syringe ballest tanks

[jim smith]

Has any one made a piston type balest tank from a syringe ? I have a small 1/144 scale Gato I would like to R/C and am looking for a balest system that fits a 1 1/8 cylinder.

[salmon]

Re: syringe ballest tanks

http://youtu.be/P8wJK994Zvo

Here is one I did.

[robert f.]

Re: syringe ballest tanks

Raalst has done one, too

[raalst]

Re: syringe ballest tanks

yep. I did two actually.
one driven by a converted standard servo. a m3 thread was fed through the (tapped) main axle of the servo.
one whole rotation of the servo advanced the thread less than a mm. This proved too slow for a dive tank.
the next one was driven by an expensive linear servo (sold by Firgelli.com) with a throw of 5 cm (2 in.)
this one has worked reliably for a few years. and as for it being expensive, I feel it was expensive for
a servo, but cheap for a dive tank.

both were used in my 1/144 trumpeter Kilo.

[Guest]

Re: syringe ballest tanks

Have you got a lathe, or access to one, or know someone who can machine a few basic parts up for you?

If so, piston tanks are fairly straightforward. If not, they're a lot more difficult. Which isn't to say they're impossible to make with handtools, but you will need to be very competent at bench fitting.

Hobby servos tend to rotate at between about 50-100RPM. For a syringe sized tank you would only be using a fairly modest threaded shaft with a smaller pitch, so with a servo you'd be looking at a minute or so to retract the tank, which is ridiculously slow. I would aim for a filling speed of between 10-20 seconds. you can go quicker, but this generally requires larger motors, which can be bulky.

You can get small geared motors on ebay which will run very happily on servo electronics, and if you're happy to tinker with things, you can use the electronic board to power the motor, giving you a very inexpensive and capable proportional dive tank. Generally standard servo electronics will drive a motor up to about 2-3 watts. Some high power servo electronics will drive considerably more than this.

A couple of minus points with syringes, firstly the pistons are often rather large, this means they take up more space than a custom machined item would. Second point is that the seals themselves tend to have quite a bit of compression, more than is actually optimum for our use, which increases the friction somewhat. Neither of these are major issue, but it's definitely worth taking into account.