Team MedBots

All things antweight

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Max
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Re: Team MedBots

Post by Max » Tue Apr 14, 2015 9:54 pm

Probably true! We do have a small cnc milling machine which hopefully they will get going soon so that could be an option. The reason to go for the beetle motor is should have a lot more power so I can get some decent speed and should accelerate quickly. Also they only cost a couple of quid so I think it's worth trying to get one to have a play about with to see what can/can't be done.

Max
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Re: Team MedBots

Post by Max » Tue Apr 14, 2015 11:13 pm

From looking on FRA forums apparently there is only a single stage reduction of around 5:1, I was expecting 2 4:1 stages giving 16:1. This means I can just complety remove the gearbox and drive the wheel directly off the motor (hopefully). It will probably draw quite large current for an antweight so may need a large battery but hopefully should be able to get it all in weight.

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Rapidrory
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Re: Team MedBots

Post by Rapidrory » Tue Apr 14, 2015 11:34 pm

The motors are 40g each... though make sure you get the ones with the plastic end cap rather than the metal endcap as they have more power... It may be worth having a look round to see if you can find any without gearboxes; they'll likely be a fair bit cheaper...
Rory Mangles - Team Nuts

Robots: Nuts 2 and many more...

NanoTwo Motor Controllers: https://nutsandbots.co.uk/product/nanotwodualesc

Max
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Re: Team MedBots

Post by Max » Wed Apr 15, 2015 10:02 am

40g should definitely be workable even with a 3s battery. Easier said than done finding the bare motor, eBay and AliExpress aren't coming up with much that is suitable, mostly it is smaller motors around 30g and only 6v which I fear will lack enough power.

Can anyone who has bought beetle motors from AliExpress remember which seller they used, if I know which ones sell good motors I can contact them directly to see if they episode be prepared to sell the bare motor.

But as usual I am impatient and would rather get one off a roboteer in the UK so I can get playing.

Max
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Re: Team MedBots

Post by Max » Wed Apr 15, 2015 11:30 am

Here is a test vid using a 9v block battery directly connected to a speed 400 motor:
http://youtu.be/TPPD3i9vUeA

It's fairly disappointing! It may be that the block battery cannot deliver the current but I think the motor just lacks the torque required as it is a high rpm motor (18000rpm no load). The beetle motors should be around 4800rpm so will hopefully have the lower speed and higher grunt needed to move the robot.

Max
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Re: Team MedBots

Post by Max » Wed Apr 15, 2015 12:52 pm

Turns out it was the battery! Hooked up a 2s lips and the result was insane, it had enough power to spin but was way too fast and out of control and the wheel just flew off!
http://youtu.be/EkyPpkz-ki8
Perhaps with some speed control it would work a bit better but I think a slower motor would probably be better.

Max
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Re: Team MedBots

Post by Max » Wed Apr 15, 2015 2:56 pm

Here is what I have been working on so far:
http://youtu.be/0JrpqfPtPyg
It's just using ordinary ant weight gear motors as I had them laying around. You can see it translating all be it incredibly slowly and the direction isn't very consistent as it struggles to keep track of which way is forward but that should be fixable by changing a few parameters in the program.

Hopefully with faster motors it will translate better and look a bit more threatening!

Max
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Re: Team MedBots

Post by Max » Mon Apr 20, 2015 7:33 pm

10:1 HPs arrived from Harry today so replaced two of the three motors with them and was initially disappointed with the speed, it was faster but not fast enough to do any damage but then I remove the wheel from the one remaining slow motor and then it went crazy fast! In the first test the receiver which was just hanging out the top came uplugged and flew away, this meant it just kept going at full speed with no way to control it so trying to stop that was fun!

But after a short while a problem emerged with one of the motors, I started the motor and it had lots of power and spun the robot then after about 5 seconds it would start screaming and come to a stop, when you pick up the robot the wheel starts spinning again but can be stopped really easily. Then when you turn off the motor and then bring the power back on again it works and has lots of power again!
Any ideas what's happening?

