tamiya gearbox using solar panels?

[Hank Fletcher]

I was wondering if anyone might be able to tell me whether it's reasonable to try and power a small robot using a tamiya double gearbox with solar panels.

Presuming something like four solar panels about 4" square or so, with each about 400mV for a combination of 1.6V and maybe a short circuit current of about 1A, would that be enough to roll my robot around on a smooth floor? The weight of the robot I'd guess to only be that of the panels, gearmotors, wheels, a light chassis and r/c receiver, and not much else.

Am I dreaming, or am I in the ballpark? I just don't know how the short-circuit amps of the solar panels would compare with the current requirements of the gearboxes (I read somewhere between 1A and 2A stall, but I have no idea). Speed's not a big issue, but I would like it to be fun to operate the final product without wishing it only had a little more juice!

 

[Nigel Goodwin]

I suspect you will be very disapppointed with solar cell performance, those small panels sound woefully too small for the job.

I would suggest getting one and doing tests with it - bear in mind you are probably only going to get 50% or so of the rated value in Canada, even in bright sunshine.

 

[Hank Fletcher]

I've found the datasheet for the motor that powers the gearboxes, which states a stall current of 2.2A. I guess ideally I would plan on doubling that, seeing as there are two motors? Here's where I found the datasheet:
https://www.pololu.com/catalog/product/114?tab=resources

I'm not sure what to plan for in terms of voltage drop. It says max efficiency at 1.5V with 0.2A with no load, and then 0.66A at max efficiency? I'm just trying to anticipate conservatively here how much I'd have to get from the solar panels.

I would suggest getting one and doing tests with it - bear in mind you are probably only going to get 50% or so of the rated value in Canada, even in bright sunshine.

That's not a huge issue, I'm hoping. My plans for this robot are only to run in an environment over which I have a lot of control: a smooth floor in my brightly lit basement. I have a very small panel here I've been experimenting with, and it quite reliably reads .4V when it's sitting on the floor, but I can't seem to get enough current out of it to even light an LED when it's very close to a bulb? It's suppose to have a short-circuit amp value of about 0.5, too. Any further thoughts?

I don't mind going for a gross amount of solar panels, as long as there's a chance it might work. Still, the tamiya gearbox wheel base is only about three inches wide, so there's only so much I could do within reason!

 

[blueroomelectronics]

You're basement lights are no match for sunlight. Very little energy from a 100W bulb, even worse when you can't buy them anymore. A CF won't run a solar panel well.

That double gearbox can chew 1A on startup. About 150ma - 300ma per motor depending on load. Solorbots use weedy pager motors are that's about it.

 

[Hank Fletcher]

Okay, maybe the original goal isn't possible, but how about some help with this alternative?

What if I want to be able to run the robot at any given time, provided it's charged enough to run? For instance, the robot might be in my basement 24/7 with the light on, and it has an onboard battery and solar panel charging the battery. Then I just have to wait until it's charged before operating it again after wearing the battery/solar panel combination down.

Sorry, I probably should explain that for what I want to do, it's not reasonable to presume that the robot will be "docked" at a pre-determined position for the purpose of recharging after each use. For that reason, I came to the conclusion that some kind of solar power or tethering (the latter I really don't want to do!) was the way to go.

Any hints for the solar panel/battery idea? I'm not too sure what I should be taking into consideration, especially for determining the recharge time, and making sure the battery is charged properly (e.g. not undercharged or damaged). Any circuits, ideas, etc are greatly appreciated, as always!

 

[3v0]

Use a 15 minute recharger and having the robot dock with it.

If you can have the robot idle long enough to recharge using solar you should be able to come up with 15 minutes to dock and recharge?

If 15 minutes is too long have it exhange power packs at the docking station. That could be fun.

But if you want to use solar ....

 

[Hank Fletcher]

Use a 15 minute recharger and having the robot dock with it.

If you can have the robot idle long enough to recharge using solar you should be able to come up with 15 minutes to dock and recharge?

The trouble is, I won't necessarily be the one operating the robot, and I won't be able to trust that whoever is operating the robot will be responsible enough to return the robot to a dock when they're finished. That's why I thought the solar panel solution (and I probably should have said an enclosed environment) might be the way to go.

It's funny how you think about these things, though. I think it's reasonable for me to presume that every 24 hours or so I could take a minute to swap out a rechargeable battery pack. Presuming I'm using two sets of 1.2V AA batteries in parallel (the equivalent of 1.2V per motor), I could add as many as it takes to get the robot through a day. Obviously that could get critical, since the more batteries you add the more the robot weighs and the more power it uses. That might take some tinkering - I can't do the math in my head!

What's the point of it all? Well, how cool is this idea:
tamiya robot + reliable power source + enclosed environment + some tasks (race course, obstacle course) + webcam + remote control via Internet webpage + zealous forum members = ?

I reckon to make it happen.

 

[3v0]

Sounds fun. You could program the robot to see to its own power needs. Have it go recharge of get a fresh powerpack when needed.

"Sorry, I am going offline for 20 minutes to recharge"

 

[Hank Fletcher]

Sounds fun. You could program the robot to see to its own power needs. Have it go recharge of get a fresh powerpack when needed.

"Sorry, I am going offline for 20 minutes to recharge"

That would be cool! For once in my life, though, I'd just like to get the rough idea of it going first and not overthink it (as I think it's obvious that I tend to). I think I'll start with me trying to swap it out once a day, seeing what the usage is anyway, and go from there.

But what else do you think about this self-swapping idea? I'm thinking it'd be pretty easy for me to program the auto-battery-swap routine based on the webcam images and the software I'll be making for hosting the thing. Scan the video for two obviously coloured markers on the robot, and reckon position and orientation based on that. Then it could auto-drive through a battery station like the Little Loader:
https://www.youtube.com/watch?v=D1GaMTMvaeg
It'd be pretty easy to make the battery station area out-of-bounds for users using the video reckoning method, too.

I'm just thinking low-budget position and orientation solutions, you know?

 

[3v0]

I know what you are saying about over thinking. So often how things need to work and how one imagines they work are not the same.

The Little Loader looks fun.

Lots of ways to do the battery pack exchange. I was thinking of having the battery in a track-way on the robot. A solenoid pin could keep it in place. Energize the solenoid and the pack would be free to slide out of the track. Use the new battery to push out the old sort of thing. Many details would need to be worked out.

 

[Nigel Goodwin]

There used to be a 'Robot Olympics' sort of competition on UK TV, one of the events was a solar powered model car race - as it was indoors they had the largest bank of massive lights you've ever seen in your life! - think a massive sports stadium, now put ALL those floodlights in your basement (that's the sort of thing you're looking at).

Your puny basement lights would only be a tiny fraction of even poor sunlight.

 

[Hank Fletcher]

Your puny basement lights would only be a tiny fraction of even poor sunlight.

Which would explain my current, pasty complexion. I gotta get out of the house more this summer!

 

[Nigel Goodwin]

Which would explain my current, pasty complexion. I gotta get out of the house more this summer!

I think my pasty complexion is rather fatching?

 

[Hank Fletcher]

How many crank arms come with the tamiya double gearbox? The only descriptions I've seen are like this:
http://www.robotshop.ca/home/produc...gears-motors/tamiya-double-gearbox-70168.html

Does one double gearbox come with two crank arms (one for each side/axle)?