Re: [mowbot] batteries

William J. O'Reilly III (pookie nospam at
Sat, 26 Oct 1996 02:50:08 -0500

At 01:57 AM 10/26/96 +0100, you wrote:
>DON AUTRY <Don.L.Autry nospam at> wrote:
>> What does stall amps on a motor mean, it this the amount of
>> current it takes to get the motor started?
>It's the current the motor takes just at the point where the load is
>too much for it and it stops turning. You need to design drive circuits
>to cope with stall current just in case your robot runs in to a wall,
>but with effective power cut-outs (tachos, touch bars) it won't be
>necessary to cope with such a high current for very long. For that
>reason most motors specs quote stall current.
>It's harder to get figures for starying current because it is less than
>the stall current so doesn't affect the design much. There aren't many
>motors in RS that do list starting current; those that do seem to quote
>from 2 to 3 times the normal operating current.
>Although I've had my ideas on motors scaled up a bit since my early posts,
>I still remain to be convinced that we need to budget more than 1A per
>motor even under difficult conditions. But to experiment is to know,
>so sooner or later someone is going to have to buy some motors and try
>a mock-up.

I've been into the RC cars that have been spoken of. Here's the trick with
them--They overheat, they torque out, they are energy wasters...unless you
run them slow. I had a car that, with 5cm wheels would go up to 20
meters/sec on pavement. It only ran for about 2 minutes, using 6 NiCd
batteries...but that was a lot of torque are very high rpm. And the
wheels...they are a smooshy rubber, designed for wet grass/mud/dirt. Could
be applicable here.

I have 2 motors. One is a light duty and one a heavy duty.

One other thing about the can buy nylon gears for step downs and
a differential.

William O'Reilly
pookie nospam at