[DeTomaso] More cruise control issues

[Tomas Gunnarsson]

The pulse frequency at a given speed is about ten times higher if you use the coil signal vs using a single magnet on one of the driveshafts. This might cause a problem if the controller is not set up for it. I had problems when using a bicycle computer to monitor speed on a gokart wheeled vehicle. While the speedo was well capable of indicating the top speed of the vehicle the indicated speed dropped to half of the real speed when we hit about 40 km/h. On a normal size bicycle wheel that pulse frequency would correspond to freeway speeds. The problem was not the capacity of the computer itself but the sensor/input stage circuitry.

Tomas

----- Original Message ----- 
From: "Thomas Tornblom" <Thomas.Tornblom at hax.se>
To: "Charles McCall" <charlesmccall at gmail.com>
Cc: <asajay at asajay.com>; <detomaso at realbig.com>
Sent: Monday, August 31, 2009 8:10 PM
Subject: Re: [DeTomaso] More cruise control issues


> Charles McCall skrev:
>> On Mon, Aug 31, 2009 at 7:26 PM, <asajay at asajay.com> wrote:
>> 
>>> -That- brought back memories.
>>>
>>> I used an old CompuCruise computer in an older car of mine that had a
>>> manual transmission.  The Tach signal was only -one- source of input
>>> for the cruise control.  The others were the brake switch and the
>>> third was a set of magnets attached to the drive line and picked up by
>>> a nearby sensor.  -That- was the speed sensor.
>>>
>>> The tach adapter can NOT be used as a speed sensor.  After all, you'll
>>> get the same rpm in 1st gear, second gear, third, etc.  i.e. 2,000 rpm
>>> in first is one speed, while 2,000 rpm in 5th is totally different.
>>> You -can't- use the tach as a speed sensor.
>>>
>> *****Why not? The message you are sending to the cc brain is not "maintain
>> 47 mph"... the message you are sending is "maintain the current speed,
>> whatever it may be". If you are in 3rd at 3000 rpm, it will maintain a
>> constant 30mph (for example). If you are in 5th at 3000 rpm it will maintain
>> a constant 70mph. If you press the clutch to change gears, all bets are off
>> and it shuts off.
> 
> One reason for tapping into the trans instead of engine rpm is to make 
> sure speed is constant in case you hit "resume" in a different gear. Say 
> you set the speed in 4:th, then up shift to 5:th and hit "resume", that 
> might produce a surprise :-)
> 
> 
> Thomas
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