Jump to content

Over Drive Logic revisited


Recommended Posts

Hi Folks.

a couple of years back I made a nice little OD logic box. It had a couple of big(ish) relays and a large capacitor to make things work.

And it did work. It did everything that you would want. It cost about £10 in parts but i took a fair bit of R&D to make everything do what it should.

 

The difficult thing with these boxes is the switch. It needs to be a momentary switch with a long stalk - not common.

The normal toggle switch, because of the long stalk, has quite a throw on it

I eventually made a rigid stalk with a push button switch on the end - see the first pic

And yes, the stalk is Stainless steel from the Concorde - what else would do.

A problem with this assembly  is that if/when I needed to remove/renew the switch I had to disassemble the whole thing which was tedious.

So I have recently made a switch mechanism with the switch screwed into the base of the stalk. The rigid tube is silver soldered to the brass end fitting with the switch

See the 2nd & 3rd pics

I'm quite proud of the circuit for the on/off as it uses the same button (my secret)

To operate it you simply touch it with a finger without taking your hand off the wheel.

I then had a look at the box of tricks it self. I have been having trouble with the indicator LED. Others that have this box have not reported an issue here.

Anyway, I removed the PNP transistor that powered the LED and fitted a small relay. This is powered by the dash lights. There is a dimmer control for this LED

Pic 4 shows the innards tightly crammed into position

Another area I tidied up was the wires that come out of the box. I found a nice 7 pin DIN plug and socket that works well. The combination is lockable so it will not drop out when running. see pic 5

I've been using Vero strip board to hold the circuit but it requires more links and holes in the board. So I have been playing at making a dedicated PCB.

Now most people use some sort of etchant to make the fancy copper track, or if you are smart you send off the art work and get somebody to make the PCB's for you.

I decided to use a full blown milling machine (it has an X/Y bed) and a special pointed cutting. These are tapered cutters that you can grind down to give any size of cut between the tracks (handy for getting around IC pins) 

My first assembled board didn't work - this upset me somewhat as it should have work. When I examined the copper tracks I found a small whisker of solder shorting out two tracks.    

So all in all I now have a much neater box (with the DIN plug/socket) an improved PCB / lay out. And the on/off button is easier to work with.

I'm sure this electrickery will be lost on many of you but it keeps me busy.

 

Roger

 

 

 

 

P1070049a.jpg

P1070093a.jpg

P1070094a.jpg

P1070098a.jpg

P1070095a.jpg

Edited by RogerH
Link to post
Share on other sites

I envy your engineering skills Roger. My OD Logic box keeps the toggle switch so no skill on my part was required.

Cheers, Richard

PS: I did do an engineering course as part of my apprenticeship at Bracknell college back in 1984. Lathe work, milling, gas welding, etc. But these never got used in my electronics career.

Link to post
Share on other sites

Just the sort of inspiring work we expect from you, Damn you Hogarth ! (very well done).

Miuck Richards

Link to post
Share on other sites

Can't pretend I understand the need for such a device never mind design one from scratch but I love the fact it cost £10.

Roger your just full of surprises obviously too much time on your hands!

Andy

Link to post
Share on other sites
On 3/20/2021 at 7:53 PM, PodOne said:

Can't pretend I understand the need for such a device never mind design one from scratch but I love the fact it cost £10.

Roger your just full of surprises obviously too much time on your hands!

Andy

Wouldnt be without mine and Ive fitted a fair few as well.

Stuart.

Link to post
Share on other sites

I agree with Stuart. 

The Logic box makes the overdrive work the way it ought. 

It avoids those awkward moments when one stops the car, forgets to flip the usual switch to OFF, then starts motoring and, on selecting 2nd gear, the engine bogs down because overdrive has been engaged!

And no more fiddling to disengage overdrive when shifting from o/d 2nd to 3rd, and from o/d 3rd to top as the Logic box automatically disengages o/d when the lever is moved.

I installed a Revington unit in 2004, with a switch similar to that installed in 1962 by the Works for the headlamp flasher, and wouldn't be without it.

Ian Cornish

Link to post
Share on other sites

I am in awe of Roger being able to make his own and at a great price too. Those switches are fantastic.it’s all so tidy.

like Ian I have the revington version ( I had it fitted by an auto electrician- I don’t understand electrickery) with my own led warning light and momentary toggle switch on the dash I can reach with hand on the wheel. 
it’s great to change od with foot to the floor acceleration.

