Re: Questions about past email and other things [TANKS]

[Joe Sommer <anvilus9-at-adelphia.net>]

At 08:49 PM 3/1/2005 +0100, Rodolphe GREMEAUX <r.gremeaux-at-wanadoo.fr> wrote:
>i've some question about this email
>
>         Most current tanks use about 4 inch diameter drive
>         sprockets turning at about 400 rpm.  That produces
>         4.76 mph.  I estimate that you need about 400 in-lbf
>         sprocket torque per track to perform a full skid turn.here is 
> there a link between 400rpm and 400in-lbf to make a full skid turn ?

no

The estimate of 400 in-lbf was based on two observations.

Hetzer #T010 originally had 12V Makita drill motors (320 in-lbf each
with 1:1 drive ratio) and did not have enough torque for skid turns
in tall grass.  I switched to 24V Makita drill motors (476 in-lbf each
with 1:1 drive ratio) and it has plenty of torque.

Secondly, most MAG tanks use EV Warriors at 12V (691 in-oz
with 9:1 drive ratio = 389 in-lbf) and they have plenty of torque.

>By the way is the total weight of the tank is inclueded ? Is it 120 pounds ?

This simple estimate is based on an average size tank that weighs
about 80-120 pounds with about 4 inch diameter sprockets and
about 18 to 24 inch ground contact length.

Torque required for full-skid turns is:
proportional to weight (higher weight requires higher torque)
proportional to ground contact length (longer track requires higher torque)
proportional to diameter of drive sprocket (larger sprocket requires higher 
torque)
proportional to lateral friction of track (higher friction requires higher 
torque)
inversely proportional to track guage (wider separation of tracks requires 
less torque)

>Also a thing i don't get about the specs :
>the spec of the EV warrior are at 12V
>Stall torque : 691 in-oz
>Peak HorsePower : 0.38 hp
>
>The mini EV motor are :
>Stall torque : 64.64 in-oz
>peak ph -at-12v : 0.313 hp
>
>How could the stall torque on one motor be ten times biger than the other 
>motor and
>how peak horse power could be kind of the same.

Stall torque occurs at 0 rpm.  It does not occur
at maximum power.

>An other thing, could we underpower a motor:
>if i try to make working a 24V dewalt motor at only 12v?
>Will it work? if yes how good ?

bad idea

>Also, is it the shortest diameter sprocket wheel where should be connected 
>the motor
>or the longuest sprocket wheels ?

see above

Joe

**********************************************
Joe Sommer, Anvilus Machine Works
2378 Nantucket Circle, State College, PA 16803
814.234.4773     anvilus9-at-adelphia.net
http://www.anvilus.com