Sprocket and Aluminium Track

Hi all,

I am trying to develop a motorised carriage that will sit in some sort of horizontally-mountable perforated metal track (aluminium channel?), whereby the wheels of my motorised carriage are sprockets, and the teeth of the sprockets are aligned to the perforations in the metal channel. The idea roughly is that I’ll have a sprocket as a wheel attached to a stepper motor on my RPi, which will then propel the carriage back and forth down this track.

Where do I find such a combination please?

Thanks so much,

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Sounds interesting, what it is the movable cart going to do?

I have a VERY similar system that I use as a time-lapse camera dolly.
Cart that takes the camera and raspberry pi and has a DC Geared Encoder motor.:

I use 3D printed gearboxes for the drive as well as 3D printed ‘track’ for the gears to drive in.
The rails that it slides down are 25.4mm square section aluminium held in place with 3D printed parts.

So, my 2c worth.
If you want the cart to slide along a perforated channel, you’ll need to get that waterjet or laser cut to be specific for your sprockets.
Rolling on sprockets produced a bumpy ride, it wont be smooth.

I moved away from steppers as they are heavy and power hungry.

Sounds like an interesting project though.


Thanks so much @AndrewBG. Wow, that looks so impressive. Clearly you know what you’re doing from a 3D printing and cutting perspective! Well done.

Our project is also for photography purposes. The idea being that a small RPi camera mounted on some sort of carriage can transverse up and down a horizontal track. It is to reside in a greenhouse, thus our thinking was to have some form of perforated aluminium as a track such that dirt and water have nowhere to sit and potentially interfere with the carriage.

I totally get your point about potentially being a ‘bumpy ride’. Hmmmmm. :thinking: I don’t believe such a thing exists, but it’s almost like a ‘rigid tank track’ that I was roughly thinking of. Ideally, I didn’t really want to use wheels.

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OK so your primary concern was dirt getting in the tracks or wheels?
So for that same reason, I went with a friction surface design.

I was using bearings and round tubes, but the slightest piece of dirt would crunch the tube and leave a little divot.

What if you had rodls like mine to slide on and use a belt drive for locomotive power?


Hi Kirk. Google “rack and pinion” and you will get nearly 20 million hits. I haven’t looked in detail but there seems to be a wealth of information here.

If you are worries about dirt etc have your carriage sit on some sort of rail system and have the rack on top, that is upside down.
Cheers Bob
Edit. Or side on.


I love your tech. drawings @AndrewBG. Well done.

Only slight issue I’d have with a belt drive is the distance I might need to cover. Some greenhouses are quite long.

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Thanks Bob. That was of great help. I guess I wasn’t sure of the terminology to use in a search, so when I was searching things like ‘sprockets’ and ‘rails’, I wasn’t really finding what I was hoping to.

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You’re only limited by the length of belting that you can afford to buy, really. There’s steel belted belts that have practically no stretch.

If you can share a bit more about your use case, it might be easier to come up with a solution.


Thanks @AndrewBG.

I want to be able to film / take photos in a commercial greenhouse. Some of these can be say 30m to 50m long. The idea sort of is (haven’t quite got the whole concept sorted out just yet) that we have some carriage that moves along a dedicated track (say about 40m long). It simply goes back and forth on that track maybe 3 times a day. This track will get wet, and may get dirt on it, though if I invert it (like the rack and pinion Bob was referring to), then there’s little possibility of that happening.

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Hi Kirk
You may get a few ideas if you can find out how the TV cameras are run up and down the sideline at a sporting event. It could be as simple as tracks made from PVC pipe with the camera dolly sitting on it with wheels. They have the man powered cameras too. Also the overhead one is interesting, hanging from 4 cables that ate wound in and out to position the camera anywhere over the field.
Cheers Bob

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Cool, that is what I was thinking you wanted to do :slight_smile:
How high off the ground?

40m is long, that will limit your track and propulsion method.
If you used the aluminium extrusion that I use (25.4mm square) you can probably get that in 6m lengths, meaning about 7 lengths. I use 3m lengths but only because I can get it from bunnings.
Your biggest issue with long tracks is the join and not getting a bump.
I wouldnt go with PVC piping as the track as it will sag without a serious amount of support, however round metal pipe would do just as well as the square that I used.
I went with square as it was easier to mount and get the whole lot flat as you havea continuous flat face to drill the mount holes.
In previous versions I used round pipe and found it difficult over even the 1.2m track that I was using to get the mount holes aligned as the pipe can spin around when drilling.

You need to think about how you’re going to mount it, but I’d say a track config like mine, but hung upside down.

You wont need to have the third rail if you are able to hang the track at regular intervals from the roof trusses, or even fit directly to them.

Rack and pinion motion is going to be an expensive option for 40m unless you can 3D print like my ones, but that will a lot of printing, although they print pretty fast. ie I printed enough for 4m of track in a day, so it would take you a couple of weeks.

Here is the stl if you want it, I have a lot of various gears that mate with this track too.
track.stl.zip (551.5 KB)

Track will work, as would a belt, but the belt tension over 40m is going to be tough.
I can tell you from experience that it’s difficult to not break the 3D printed gearboxes when using a long belt drive due to the forces that the tension applies to the drive gears.

However, probably the best option for such a long dolly track would be to use paracord and wrap it a couple of times around a drum in the dolly cart.
It will make its own tension, as long as the paracord is reasonably without slack in it, as long as you are always travelling in the same direction. Changes in direction will always provide large backlash in a belt/paracord based locomotive solution, but this might not be an issue for you.

Note the other issues that you will need to solve are to do with power and waterproofing.

