Search all of my sites with Google

Saturday, September 12, 2009

Shock The Coolant

On the Endless Sphere forums, in a thread regarding hub motor cooling, someone proposed a very interesting idea:

jsplifer said: "Basically you modify the suspension to pump a fluid through one way valves in order for the fluid to make a loop through the motor, and through a heat sink/radiator mounted somewhere."
There's a link to his sketch of the idea in that thread.

It made me start thinking, and in a moment I had a more complex but improved idea for essentially the same thing. Below is essentially the post I made there, preserved here on the blog too, in case I need to find the idea later:

Rather than modifying the shock directly, use a lever and/or gear system to take the very small linear movement of the shock, and convert it into a long linear throw for pumping much more volume, using an external little pump. That way you could just bolt it on any bike, rather than modifying a specific shock fork (the modifications of which would be different for each one, too).

All it would need is to connect between the crown and the U below that where the screw mount is often unused (when they come equipped with linear pull or other types of brakes using the studs).

The compression between those points could act across a lever, or could have teeth on a straight strip that engage a rotating gear, which (if necessary) in turn engages a different sized gear to give the ratio needed for high speed pump movement.

Also, one-way valves would be unnecessary, just use a ratcheting gear (freewheel) so it only goes one way, and connect that gear to a regular little motorized fluid pump, just not using any power on the motor--driving the shaft from outside, instead. This way if you really needed to, because of being on a really smooth road, you could still power the pump to cool things.

It's more complicated, but would be even more efficient, as much more coolant could be moved thru the system in much less time.

The same system could be used on the rear shock for a rear-mounted hub motor (which could probably not be done, at least not easily, with the original method).

It is even possible to tie both ends together to make a larger circulation system (but it would get heavier quick due to more fluid in the system).

This system could be used to cool controllers and/or battery packs as well as motors.

I have some stuff laying around somewhere that could be adapted to test this, to try cooling my wheelchair motor without using an electric pump, using some parts off a PC liquid cooling system.

Additionally, though it would not generate a lot of power, using a small motor in place of the pump in that same setup would generate some electricity, more on bumpy roads than others, and depending on how sturdily the system was built, would even provide some damping of the shock system (but slowing it's response, so shocks would not be absorbed quite as well, if the motor/generator was under too high a load). It could possibly generate enough power to run small LED lights, at least, on a rough enough road. :)


  1. I might have missed the results of trying out the idea of attaching heatsinks to the outside of the motor. Since the bike is moving, air cooling could do pretty well.

  2. Here is a servo motor that I am considering.

  3. I haven't tried the heatsinks yet. Wish I had, because I needed them yesterday. :(

    If I do the heatsinks, I think I may just go with a similar method to Naeem's on Endless Sphere, where he has folded a strip of metal into fins and a circular ring, and slipped it over the motor. I'd just add tabs to the ring part, and clamp it down with radiator hose clamps, with thermal paste between the ring and the motor.

  4. Re: the servo motor, there's no specs on the ebay page, so I can't tell if it's a good one for you or not. Some servo motors are rated high enough that they could do continuous duty as ebike motors, but some are not made for continuous work, and need cooling time, or need to be run at much less than max ratings.

    Also, I couldn't tell if that was a plain DC servo motor, or if it was a stepper-type servo motor. If the latter, you'd have to either rewire it, or adapt a brushless controller type of design to work it.


Alternate suggestions or improvements to anything that's been posted is very welcome, and extreme detail is preferred to brevity.

Keep in mind that unless you leave an email address in your comment, I haven't any way to reply to you except to reply to your comment here. That means if you want a reply, you'll have to come back to *this* blog entry and it's comments to see my reply to you, unless you leave some method of contact within your comment.