Displaying motor RPM from Spektrum telemetry as MPH.

[Gaz-B]

I'm looking to put the final drive ratio and wheel diameter into the TX to log max speed on the telemetry screen. Probably a job for a lua. Any help greatly appreciated. Gary

[inventor7777]

If you find or code any LUA scripts to allow that, please tag me and let me know as I too could use this.

[pfeerick]

See if you have any luck with this custom mixes Lua script. i.e. save it as rpmmph.lua (the name is not important, but cannot be more than 6 characters), and goes in the /SCRIPTS/MIXES directory on your radio. You will need to turn on "Custom Scripts" under Enabled features either Model or Radio Setup (depending on if you want the custom scripts page enabled for one model, for all). Then go to the Model Setup -> Custom Scripts page, and enable the rpmpha lua. Configure the RPM to be coming from your RPM telemetry sensor. Then adjust the ratio (percentage) and wheel diameter (inches, multiplied by 100 since can only use integers - i.e. 250 is 2.5). There does appear to be a bug in how custom script output is handled... as I need to multiply the result by 10 on B&W, don't need to on colorlcd, and the value is sometimes off by one in the display (i.e. 36 instead of 37), but the output from the Lua itself when printed appears to be correct. Something to play with anyway ;)

You can display the output value "mph" on the telemetry screen on B&W - check under "Lua Scripts" category in the popup menu when looking for it, as well as with widgets on colorlcd.

-- To find mph from the rpm  
-- Take the diameter of the object and multiply it by 3.14 = total feet 
-- Multiply the total feet (diameter in feet) by the rotational speed (rpm) 
-- This will give you a value for feet traveled per hour based on the rotational sped and the circumference. 
-- Multiply this number by 60, then divide it by 5,280 this now converts the mph from the rpm.

-- https://www.omnicalculator.com/everyday-life/rpm    
-- Vehicle speed = Wheels RPM × Tire diameter × π × 60 / 63360

-- where:
-- π is the circle constant; it represents the ratio between the tire's perimeter and its diameter;
-- 60 is the number of minutes (from "rounds per minutes") in an hour (from "miles per hour"); and
-- 63360 is the number of inches (from the Tire diameter) in a mile (from "miles per hour").

-- https://www.rctech.net/forum/radio-electronics/795026-converting-rpm-speed-mph.html
-- Step 0: y = x/12, to convert inches to feet
-- Step 1: Calculate diameter in feet. For example, if the diameter equals 1.2 inches enter 0.10.
-- Step 2: Multiply by "Pi" 3.14159265 (This changes your diameter to a circumference, also called "rollout" in R/C circles)
-- Step 3: Enter the rotational speed of your tire. If your telemetry is telling you motor RPM, then divide your motor RPM by your final drive ratio. Taking into account your transmission ratio and your spur/pinion ratio.
-- Step 4: Multiply by "60" because you need to multiply by 60 to convert from feet per minute to feet per hour.
-- Step 5: Divide by "5,280" to find the speed in mph. You divide by 5,280 to convert from feet per hour to miles per hour.

local input =
  {
    { "Rpm", SOURCE},                 -- user selected rpm telemetry value
    { "Ratio", VALUE, 1, 100,  100 }, -- final drive ratio
    { "Wheel", VALUE, 1, 1000, 250 }  -- wheel diameter in inches (multiplied by 100 to get two decimal places from integer)
  }

local output = { "mph" }

-- Called once when the script is loaded
local function init()

end

-- Called periodically
local function run(Rpm, Ratio, Wheel) -- Must match input table
  local Mph, rpmValue = 0

  if Rpm ~= 0 and Rpm ~= nil then
    Mph = Rpm * (Ratio/100)  -- RPM divided by total geartrain ratio
    Mph = Mph * (Wheel/100)  -- diameter in inches
    Mph = Mph * 3.14159265   -- circumference / rollout
    Mph = Mph * 60           -- feet per minute to feet per hour
    Mph = Mph / 63360        -- inches per hour to miles per hour

    -- print("Mph: " .. Mph)
  end

  -- return Mph -- colorlcd
  return Mph * 10.0 -- bw
end

return { input=input, output=output, run=run, init=init }

[inventor7777]

Ooooo...that looks promising!

[Gaz-B]

Looks good. Will have a play with that. I had a skyrc Bluetooth gps arrive today so can see if it's working. Sent from Outlook for Android<https://aka.ms/AAb9ysg>

…

________________________________ From: inventor7777 ***@***.***> Sent: Friday, August 9, 2024 11:07:55 PM To: EdgeTX/edgetx ***@***.***> Cc: Gaz-B ***@***.***>; Author ***@***.***> Subject: Re: [EdgeTX/edgetx] Displaying motor RPM from Spektrum telemetry as MPH. (Discussion #5370) Ooooo...that looks promising! — Reply to this email directly, view it on GitHub<#5370 (reply in thread)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/AF5PA2CI6YOJD6ZKKNWEGJLZQU4TXAVCNFSM6AAAAABL6FEMGWVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTAMRZGE3TIOA>. You are receiving this because you authored the thread.Message ID: ***@***.***>

[inventor7777]

I have a SkyRC gps and it’s great!