That solenoid needs ~1.2A as far as I can tell. So it'll put a pretty big load on your batteries. The cells will need to be AA equivalent or bigger. I don't think a AAA-equivalent can cut it.

The pull length of that solenoid is just 1cm. Is that enough? If you need a longer pull, you'll need to lever it up and that will require a larger pull strength.

1cm should be long enough as far as I can tell, will just have to adjust the brakes a bit.

So if I used 8 AA 1.5v batteries to make the 12v that would be fine?

 

I think so. You might also consider a small, sealed lead acid battery (SLA) at 12V, something like this but even smaller would be OK. This would eliminate all those points of contact between cells that can cause the thing to fail.

 

I think so. You might also consider a small, sealed lead acid battery (SLA) at 12V, something like this but even smaller would be OK. This would eliminate all those points of contact between cells that can cause the thing to fail.

Yeah, fair enough that would make sense, thanks. I still need to find somewhere to mount all of this haha. Should be interesting

 

I like the idea of mounting the battery under the seat. The battery is adding weight to the bike and I think this position will have minimal effect on the balance of the bike.

OK. Rear brake only -- No face plants. However, I do worry about the rear tire either locking up and/or skidding when the brake is applied all at once.
Careful adjustment of the brake and the skill of the rider keeping the correct weight on the rear tire will help. But...

This leads me to think that the action of the brake should be proportional rather then just hard on or full off. This means that the transmitter must be proportional and not on/off. Instead of a switch, a spring loaded pot would be needed for proportional control.

The solenoid will need to be PWM driven to get proportional operation. Alternately, maybe, a large model airplane type of servo motor could be used instead of the solenoid.

 

Wouldn´t something like this http://www.parktool.com/blog/repair-help/bmx-freestyle-detangler-adjustment be ultimately cheaper and easier?

 

I like the idea of mounting the battery under the seat. The battery is adding weight to the bike and I think this position will have minimal effect on the balance of the bike.

OK. Rear brake only -- No face plants. However, I do worry about the rear tire either locking up and/or skidding when the brake is applied all at once.
Careful adjustment of the brake and the skill of the rider keeping the correct weight on the rear tire will help. But...

This leads me to think that the action of the brake should be proportional rather then just hard on or full off. This means that the transmitter must be proportional and not on/off. Instead of a switch, a spring loaded pot would be needed for proportional control.

The solenoid will need to be PWM driven to get proportional operation. Alternately, maybe, a large model airplane type of servo motor could be used instead of the solenoid.

Thanks, I understand your point, full on brakes on the rear will inevitably cause the bike to skid, that is a problem. I like the idea of the servo motor also, however I really dont know enough about circuits to actually build something more complex than a simple on/off solenoid. I may try this in future if the skidding really annoys me haha.

 

Wouldn´t something like this http://www.parktool.com/blog/repair-help/bmx-freestyle-detangler-adjustment be ultimately cheaper and easier?

Detanglers are actually very mainstream in BMX; I have had one in fact. But I really don't like how the brake lever gets in the way, so I thought I'd try this little project to see if it could be done.

 

Thanks, I understand your point, full on brakes on the rear will inevitably cause the bike to skid, that is a problem. I like the idea of the servo motor also, however I really dont know enough about circuits to actually build something more complex than a simple on/off solenoid. I may try this in future if the skidding really annoys me haha.

I would recommend an experiment. Try braking by _not_ gently squeezing the brake lever. If you survive this then go ahead and build the brake without proportional control.

 

I would recommend an experiment. Try braking by _not_ gently squeezing the brake lever. If you survive this then go ahead and build the brake without proportional control.

Hahaha I'm trying not to sound like I have an answer for everything ahah, but the proportionality doesn't concern me. If it were a road bike then fair enough but a BMX, when your in the air most of the time, and don't necessarily need brakes (lots of people are brakeless because they aren't as vital as they are in other disciplines of cycling). I have a brake, not because I want to stop, but because pressing the brake in the air adds control and the brakes don't really need to be proportional to get that control in the air. For example, when performing a frontflip, you lock the brake to lock your cranks so you can throw yourself forward without your feet moving.

I'm really sensing I'm being annoying haha. I do like the idea of trying to make proportion brakes though, I may actually try it on my mountain bike at some point. Only problem with that is brakes are a little more important on a mountain bike. Imagine speeding down a hill and realising a wire has snapped or something haha.

