Re: High-Low gears [TANKS]

[Grant Mahalek <gmahalek-at-shaw.ca>]

Hi Jon,

You seem to have a good grasp of all things "torque".... Perhaps you can 
offer your comments on my power set-up for my Hetzer.

Equipment:
-two new scooter motors; Unite Motor, Model MY1016, 24VDC, 2750rpm, 15.4amp, 
280watt; 11 tooth #25 drive sprockets
-or two used wheel chair motors with right angle gear drives, 24VDC(no other 
information)
-4 inch dia. rubber drive wheels
-"Tyning Track System"
-fixed road wheels
-12VDC/14.4AH or 24VDC/14.4AH or 12VDC/32AH or 24VDC/32AH, gel cel batteries
-Anvilus proportional relay SSR controller with 12VDC relays and 40Amp 
Crydom SSR's

Objective:
-maximum speed 6 to 10 mph
-all up weight; as light as possible
-do not want to over-amp motors
-do not want to over-volt or over-amp the controller or wiring

I remember a robot/drive-train calculation program/website....but I don't 
remember the website....how is your recall?

Anyone else want to throw in their "two cents...". Much appreciated!

Again, thanks for all your help!


Grant
"unregistered" Northern Barbarian
--- Original Message ----- 
From: "jon s kowitz" <jonskowitz-at-hotmail.com>
To: <tanks-at-rctankcombat.com>
Sent: Thursday, February 03, 2005 8:00 PM
Subject: RE: High-Low gears [TANKS]


>
>  Motor torque does not equal Sprocket torque.  Your transmission will act 
> as a lever, so the EV Warriors in your T-34 (wonderful job on that tank 
> btw) that you've got stalled and smoking are producing thier maximum motor 
> torque.  Because of the 9:1 transmission ratio however, the force being 
> applied ot the tracks by the sprocket is 9x the motor's force.  If your 
> transmission had a 21:1 ratio then you'd be applying 21x that force (and 
> this is the point things start exploding).  Or, that same 
> motor/transmission combo could produce the same torque as the stalled 
> motor at 9:1, only it'd still be turning, using less power and generating 
> less heat.
>
>  I think what we want to do is how to vary the transmission ratios between 
> maximum speed and maximum power in a cost-effective manner, and solving 
> all of the technical challenges that go with it.
>
>>Any decent DC speed controller will use pulse width modulation (PWM) to 
>>control a motors speed.  PWM controls a motors speed by pulsing the 
>>current to the motor at a constant rate (modulation) and varies the pulse 
>>width from 0% to 100%.  At full power the pulses meet and become one long 
>>stream of constant current.  There is no reduction of voltage to the 
>>motor, only a variable reduction of time when current is available to the 
>>motor.  This all happens several thousand times a second so looks very 
>>smooth at the motor end.  The big advantage PWM has over a resistance type 
>>of speed control is that excess voltage is not shaved off and wasted as 
>>heat thus conserving battery power.  As this relates to the question at 
>>hand concerning a multiple ratio transmission.  You should consider that 
>>an electric motor produces its maximum amount of torque at 0 RPM (i.e. 
>>when stalled) and the least amount of torque at it's max RPM.  So in the 
>>example sited (rough terrain, skid steering, etc.) a PWM controlled 
>>electric drivetrain optimized to give you the top speed performance 
>>desired will still have the most available torque at close to stall 
>>conditions (skid steer in tall grass as an example).  At least that's how 
>>I understand it and I'm no expert.
>>
>>Steve Tyng
>>
>
>
>