib tire in the front
Wheels - some kind of dish 2.2" front and rear
Suspension - OEM shocks and springs with 47.5 weight silicone oil in the rear and 27.5 silicone oil in front
TX / RX - Futaba Magnum Jr. AM TX / RX 75 Mhz

I am still waiting for my Castle Link so I can fiddle with the factory settings a bit.