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joey_picus
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Re: Team MedBots

Post by joey_picus » Mon Apr 20, 2015 9:36 pm

Is it possible you're drawing too much current after a while from friction during translating or even just from centrifugal/petal force? From experience with those 10:1s it doesn't take too much to stall them on 2 cells.
Joey McConnell-Farber - Team Picus Telerobotics - http://picus.org.uk/ - @joey_picus
"These dreams go on when I close my eyes...every second of the night, I live another life"

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Rapidrory
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Re: Team MedBots

Post by Rapidrory » Mon Apr 20, 2015 9:44 pm

Sounds more like dodgy bearings to me..
Rory Mangles - Team Nuts

Robots: Nuts 2 and many more...

NanoTwo Motor Controllers: https://nutsandbots.co.uk/product/nanotwodualesc

Max
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Re: Team MedBots

Post by Max » Tue Apr 21, 2015 9:57 am

Right, figured out what is happening, the shaft of the motor with the pinion in it is moving forwards (out of the motor) so disengaging with the driven gear. I've checked otheir motors and all the shafts have some play in them but in this one it can move a lot further.
Does anyone know how the shaft is meant to be restrained? I took the gearbox off a different gear motor to see if I vouif see how it was restrained but I couldn't see anything, perhaps there is some internal circlip or something?

Max
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Re: Team MedBots

Post by Max » Tue Apr 21, 2015 6:10 pm

Hmm, just tried to replace the HP motor in the 10:1s with one from one of my other gear motors but found the pinion gear was smaller than the ones in the 10:1s so there goes that idea!

I was thinking if I could find those LP 10:1 for a couple of quid that Rory found then I could just replace the motor with one of my HPs but I guess I would have to find a way of replacing the pinion gear.

Max
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Re: Team MedBots

Post by Max » Sun Jul 26, 2015 1:28 pm

Need to order a HP 298:1 gearmotor from polulu, I see there is a choice of long lasting carbon brushes or precious metal brushes. I've never used the carbon brushed ones, are they any good? I fear the brushes whikst longer lasting may be more liable to breaking due to shock impacts.

Can someone who has used them or knows more about them please enlighten me?

Thanks

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EpicentrE
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Re: Team MedBots

Post by EpicentrE » Sun Jul 26, 2015 3:16 pm

Ooh, that's certainly a new development! They didn't have that option last time I purchased any.

As far as I can tell, the precious metal brushes are the ones the motors have always had. I've had to dismantle a couple to repair the brushes and I'm sure I recall them looking like that. These are motors that have served me well in every robot I've built for the past 6 years or so, and I've only ever damaged the brushes when running them in high-torque scenarios (tracks, for example) on 3cells, and even then it's only been twice as far as I can recall. Personally I'd stick with what I know works, but I'd be interested to hear if the carbon-brushed ones had any noticeable difference in performance.
Scott Fyfe-Jamieson, Captain of Epic Robotics. Champion of AWS38/41/42.
http://www.epicrobotics.co.uk

Max
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Re: Team MedBots

Post by Max » Sun Aug 02, 2015 4:49 pm

Hi,
I'm trying to make a simple control board for that motor based around an ATtiny85 chip programmed using an Arduino. The program itself it very simple, it monitors the throttle channel and when it goes above half way motor is turned on, then it starts waiting for a button to be pressed, once button is pressed motor turns off. Finally it waits for the throttle channel to drop back down bellow half way and then goes back to the start waiting to go again.

I got it all working well on a breadboard but now need an actual PCB. I've tried designing one of fritzing but as per usual when I try to design pcbs all the connections are confusing, messy and require a few jumper wires. Is there anyone more skilled than I who can design a pcb for this circuit:
motor controller.png
motor controller.png (167.65 KiB) Viewed 3090 times
The best I've done is this:
motor controller board.png
motor controller board.png (183.42 KiB) Viewed 3090 times

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