RE: New video of my Centaur [TANKS]

["Carioti, John" <john.carioti-at-sensis.com>]

Title: Message

You really need to use the Team Tentacle Torque Calculator to get a good idea how these EV (and other) motors will perform with various reductions.  There is a little bit of guess work involved, but you can get a pretty good idea what you are up against.  I haven't quite wrapped my head around what happens when using treads vs. wheels, but my gut tells me that the Torque calculator works if you simply plug in the sprocket diameter instead of the wheel diameter.  I think that the frictional forces are  higher with a track design- so I put a "1" in the tire coefficient of friction box.  A smooth wheel will almost certainly slip before the motor stalls (e.g. if you bump into a wall), but I'm not so sure about a tank tread.  Especially over grippy surfaces.

 

I plugged in the numbers for a 6:1 reduction and 4.5 inch drive wheel and the current draw for each motor is about 38 amps...which is pretty high. I don't think you want to be running an EV Warrior at 38 amps for very long.  8:1 reduction gives 29 amps per motor which seems to be more reasonable. 

 

Part of the reason the EV warriors work for RC tanks is because the duty cycle for the tanks is probably fairly low- lots of fast movement, then stopping/shooting for a while and then moving again. 

 

With your current tank using the NPC 02246, if you are using the stock 4:1 gearbox from NPC and then reducing again 3:1 with a sprocket, the current draw is a much more reasonable 14 amps per motor (I assumed the tank was also 85 lbs).  An 18 AH battery would last probably 15-20 minutes of 100% duty cycle. 

 

The link for the team Tentacle Torque Calculator: www.architeuthis.net    under the tools bar on the left hand side of the page.

 

Disclaimer: All of the above calculations/speculations are purely my guess and may have no relevance to reality!

 

 

-----Original Message-----
From: tanks-admin-at-rctankcombat.com [mailto:tanks-admin-at-rctankcombat.com] On Behalf Of BrendanKotlanger-at-aol.com
Sent: Thursday, August 24, 2006 10:00 AM
To: tanks-at-rctankcombat.com
Subject: Re: New video of my Centaur [TANKS]

future tank

The next tank for my dad is designed to be about 85 lbs.  I have not received an answer about what gear reduction I should use on it.  At 6 to 1, it would put about 450 inch lbs of torque on the sprocket at 650 rpm. at 8 to 1, It would have 600 inch lbs. of torque at 500 rpm.  This is a rough answer considering I did the calculations 3 weeks ago.  It will be powered from ev-warriors at 24 volts.  This will be a 31 inch tank.  Each track will be a tts 3 inch wide.  4 road wheels on each side.  the drive sprocket will be 4.5 inches diameter.  Can I get away with a 6 to 1 reduction without stalling my motors?

 

current tank

My current tank uses 2 npc-02446 motors with an npc gear box that connects to a 3 to 1 chain drive reduction #35.  The drive sprocket is 4 inch diameter.  My current tank runs at 24 volts with 18 ah in the loop.  The motors get warm after about 5 minutes of runtime.  I still need to do a "kill the batteries" runtime test on it.  The sprocket is calculated to spin at 500 rpm without resistance.  I get the video as soon as I do the test.