Team Thrifty /Fifty Build Diary for Bitza

This is our build diary for our first robot, named BItza, so called because its made of bIts-of-this-and-bits-of-that

The theme for the robot is to re-use as much stuff as possible and spend as little money as possible.

I'll try and keep this up to date but firstly here are some early chassis photos. CAD designs to come soon. (Made in ProDesktop for anyone that went to school in the last 10 years!)

The chassis is made up of various types of steel, bolted and stick welded together.
The wheels and drive train are from a lawmover.
The motors, gearboxes, batteries and chargers came from 2 Argos value cordless drills at £9.99 each.
The ESC are two 2nd hand Electronize 15amp.
As for weaponry we plan on adding a flywheel made from a err... flywheel at some point but for the mean time I think it will stay a rambot.

[attachment=2:1cy2xgrk]1.jpg[/attachment:1cy2xgrk]
[attachment=1:1cy2xgrk]2.jpg[/attachment:1cy2xgrk]
[attachment=0:1cy2xgrk]3.jpg[/attachment:1cy2xgrk]

It has been a while since I have updated this but there have been quite a few changes in that time!

The plan for this build was to make a robot for under £100 (hence Fifty/Thrifty). And so far we are on budget! The plan has changed and we are now aiming to make a Rambot Featherweight, instead of a spinner.

Here is the budget so far!

Drill Motors £20 (£10 each)
ESC 30amp £35
Radio Gear £15
Chopping Boards £20

Total: £90

The frame is made from scrap steel that was lying around the workshop. The wheels and mounts are from an old Lawnmower and the batteries are from old RC car's we owned. 7.2 NiMh 3K mAh.

Unfortunately the batteries are completely different in makes, previous use and rate of discharge. They just have the same stats and yesterday one of them shorted out while in the robot for reasons I can't find. So a bit of a step back unfortunately.

For charges we are using the ones we happened to have with batteries, which are rather old and charge incredibly slowely....

None the less though the build is coming along quickly! We do need to have a weight in though. Any suggestions of how to do this accurately?

Here's a photo of the robot so far!

[attachment=0:2g80c7zu]Bitza with Armour.jpg[/attachment:2g80c7zu]

looks like my kind of robot :proud:

Quick update;

We have added some bike tread to the wheels, since we had some issues with too little ground clearance and minimal traction.

The radio tray has been re-designed to sit deeper in the robot to help keep it safe. This will also allow us to have a much deeper angle on our front scoop.

The tails on the chopping boards have been removed (see above photo) since we found they can be prone to snapping, and wouldn't want our entire armour breaking off if we were to land on them.

The Rx for our 2.4Ghz system has stopped working on us, in the process of replacing it.

Making up some spare battery packs from the drill's NiCad packs, better than nothing!

Designs have been made to give the robot some ears to stop it resting on it's sides without wheels, and designs for the scoop have been made. Rather close to the weight limit, so hoping we can do whats left within it!

Made some more progress with Bitza.

Today we added the scoop on the front. Unfortunately due to the impending weight limit we couldn't use as sturdy a metal we could have hoped for.

The scoop is supported by 4 thick steel guides which are bolted to the robot's main chassis, which will help take the main brunt of impacts.

Still waiting for the new Rx to arrive (since the old one broke) and seem to have a bug whereby the robot is moving very sluggishly despite the batteries still putting out a voltage above their rating.

[attachment=2:bvhztuqb]Bitza with scoop 5.jpg[/attachment:bvhztuqb]
[attachment=1:bvhztuqb]Bitza with scoop 4.jpg[/attachment:bvhztuqb]
[attachment=0:bvhztuqb]Bitza with scoop 3.jpg[/attachment:bvhztuqb]

[attachment=0:1ajk2bsd]Bitza with scoop 1.jpg[/attachment:1ajk2bsd]
[attachment=1:1ajk2bsd]Bitza with scoop 2.jpg[/attachment:1ajk2bsd]

its looking awsome mate good job

I also think you have done a great job....I like the fact you have made it from bits and bobs. True roboteer attitude. :)

Cheers! It'll be interesting to see how bits and bobs holds up in the arena.... Unfortunately we didn't happen to find some scrap Titanium.....

When will you put up the CAD for the robot?

Oh yeh! Forgot about that. I don't have it, my team mate made it up. It's changed quite a bit but I'll try and get a hold of it.

Yeah nicely done guys. Looks much more competitive now aswell :)

Looks great & fairly original too. Nice to see something not come out of a CNC machine nowadays.

Two points though -
Is that scoop Ali? My 3mm Ali has bent under hit from a spinner. My 8mm has distorted slighty also but they were both flat panels so...
You'll probably need a back panel - it's a bit too open.

It's a lot more rustic than we originally intended, but that's to be expected. Originality was what we were hoping for, its out only strength!

Yeh the scoop is ali (the side of a dish washer.....) Think of it as ablative armour....

The trouble is we hit the weight limit a lot earlier than we thought we would (how do you guys do it!) so our intentions for something more sturdy got interrupted. To be honest hearing that 3mm ali didn't just get obliterated by a spinner is good news!

As for the open sides they were partially intended, with the thinking of the less to hit, the less to get hit! As it turns out not having sides is a great (and necessary) weight saver!

I like the idea of using a side of a dishwasher as a scoop and your robot looks good for a beginer.
Just one question, How much is the ground clearence? As it doesn't look very big from the pics.

Quote:

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I like the idea of using a side of a dishwasher as a scoop

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I don't! I doubt it'll stand up too much to be honest.....

The ground clearance is - from the front it's nothing (the scoop scrapes along the ground) from the sides is not much more than the head of the round heading coach bolts it uses as skids.