 

Link to post
Share on other sites
32 minutes ago, Hamish said:

it’s great to change od with foot to the floor acceleration.

 

Thats how you should change up into and down out of overdrive anyway.

Stuart.

Link to post
Share on other sites

Absolutely, Stuart - the only way to avoid damage to the transmission system, engine mountings etc. is to have power on whilst changing into or out of overdrive.

Full power when engaging overdrive, just a touch on the accelerator when disengaging.

Ian Cornish

Link to post
Share on other sites
21 minutes ago, ianc said:

, just a touch on the accelerator when disengaging.

Ian Cornish

Depends on how fast you come upon the need to change down;)

Stuart.

Link to post
Share on other sites
2 hours ago, Hamish said:

I am in awe of Roger being able to make his own and at a great price too. Those switches are fantastic.it’s all so tidy.

like Ian I have the revington version ( I had it fitted by an auto electrician- I don’t understand electrickery) with my own led warning light and momentary toggle switch on the dash I can reach with hand on the wheel. 
it’s great to change od with foot to the floor acceleration.

 

 Hamish the parts for my latest version are a bit more expensive  as I've added a few more bit to it.

 

Roger

Edited by RogerH
Link to post
Share on other sites

After a bit more understanding and explanation from you all it seems the logic box is a worth while upgrade so I might as well factor it into my rebuild. So who sells the best fit and forget option for a 1969 PI with A Type OD? 

Thanks

Andy

Link to post
Share on other sites

Not to attempt to steal any thunder from Roger even were that possible, but rather to show there is more than one way to do it cheaply - total cost about £10 -  this is the arrangement I have used. I wanted to have a centre-sprung lever switch which is flicked down to turn the OD on and flicked up to turn it off again, as well as having the usual logic switching. The logic circuit is very simple and uses two changeover relays.

 

The switch is a centre-off momentary SPDT toggle which I have modified  by lengthening the operating lever to allow fingertip operation.

odsw.jpg.d602685811455cf1456949eec455a118.jpg

 

This is the schematic for the logic circuit:

1989625237_ODlogic.jpg.6f537fbef57471f760a11ae19d6f7684.jpg

and the relays are fitted up beside the pedal box

odrelay.jpg.e4b490e1a64be3b0abbb53bf2e8864cb.jpg

Edited by RobH
Link to post
Share on other sites

I fit the Revington ones, not cheap but neat and fit out of the way, for a switch if you want to fit one to the dash instead of the gear stick then these work well. Switch

Stuart.

Link to post
Share on other sites

I bought one on Ebay years ago.  I paid £12.50 plus postage.  I don't know if it is the same type as the Revington ones.  It's basically a small rectangular black box about 3" x 2" by about 1/2" thick.  It knocks the overdrive out whenever I change gear and I have to flick the overdrive switch off and on to re-engage it.  It has a small indicator light that shows when it has activated.  Touch wood, to date it has been very effective.

Rgds Ian

Link to post
Share on other sites

I also have a Revington one but altered my switch by filling in the notch that holds it in the on position by filling in with a small section of alloy held in with epoxy glue then using a small spring out of a toggle switch fitted to give it the return movement been working well for over ten years now and looks standard.

Keith

Link to post
Share on other sites

Mine uses a thyristor to latch the overdrive on until you pass through neutral and the thyristor turns off.  No moving parts.  Not as fully functional as some but it avoids accidentally bogging down.

Edited by peejay4A
Link to post
Share on other sites
3 hours ago, Ian Vincent said:

I bought one on Ebay years ago.  I paid £12.50 plus postage.  I don't know if it is the same type as the Revington ones.  It's basically a small rectangular black box about 3" x 2" by about 1/2" thick.  It knocks the overdrive out whenever I change gear and I have to flick the overdrive switch off and on to re-engage it.  It has a small indicator light that shows when it has activated.  Touch wood, to date it has been very effective.

Rgds Ian

That's probably the one that was made by Tim Walker a former TRR member, sadly no longer with us now. Works really well.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...

Important Information

Please familiarise yourself with our Terms and Conditions. By using this site, you agree to the following: Terms of Use.