 

Annoying? Not to me. I just wanted to drive home how dangerous on/off braking is. Obviously you already knew that.

Braking in the air is _not_ what I was visualizing.

OK, how about this: Stick with a mechanical brake but get rid of the lever. Instead use twisting (rotating) the handle bar grip to apply the brake. Here are some thoughts on that concept:

The direction of the rotation would pull knuckles up and the thumb down to apply the brake.

There would be a ridge under knuckles to "pull" on when braking.

The grip only twists one direction -- toward braking.

A rotating grip might be made by forcing a thin brass tube into a grip. The tube would be just big enough to fit over the handle bar.

A cylinder would attach to the inside end of the grip/tubing. The brake cable wraps around the cylinder.

The cylinder diameter sets sensitivity of braking. Not real critical for your type of braking.

 

Annoying? Not to me. I just wanted to drive home how dangerous on/off braking is. Obviously you already knew that.

Braking in the air is _not_ what I was visualizing.

OK, how about this: Stick with a mechanical brake but get rid of the lever. Instead use twisting (rotating) the handle bar grip to apply the brake. Here are some thoughts on that concept:

The direction of the rotation would pull knuckles up and the thumb down to apply the brake.

There would be a ridge under knuckles to "pull" on when braking.

The grip only twists one direction -- toward braking.

A rotating grip might be made by forcing a thin brass tube into a grip. The tube would be just big enough to fit over the handle bar.

A cylinder would attach to the inside end of the grip/tubing. The brake cable wraps around the cylinder.

The cylinder diameter sets sensitivity of braking. Not real critical for your type of braking.

Hmm I don't know about that, I feel like I'd accidentally brake at times and it would be hard to twist while doing other tricks. I don't really see what's wrong with the solenoid really haha.

 

This is why gyro's were invented http://www.chainreactioncycles.com/...gclid=CMve36j81MECFVGWtAodt2AAZA&gclsrc=aw.ds

 

This is why gyro's were invented http://www.chainreactioncycles.com/...gclid=CMve36j81MECFVGWtAodt2AAZA&gclsrc=aw.ds

Yeaaahh... Read the rest of the thread

 

Hmm I don't know about that, I feel like I'd accidentally brake at times and it would be hard to twist while doing other tricks. I don't really see what's wrong with the solenoid really haha.

Nothing wrong with the solenoid idea. I was just thinking of alternatives. The thinking was prompted by wondering how you would activate the switch.

By the way, how are you intending to push the switch?

Speaking of the switch, if wayneh is right then the switch must be rated for a minimum of 2 amp at 12 volts DC. 5 amps would be better. If you you wnat to use a smaller/cheaper switch then you will want a power MOS-FET to drive the solenoid.

Speaking of the solenoid, you might be able to use an intermittent duty type. Intermittent use requires that the solenoid be on for short intervals with time to cool between uses. This may apply in you case -- on for a few seconds off for several seconds and then off for minutes. The advantage of an intermittent duty solenoid is that it can be smaller and lighter than a continuous duty solenoid.

(I would have replied sooner but I had to go on a (road) bike ride.)

 

Nothing wrong with the solenoid idea. I was just thinking of alternatives. The thinking was prompted by wondering how you would activate the switch.

By the way, how are you intending to push the switch?

Speaking of the switch, if wayneh is right then the switch must be rated for a minimum of 2 amp at 12 volts DC. 5 amps would be better. If you you wnat to use a smaller/cheaper switch then you will want a power MOS-FET to drive the solenoid.

Speaking of the solenoid, you might be able to use an intermittent duty type. Intermittent use requires that the solenoid be on for short intervals with time to cool between uses. This may apply in you case -- on for a few seconds off for several seconds and then off for minutes. The advantage of an intermittent duty solenoid is that it can be smaller and lighter than a continuous duty solenoid.

(I would have replied sooner but I had to go on a (road) bike ride.)

Haha, thanks for that, I'll look into getting one. The RC receiver and transmitter I planned to buy and use comes with a little key fob thing like a car. I guess I could just take the plastic casing off and mount the hole thing next to the grip and use the button on there.

 

My guess is that if you remove the keyfob case there will not be enough left to use. The case not only protects the electronics but also is part of the battery holder. The case may also be integral to the operation of the antenna.

Will you really be able to find and push that small button while flying through the air? It seems to me that a larger button is in order...