Following the thread on electric reverse systems I was pondering the other day on the best way to control one rather than simply putting a switch on
the dash. I've worked out an idea, tell me what you think of this.
The car (BEC) will have a forward-back stickshift on the tunnel. You'd engage reverse by sticking the gearbox in neutral, putting your foot on
the brake pedal then pushing the shift lever to the left. You then activate the reversing motor with the brake pedal - release brake, motor pushes
car back. Push brake, motor cuts out. To get out of reverse you just slide the lever back to the right and you're ready to go.
The stick would normally be locked into the right (forwards) position. The electrical system would unlatch the shifter to allow it to move left and
select reverse only if your foot is on the brake, the gearbox is in neutral and the speedo is registering zero (or close enough). When in the left
position the shifter cannot be pushed forward or back to engage a gear. The latch will be failsafe in that no condition will prevent the gearstick
being moved back to the right, ie you can always get out of reverse.
I guess I like this idea as it controls a bolted-on reverse using pedals and gearstick much like a CEC, which I will appreciate if i use the car as
much as i'm hoping. Also I just like it when things are integrated and seamless, and of course if i'm honest i enjoy an engineering problem
more than i enjoy using the finished item. The mechanical bits are not difficult and don't present too much extra work given that I probably
will fabricate a stickshift anyway, and the electronic bits aren't too tricky. Also I don't think any bits involved would be expensive.
On the other hand of course there's no actual difference in usability when compared to the button-on-the-dash and i'm not confident that
having got to that stage of the build i won't already have cashed in all my willpower. Then there's the obvious question - what would the
SVA man make of it?
What you think? Anyone done simlar? See any problems?
I think it sounds like a great idea, but to my mind a little over-complicated with fail-safes / lockouts. (You can happily try to select reverse in
CECs whilst moving forwards).
I do like the idea of controlling the motor from the brake pedal, that's quite elegant. There is actually a distinct practical advantage here too
- you can keep both hands on the wheel.
I would have a dash switch or button on the tunnel to activate reverse, this would be wired in with the brake switch and neutral light so that the
motor comes on with the switch on, the engine in neutral and the brake pedal up. Any one action out of applying the brake, selecting a gear or
switching off the switch would cease reversing.
This setup is simple, purely electrical and uses components already present on the vehicle except for the master switch and relay.
Don't see how it would be a problem at SVA, they don't check anything to do with reverse gears.
[Edited on 12/3/08 by matt_claydon]
So you can engage the reverse at speed? That is good to know. I was working on the assumption that to do so would be at best expensive and at worst
dangerous.
I like your idea. All you'd need is a push switch and a reverse gear light, then selecting a gear or pushing in the clutch would deselect
reverse. A lot simpler...
I still kind of like the notion of the stickshift selecting reverse though. I'm not sure why, come to think of it. Perhaps because it feels
more like what you'd find on a production car? I'm sure that shouldn't make a difference! I'll think on it, your idea seems a
lot simpler and simple is usually better.
Sounds too complicated to me and something more to go wrong.
I am using a solenoid type starter which will be wired through a toggle switch (off-on-spring). This will also have a relay controlled by the neutral
light for safety.
I will just put the bec in neutral, lift a doomsday cover.
Switching the toggle to the ON position will bring on the reverse light, in the spring position it will engage the solenoid starter.
To stop the car, all I have to do is release the spring position. This means it is quick to stop.
Despite alll the failsafes and protections from putting it in reverse at the wrong time, which are good. You still end up with a system where, unless you are willfully pressing the brake pedal, you have a car that will move or continue to move on it's own. ie the opposite of the accelerator pedal where if you take your foot off you slow down, that does'nt seem right?
quote:
Originally posted by ReMan
Despite alll the failsafes and protections from putting it in reverse at the wrong time, which are good. You still end up with a system where, unless you are willfully pressing the brake pedal, you have a car that will move or continue to move on it's own. ie the opposite of the accelerator pedal where if you take your foot off you slow down, that does'nt seem right?
quote:
Originally posted by ReMan
Despite alll the failsafes and protections from putting it in reverse at the wrong time, which are good. You still end up with a system where, unless you are willfully pressing the brake pedal, you have a car that will move or continue to move on it's own. ie the opposite of the accelerator pedal where if you take your foot off you slow down, that does'nt seem right?
quote:
Originally posted by jlparsons
So you can engage the reverse at speed?