I wouldn't know if it's big or small having never seem another FW in the metal/plastic. It's dimensions are roughly 45 x 30 x 20 cm.

It's not the best to have no ground clearence at the front, as the scoop may catch on the floorboards of the arena.

It's OK, I can just bend the scoop into shape with my hands......... Think of it as adjustable ride height that I can alter dynamically to match the current fighting environment.

You could have a caster/roller just behind the front.

Update:

The new Rx arrived and is installed. It doesn't look right having something new in the robot, I may scratch up the surface a bit to make it fit in.....

Our welder has packed up, so the final parts of the robot have been bolted in place instead. Not ideal but it'll have to do for now until we get that sorted.

Not entirely sure what's going on, but I think one of the clutches in the drill motors has decided to start slipping, so need to check the grub screws.

Had a weigh in and found we are about 100 grams over the limit, so need to shave that off somewhere.

Added some upright supports at the front of the robot, that act as supports for the scoop and as mounts for the side ears.

Then as a test of strength I decided to stand my lardy (15 stone) arse on the robot to see if it could take it and it does no problem.

So almost there! Just a few things to iron out and we'll be ready for Birmingham.

Ohh and I'm sure if we where just to wash all the mud off the robot (it's mostly made from an old lawnmower) it would drop some weight........

My advice would be to remove the scoop ...it'll be nothing but trouble.

Really?

I'm fairly certain that the scoop will bend so much during any impact that it's distortion will probably lift the drive wheels off the floor.

Try dropping it ...scoop down and at an angle..... from knee high onto the ground this will simulate a gentle bump....chest height for rough and tumble and head height for a decent impact.


See what happens.

Hhhhmmmm, this had crossed my mind.

Guess I need to think up something!

We are almost done (although we have been saying that to ourselves for a while now!).

The robot it now within the weight limit, all of those bugs mentioned earlier have been fixed and some fine tuning has been done.

Ears and front uprights have been added, so not much more we can add to the robot now.

We do have one nasty bug though, where we seem to be about 75% down on power and can't figure out why. Unless we get this sorted before Birmingham then we will be useless in the arena.

Hmmm... What was the EXACT setup when everything seemed ok?

What transmitter and receiver do you have?

How is the mixing done? .... I seem to recall some transmitters that have a 50% speed reduction with the onboard mix.

Finally try driving on left and right stick with NO mixing see if that improves the speed.

NOTE: One slow motor would give your bot an awful drive line / curve ...it'll be permanently turning towards the slow motor.

The EXACT setup was, two 7.2v NiMH bats in series (with the link separating them), connected in parallel to 2 15amp Electronize ESC (each with a 25amp fuse), these then connected directly to the drill motors. The Tx was the Radio Link T4UE and the old 6 channel Rx. Nothing else was in the chain, no light, mixers, external failsafes, nothing.

The power drop happened after some modifications, which are as follows;
Now the Rx has been changed to the newer 7ch option (since the old one broke). The fuses were increased to 35amp, I added a power light and I neatened up the wiring, which included shortening some sections and lengthening others to make the whole thing sit better.

Other changes included, adding bike tread to the wheels to improve traction and ground clearance, (since the old wheels where smooth and barely stuck out from the chassis) straightened the chassis so that both wheels have equal clearance on both sides of the bot, re-made the motor mounts (old ones came loose) and tweak the wheel mounts so they spin free and smooth with no fouling. I then conditioned the batteries and ran the bot to find the current issue.

One thing that has changed is the new motor mounts grasp the drill motors on the piece of plastic above where the grub screws go in, before the shaft exits the gearbox. They grasp it with downwards and side force. Could this be inhibiting the motor?

We also found that the robot no longer drove straight, one side had a lot more power than the other, whereas before it drove straight and true.

We don't use a mixer, just old fashion tank steer on the 2nd and 3rd channels of the controller.

My initial thought was that the motors had just accumulated crap over time inside the motor casing, but we had taped the air vents at the very start to stop this.

Any ideas?

Certainly sounds like a fudged motor.

Connect a battery straight to each motor ..you should be able to notice a difference if one motor is considerably slower.

I doubt that the mount makes any difference...you could of course loosen it temp.

Quote:

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Originally Posted by PJ-27

My initial thought was that the motors had just accumulated crap over time inside the motor casing, but we had taped the air vents at the very start to stop this.

Any ideas?

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Could the motor have over-heated?

i had the same problem and honestly, change the motor, much less hassle

I slackened off the mounts to their minimal point without just dropping the motor and it seemed to make little difference.

It would seem odd that the motor would over heat, we haven't really ran the bot much, 10mins run time max, and none of those times were extended beyond a few minutes.

Maybe I'll swap both the motors out and see if that improves things, if that doesn't solve it then I guess having two extra motors isn't a bad thing. Process of elimination it is!

Just swap the one that doesn't work, if one works, why bother swapping it?

If one broke so easily then it seems likely the other will be suffering the same. They both go through the same treatment......

sometimes parts just go for no good reason. Swap it out for another and off you go.

Bought two more drills, I'll hack them and put them in the robot over the next few days. Hopefully that'll solve the problem, I'll let you know how we get on.

For those of you wanting cheap drills by the way, VoucherCodes.co.uk has a 15% off voucher at the moment for B&Q who sell £9.98 cordless drills. So that's £17 for 2 drills.

Swapped in the B&Q drills and it looks like problem solved!

Now to get in some driving practice before Birmingham!

Is the champs your first event? :rofl:

Yep!

O I have got my second fight at the champs with you :rofl: