Hmm that is a pretty small force I think.
So basically any solenoid would do right?

 

How did you arrive at the 20Nm in the OP?
Max.

 

I used a torque wrench on the tip of the leaver. And the leaver would move when the wrench reached about 20Nm

 

Yes I re-checked my numbers and looks like I used divide in place of multiply.
So if you had 6cm lever and the scale were to read 16Kg to get it move the lever that would = 9N-m (6.63 Lb-ft) in my revised amount.
Max.

 

For a rough example, solenoid in hand, 6.5 X 5 X 4 cm, 25 ohm driven by cap. discharge, 65,000 uF @ 30 V, gives about 20 lb. Needs less C & more V; maybe 30,ooo uF @ 60V- 90 V. C's used 2 each, 7.5 X 11 cm @ 40V. If used with spring return, would need almost 2 X force.
What is maximum time to operate? Linear actuator around 1 sec. An example: ( not quite linear), 12V DC, 21 RPM, 48 in- lb., gear reduced motor, 6.5" X 3.15" X 3.5", with 1 in crank arm from old catalog.

 

I think you would do better to look at a stepping motor turning a lead-screw, or a reversible dc motor driving a lead-screw...

 

Bernard, I need one that is max 24VDC. Mike can you give me a ling to one of these motors? Are they fast? I need a fast one since I will use it to change gears in my kart (0.2 - 0.3 sec)

 

.... Mike can you give me a ling to one of these motors? Are they fast? I need a fast one since I will use it to change gears in my kart (0.2 - 0.3 sec)

This is a very important specification that you should have stated way back in post #1. With this in mind, I now recommend using a bi-directional pneumatic or hydraulic cylinder, controlled by a solenoid valve.

 

This is a very important specification that you should have stated way back in post #1. With this in mind, I now recommend using a bi-directional pneumatic or hydraulic cylinder, controlled by a solenoid valve.

The thing is that the pneumatic and hydraulic cylinders have to be actuated by some sort of pump/compressor right? I don't have the space to put that on my kart.

 

Would a starter solenoid be the trick here?

 

Would a starter solenoid be the trick here?

Starter solenoids (the big one attached to the side of an automotive starter motor that push the drive gear into the ring gear) have more than enough force, but their throw is too short, and besides, they take a huge amount of current. If the OP doesn't have room for a vacuum or pressure pump, he likely doesn't have room for a large automotive battery, either...

 

Would a starter solenoid be the trick here?

No room for a car battery. At most i can use a scooter battery.

 

Making some assumptions here, I am guessing that the gear change solenoid would be activated by manual intervention? IOW not automatically?
Is the reason for the electrical solution to avoid mechanical linkage?
If so, one possible solution would be an adaptation of automotive hydraulic brake type system, where you could operate a foot or hand pedal to transfer to a short stroke cylinder on the moment arm of the G.C.
Max.

 

"I am guessing that the gear change solenoid would be activated by manual intervention?" - that is correct. With a couple of pedals behind the steering wheel.
Could you explain a little bit the hydraulic brake idea please?

 

If you have access to a Autowrecker you might salvage a master cylinder and foot pedal to use as the input, the output cylinder probably does not have to be as large as a disc brake cyclinder so you could source a stubby short stroke hyd cylinder of some kind, there should be a few on ebay etc.
Coupling the input and output cycl could be done with flex rubber type tube with suitable rating.
It may need spring return and you could also adjust the attachment point of the shift lever to give the appropriate stroke/power etc.
Some experimentation may be needed!
Max.

 

Interesting idea. Thank you.
So just to be clear, there are no electric solenoids that meet my criteria?

 

You may find one or even wind your own, but I suspect as others have mentioned, the power required may be too much for the smaller battery, especially with the frequency of operation.
Max.

 

For a shifter don't you need it to go both directions, for up and down shifting? Here is a link to a pretty powerful RC servo that would probably do it; http://www.pololu.com/product/2147/specs

For a hydraulic system like Max was suggesting, I'd use a hydraulic clutch cylinder from a car or pickup truck. Is there a reason you can't use control cables? Like brake cables in a bicycle or motorcycle clutch cable.

 

In my opinion, a solenoid is not a good choice for your shifter application. The force is high, solenoids are not very efficient, you would need a monster solenoid and lot's of power to waste.
The servo idea is much more elegant, and the motion will smoother and easier on the mechanics of the gearbox as well. Shifting gears with solenoid is the electro-mechanical equivalent of shifting gears with a hammer, the armature needs to be a heavy piece of metal for magnetic purposes, which means it's got a lot of inertia.