Why not try to mimic a 'real' reverse gear?
Reverse selector sw interlocked with neutral. Clutch up starts motor and throttle position controls the motor speed....
quote:
Originally posted by bartonp
Why not try to mimic a 'real' reverse gear?
Reverse selector sw interlocked with neutral. Clutch up starts motor and throttle position controls the motor speed....
quote:
Originally posted by bartonp
...and throttle position controls the motor speed....
What about trying to engage the reverse with the clutch.
Take a flywheel type thing on the output shaft/diff depending on where you want to put it and then have the motor engaged against the side of the
wheel at 90deg but with it able to pivot off the wheel actuated by the clutch lever. This esentially allows you to slip the clutch to control the
speed.
Just an idea though. No idea if you could get it to work.
Bit like this
You would need a way of making sure the motor slips and also a way of locking the motor away from the flywheel while in normal use
[Edited on 12/3/08 by chunkytfg]
And yes i am fully aware of a lack of ability to draw using MS Paint!!!
Looks like a complicated way of controlling output, and it would be difficult to make it reliable. Rather than go to the effort of effectively
clutching the electric motor you could just divert the output from the throttle sensor to a stepper to vary the power to the motor when in reverse.
But would either be worth it? Being able to trigger reverse with the pedals whilst having both hands on the wheel I think is worth a bit of work, but
to control the output level would be many times the effort and I don't think the benefit would justify it.
You look fit in them pigtails by the way.
quote:
Originally posted by Bob C
I also don't really like the thought that if I let go of everything the car will shoot off backwards.
Well, I think i've decided a couple of things -
First i definitly like the idea of running the motor off the brake pedal. It's going to be a lot safer having two hands on the wheel and equally
imortant it's also easier to look around you 180 degrees without having to have one hand on a switch. The fact the deadman position is with the
power on isn't a bad thing provided the safeguards make sure it can only be activated by a live man, as with an automatic tintop (or even a
manual for that matter). The fact that you have to have your foot covering the brake at all times when reversing is also a good thing for safety.
Second, I think i do like the idea of having reverse engaged by pushing the gearshifter to the left. It feels a more elegant and intuitive solution
than to have a seperate button; it makes sense to have forward and reverse gears selected by the same control and ensures only one can be selected at
a time. Also it'll be harder to engage reverse accidentally as the gearstick will be in a different position from neutral. This reduces to near
zero the posibility of thinking the car is in neutral and taking your foot off the brake, only to find it's actually in reverse and suddenly
you're shooting backwards. Also I like the stickshift idea for the fact that you have both electrical and mechancal safeguards - mechanically
moving the stick left is the only way to put power to the reverse, and because the stick can always be pulled back to the right, no electrical failure
can leave you unable to deselect reverse.
I'm thinking this has to be tried! I'm adding to my (long) list...
[Edited on 12/3/08 by jlparsons]
quote:
Originally posted by matt_claydon
quote:
Originally posted by jlparsons
So you can engage the reverse at speed?
No, but you'd have to be pretty stupid to! Like I said, there's nothing to stop you putting a manual gearbox (or an auto for that matter) into reverse when you are moving forward, and yet people don't do it all the time and mash their 'boxes!
I think just using a spring-loaded toggle has a distinct flaw of having to steer with one hand which this idea overcomes. Doing a tight reverse-park or reverse round a corner with only one hand to steer must be quite awkward?
quote:
Originally posted by nitram38
When was the last time you reversed around a corner?
quote:
Also regarding taking your hand off the wheel, it is regarded as a safe way by driving instructors (in fact the only time) to enable you to turn your head enough to get a clear view behind you.