  1. 40m is a LONG dolly track to sling a power cable.
    I think that if you slung a catenary cable above or to the side of the dolly track and concertina’d it on loops, then it would just drag it along with it. You dont want the cable to be able to snag on anything.

  2. How do you plan to waterproof the raspberry pi? It is really going to need to be sealed up otherwise moisture will definitely get in. You would probably want to look at sealing the Pi with a paint on coating as well.

The last question is how fast do intend it to travel?
Is if for video, stills to check up on growth etc, or for time-lapse purposes?
Those questions will affect the motor/gearbox/control combination and options that you choose.

Oh one more idea, dont forget to include limit switches at either end, the last thing that you want is the cart to crash into an end and try and drive itself off a stop.
You can do limits in a variety of ways, but you will either have the limit at either end of the track and cut power if it hits it (downlise is that you cant start it again and it would cut the power to the Pi) or you would have the limits on either end of the cart and wire them up to the Pi to a GPIO and use the input to stop the Pi locomotion.
The benefit to having them on the cart is that your wires are short and the action is right at the Pi so easy to make sure that you are preventing a crash.

I think that is my brain dump for now, but happy to answer anything that will arise.

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Hi Kirk
As Andrew just said, 30 to 50M is a long track to get power to. This could be a bit complicated trying to find a suitable method of getting motive power to the carriage. You will find that looping a cable on a catenary is not as simple as first imagined. “ordinary” cable will tend to twist as it is slackened and straightened which leads to conductor failure, usually where the cable attaches to the loops on the catenary. I have got away with “ordinary” cable over about 3M by purposely introducing a twist and loop to absorb the natural twisting motion. I think the cable used in such circumstances (I may be wrong here) has a special twist something like the “non rotating or spinning” steel cable used in rigging applications where the twist in every second layer is reversed.

Over that distance if it were me I would be looking at a simple endless loop of something like strong cord type fishing line with a motor driven capstan at one end and a pulley at the other end tensioned by a spring. Loops could be fitted at intervals underneath to catch the natural sag in the line over this length and keep it out of harms way. The carriage still running on some form of track. If the carriage had to be stopped at specific spots this could be done with magnetic or some other sensors. I think this would be far more economical than toothed belt or rack and pinion. Rack and pinion has to have motive power available on the carriage by looping cable with above problems or supplied via conductive rails.
Cheers Bob


Hi Andrew

Starting again in the reverse direction is easy to do if you are using brushed motors. I posted a circuit to do just that some time ago, I’ll see if I can find it again. It involves fitting a diode across the normally closed connections with such polarity to allow current in the reverse direction when the contacts open to cut power to the motor. This allows you to reverse off the limit switch with the contacts open. Just as important is a diode switched across the motor to provide instant stop and prevent over run. This over run can be embarrassing if it is great enough to allow the switch to close again and keep going in a fault situation.
Cheers Bob


I think that you misunderstood the option that I was proposing.
‘NC’ microswitches at each end that simply disconnects the entire power for the unit as a safety.
In this application there is no data or other direct motor contact as the controller is sliding along with the camera.
It’s a bad design as not only does it stop you dead and require a manual intervention, but you also have to run the power to either end of the track before it attaches to the cart.

That’s not an elegant solution for Kirk as moving the drive motor to one of the track means that the drive signal needs to also be translated from the cart and Raspberry Pi all the way to one end, so the issues with moving a power cable with the cart doubles as you now also have to have a second cable for the motor power going the other way.

If a catenary is not suitable, I have another idea.
Have the power cable on a drum with a two pin slip joint:

again, using paracord in a loop with a capstan at the other end, you could drive the cable spool out drum in sync with the movement of the cart, just have a tray that runs the length of the track to hold the cable up.


Thanks so much @AndrewBG and @Robert93820. Now that I know the sort of ‘search terminology’, I have since begun making some initial enquiries. Yes, it would appear that for this sort of distance, rack and pinion may be prohibitive. Right now, we’re assessing how we can make this thing work. The two big issues we’re currently seeing are:

  1. Movement: how do we physically propel this thing up and down a track minimising bounce; and

  2. How do we supply power to it?

Does anyone know if power can be directly supplied through things like conductive strips etc. (e.g., similar to how a model train picks up its electricity)?


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Encapsulated around a slide track like my model will work.
You say and avoid bounce, are you intending to shooting video while the cart moves fast?

Conductive strips wont last very long in a high humidity environment, you’ll need insulated cables.


Hi Kirk
Would it be feasible to power the RPi/camera set up with re chargeable batteries and have the carriage moving power at either end like my endless loop/capstan suggestion or something similar. This would remove the requirement to getting power to the moveable carriage. The down side would be the requirement to change batteries or charge the complete set-up.

Another alternative could be a pick up system like an electric train or live rails as you suggested. I think whatever you consider is going to have its own set of problems and you will need to think out which set will be the easiest to sort out. But I think trailing wires would best be avoided if possible as over the distance involved would be pretty cumbersome but I think you have some thinking to do. It would help if we could eye ball the set up physically but unfortunately you are the only one able to do that.
Cheers Bob


Hi Kirk,

There’s a lot of great discussion going on here, I don’t have too much to offer except some a link to some parts that may cut down on the design work:

Keen to see where this project goes!

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I think Aluminum will wear quickly, especially in a dirty/wet environment. Also, I think pipe or round section will stay cleaner longer, I’d even think about having a spray near the wheels to wash debris and contaminants off the track.


Whilst I agree, it totally depends on where the track is located and how fast the cart moves.
If it is in the rafters, then it will be high humidity, but wont degrade as much as if it is on the ground.