Re: [CAD_CAM_EDM_DRO] Re: [DIY-CNC] need transmission ideas / advice re: gantry

A 12VDC starter motor is a terrible idea. It's powerful for short
bursts. It will quickly overheat in any other duty, so it's actually
quite a weak motor for continuous duty. Even if you run it at low
power, it has no means of cooling itself so the heat will build up.
It's also inefficient.

You may be underestimating you load requirements.
Your lift requires a total energy of 11,760 watt-seconds, or 15.76
hp-seconds. One hp motor out takes 15.76sec to lift. 2.5hp needs
6.3sec. That does not include the kinetic energy required, which can be
very significant as higher speeds are used. The kinetic energy goes up
with the square of the velocity used.

The treadmill motor is probably an ideal, economic yet effective load.
How are you getting the 12v to power the 130VDC motor? An inverter?

The 200ah batts- or the cables connecting them, or the inverter- may be
"bogging down" and dropping voltage under this sort of load, which kills
motor torque. But it's not the motor's fault. If the batts were both
under a 1C discharge- which is a lot of load for lead acid, in good
condition, and they can only handle this sort of thing intermittently-
then put through a 120v inverter and motor- then it'd be able to lift in
about 4sec, but that's nearly "flooring" the batteries.

How fast were you expecting to move this load?

Danny

Bob Muse wrote:

> Get a 12VDC winch or possibly a 12VDC starter motor with gear reduction.
> This type of series wound DC motor will produce a lot of torque at low rpm.
> Will also require a lot of current-should work fine with your battery.
> ----- Original Message -----
> From: "gcode fi (hanermo)" <yahoog@...>
> To: <CAD_CAM_EDM_DRO@yahoogroups.com>
> Sent: Monday, May 11, 2009 11:55 AM
> Subject: [CAD_CAM_EDM_DRO] Re: [DIY-CNC] need transmission ideas / advice
> re: gantry
>
>
>
>> I am making a large cnc-driven gantry, which is done.(4.4 m wide, 4 m
>> lift, 8 m rails).
>> At the last moment, I ran into some difficulties at the transmission;
>> 2-stage, HTD 5 mm 15 mm wide steel pulleys and timing belts, 1:3 to 1:3
>>
> for 1:9 total.
>
>> I have no way to get electricity to the site, we run from 2 large
>> batteries of 12 V DC (200 amp hours each).
>>
>> I am using a DC treadmill motor, from surplus center, rated upto 2.5 HP
>> and 130 V DC.
>> Unfortunately, the motor seems to be too weak on torque !
>>
>> Any ideas on how to move the gantry ?
>>
>> The gantry and payload are 300 kg in mass, its a rolling non-dragging
>> application, up a steep gradient of 45 degrees, 8 m length, total lift 4
>>
> m.