Keeping both hands on the wheel could compromise your view.
quote:
If your reverse is geared correctly, the car should move very slowly. Applying the foot brake slightly will not harm your starter motor. In fact a free spinning starter uses more current than a loaded one.
The technical reason for this is to do with an extremely low resistance of a starter motor which draws large currents.
When you load a starter motor, there is a back emf created which efectively raises your "resistance" and therefore cuts down on the supply current.
quote:
Originally posted by nitram38
That is why you should not connect a starter without a load. Apart from the thing spinning or lurching (even out of a vise) the rise in current is enough to burn it out.
Regarding the debate about two hands on the wheel when reversing, i think the main point is that as your foot is controlling the brake and the motor by default you're free to do anything you like with your two hands, not necessarily have both on the wheel. The fact that you don't need to have one hand on the wheel and the other on a switch means you are free to turn around and look straight behind you - try doing that with one hand on the dash and the other on the wheel! I tend to leave one hand onthe wheel and put one hand on the passenger seat or the sill to the right, depending on which way I'm turning, then I can see around behind me properly. If I did that in a regular switched electric reverse, I wouldn't be able to turn on the motor to actually move...
argh - my previous post had appeared twice, so I deleted one & both disappeared. A lot of old starters were series wound, & a lot of new ones
are permanent magnet commutator motors, often with an epicyclic reduction gearbox. They have very different behaviors. My issue is that I didn't
want a switch, I wanted to be able to control the speed/torque via a pot. I can see if you just want to switch it, the brake switch is all ready made
(though it's likely to 'chatter' if you're not careful) And I still don't like the fact that it will just set off backwards
if you select reverse....
For a pot, I can't use the throttle or the engine will race. The clutch is in the frame, though it's all counter intuitive... I thought
about pulling the throttle up to control reverse - but I don't like that either - it would be hard to find the brake in a hurry. I guess I need
to think about this while I'm sat in the car......
Bob
[Edited on 12/3/08 by Bob C]
How about something to the effect of:
1: whatever lock out you want to ensure you are in N
2: press or release clutch pedal to engage motor.
For the lock out maybe a electric solenoid to keep you from moving the shifter to the left unless you are in N. Or just a covered switch on the
dash.
This way you only need one switch on the clutch pedal and one safety switch to activate it. Both hands on wheel and you have your right foot primed
on the brake so you can quickly stop quickly. I imagine reverse is a little jerky with electric motors so the ability to bump and stop an inch at a
time might be nice.
Wonder if you could get a slow ramping switch to reduce the instant on effect w/o damaging the starter?
quote:
Originally posted by C10CoryM
How about something to the effect of:
1: whatever lock out you want to ensure you are in N
2: press or release clutch pedal to engage motor.
For the lock out maybe a electric solenoid to keep you from moving the shifter to the left unless you are in N. Or just a covered switch on the dash.
This way you only need one switch on the clutch pedal and one safety switch to activate it. Both hands on wheel and you have your right foot primed on the brake so you can quickly stop quickly. I imagine reverse is a little jerky with electric motors so the ability to bump and stop an inch at a time might be nice.
Wonder if you could get a slow ramping switch to reduce the instant on effect w/o damaging the starter?
quote:
Originally posted by jlparsons
quote:
Originally posted by C10CoryM
How about something to the effect of:
1: whatever lock out you want to ensure you are in N
2: press or release clutch pedal to engage motor.
For the lock out maybe a electric solenoid to keep you from moving the shifter to the left unless you are in N. Or just a covered switch on the dash.
This way you only need one switch on the clutch pedal and one safety switch to activate it. Both hands on wheel and you have your right foot primed on the brake so you can quickly stop quickly. I imagine reverse is a little jerky with electric motors so the ability to bump and stop an inch at a time might be nice.
Wonder if you could get a slow ramping switch to reduce the instant on effect w/o damaging the starter?
I did think about that, but I concluded that if you're going to have to cover a pedal, it's better for it to be the brake. If you're using the clutch to control it you're going to have to cover the brake anyway. On the other hand, using a clutch switch may be easier to control, and given that it'd be so easy and quick to switch between the two it definitly warrants trying in case it's better in use.