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monster garage ...wheelchair Idea
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Posted by: sbates

07/02/2003, 00:00:48

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Okay everyone, you've all watched it, now it's our turn, we're building an electric wheelchair, driven by a 12v starter motor out of a toyota 3t engine( gear reduced, and stronger than a chevy 350 starter), we need help with the pulleys ( setup)... We tried  a 2" on the starter and a 2" on the axle..result .. speed but no torque.... tried a 2" on the starter and 6" on axle speed an very little torque...rpms on the starter with 1/2 shaft 200/250, 675 amps power... Any ideas????? 






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Dragster wheelchair
Re: monster garage ...wheelchair -- sbates Post Reply Top of thread Forum
Posted by: Cragyon
Bart
07/02/2003, 09:07:16

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I'm still struggling with the visual image of a a realy fast wheelchair for grandma.

The torque created by the starter motor must be at least 150 + ft-lbs.  I didn't see any formulae on Engineers Edge that would help with the calculations, (hint hint).  How much torque do you need?  I believe the math is a simple ratio equation such as:

 

RPM * torque = RPM1*torque1

 

 







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Re: Dragster wheelchair
Re: Dragster wheelchair -- Cragyon Post Reply Top of thread Forum
Posted by: sbates

07/02/2003, 10:12:58

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based on what we've done so far the wheel chair will not move at this point, and we need to be able to push a 200# man.






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Re: Dragster wheelchair
Re: Re: Dragster wheelchair -- sbates Post Reply Top of thread Forum
Posted by: Cragyon
Bart
07/02/2003, 11:12:42

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For starters (no joke intended) you need to determine how much torque is required to move grandmas chair while 200# is sitting in it.  If you put a torque wrench on the axle and measure somehow, you will have something to base calculations on.  Next, detemine the actual torque of the motor and the wheel diameter.  With this information, a simple estimation of the ratios, etc.  can be made.






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Re: monster garage ...wheelchair
Re: monster garage ...wheelchair -- sbates Post Reply Top of thread Forum
Posted by: prop154

07/02/2003, 06:53:35

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look at using a variable speed drive pulley (if room permits) similiar to what most lawn tractors use.






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monster
Re: monster garage ...wheelchair -- sbates Post Reply Top of thread Forum
Posted by: RKimball

07/02/2003, 01:03:43

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Speed should not be a problem. Torgue on a starter motor is directly porp to current. Are your wires and connect good and heavy? Dropping the ratio to 10 and 1 should still give you plenty of speed.. geeeze .. and up the torgue... but I'm thinking (you havent given many facts) the current is the kicker... A starter motor will deliver whatever current/torque you can get to it... to the point you even burn it to a crisp... In other words if it doesn't deliver speed and has enough current and wire size given, it will melt itself at rotor lock. ...current IS magnetic energy ... IS torque. ... all directly prop.
-randy-
please report back for us



** The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, don't fail to listen to suggestions. -randy-


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Re: monster
Re: monster -- RKimball Post Reply Top of thread Forum
Posted by: sbates

07/02/2003, 08:47:17

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were using about a 6 gauge wire 3/16" dia. bolted directly to ground and switch the current as you speak of is 12volt, 675 amps.  






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real monster more
Re: monster -- RKimball Post Reply Top of thread Forum
Posted by: RKimball

07/02/2003, 01:11:58

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... given that doesn't do it for you... stack two batteries in series and push the current in with twice the punch, 24 VDC, just don't lock the rotor, keep that armature turning.. ..geeeze.. (twice the volts / same resistance = twice the current) = twice the magnetic force... twice the ... I'm getting out of your way.

If your wires are getting hot, they are the problem (more or less). If you go to 24V then run the sel coil on one battery. Be sure your sel contacts are not limiting your current... 24V should get you where you want to be. ...for a little while.. for long enough.
..big wires, two batteries in series, huge contacts = wow!
..just as long as you aren't trying to sell this thing to the public...wink. .. and don't over rev that motor! .. load it (give it work to do) before you punch it with 24V or you could explode the windings.... like not on the bench, .. dauh.
-randy-




** The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, don't fail to listen to suggestions. -randy-

Modified by RKimball at Wed, Jul 02, 2003, 01:33:53

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Re: real monster more
Re: real monster more -- RKimball Post Reply Top of thread Forum
Posted by: sbates

07/02/2003, 08:52:37

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you spoke of 10 :1 ratio, woud that be like the following: 1"dia pulley on the motor to 10" on the axle or visa versa?






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more, real monster more
Re: Re: real monster more -- sbates Post Reply Top of thread Forum
Posted by: RKimball

07/02/2003, 21:23:29

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giggle... NO!!! a 3/16 dia cable simply WILL NOT DO...

You need a serious cable... I don't have my chart, so to make a reasonable guess I'd go with 5/16 or even 3/8 dia. Let's move some electrons. If you want to move many cars out of a ball park quickly you provide many lanes of exit. If you want to provide many amps of current to a starter motor quickly you provide many mills of cable. Remember, current(amps) equal magnetic energy, equals torque! ...wink... no 3/16 will not do... G-luck! That starter likely has a coil made of 1/8 thick my 3/8 or even 5/8 flat copper, ... it is intended to move some serious current. And the slower it turns the more current it will draw. ... so it will provide a lesser torque curve as speed increases and the load gets moving.

Now remember too, if your connections are poor it is like pinching your hose in the front yard, you aren't going to get much current out. YOU MUST HAVE big GOOD CONNECTIONS, ... good ones.

Equally important are the size of the contacts that make the connection when the switch is thrown.. I hope you are using a Ford type starter solenoid to make the contact!! they are cheap and effective for large current 12 volt situations.

later -randy-




** The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, don't fail to listen to suggestions. -randy-

Modified by RKimball at Wed, Jul 02, 2003, 21:31:18

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