Rigid Robotics Build Diary - Flat Damon

[lowndsy]

Hello everyone. Pleased to meet you. I'm Steve and being 35, Northern and single I have decided to fill my days building a robot. Apparently it is some sort of midlife crisis thing but that's fine, at least I didn't buy a Harley.

I'm starting off with a wedge featherweight based around being really structurally rigid. I have a solid ribbed chassis that I will be insulating and covering with Polypropylene armour. Bolts, grip rivets and screws will anchor the skin to the chassis almost every cm so it should be pretty strong. A layer of rubber sheet will spread the force of impacts and if weight allows I'll protect the corners with angle alu and corner brackets.

The design is currently a wedge but once I understand the weight implications I can tear into the chassis pretty easily so there is the option to cut the nose off to accommodate weapons, scoops etc. I know you are meant to start at the weapon and build around it but the main draw for me is seeing exactly how rigid / durable I can get it, so that needs the frame to be designed first.
The aim is to get to a localish event and for the robot to stand half a chance against any featherweight spinners it comes across.

The whole thing is on a budget while I knock up something that runs. When it comes to competing I'll have a think about investing to upgrade weak components, but atm the total budget is < £150 for V1. I have the chassis / some armour sorted already so I can definitely get her running for that.

For motors I am starting cheap with some cheap Chinese drill motors / escs from Amazon and I'll swap them out later if it looks like a goer. Going for ~24v if poss for a bit of grunt.

Potential names... I am watching the film The Martian a bit more than is healthy so at the moment I am thinking "Flat Damon" but with the armour being an integral part of the rigidity theme "Stressed Member" is coming a close second.

Photos to follow - currently it's just a big yellow chunk of chassis, but the motors and receiver are on order, should be arriving in my Amazon locker any day now.

Peace!
Rigid Robotics

[lowndsy]

Pics

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Chassis

[lowndsy]

Started on the internal armour supports over the weekend. I am using the trusty chopping board for some internal bulk and better quality Polypropylene for the outside.

Turns out small plastic chopping boards from Poundland come with 37mm holes that match my motors so I am using them for a bit of extra support behind the gearbox and they smarten things up nicely too. If I keep them away from the body of the electric motor will the gearbox generate enough heat to melt them?

[lowndsy]

100mm wheels ordered, looks like I'll need a reduction drive to keep it under control.

Dunno whether to use a chain, belt or gears. I only need 1.5:1 - any suggestions?

[maddox10]

A normal cheapo drill runs around 800 rpm on the chuck@nominal voltage.
With a 100mm wheel you will reach 15km/h. (low avarage for a feather)
Overvolting will result in a proportional higher speed.

Why the extra gearing?

[lowndsy]

I picked up an unused MFA motor off an acquaintance a while ago so I just had to buy one more to get the set. Took me a while to find the same one because I think it is discontinued or not as popular as their other models being a Spur.
Probably not the motors I would have chosen without a nudge but much better than my other Chinese ones (Beetle project anyone?).

It's a 540 11:1 5-15v Gear motor rated at 1430 rpm 12v no load so with ~4 inch wheels that's a bit rapid.
I'll probably pair two 7.2v lipos for 14.4V so I think I need an extra ratio to crank it down a bit. Bit worried it would just squeal and burn the motors out without lower gearing.

[maddox10]

With that explanation it's logical, and the extra gearing is needed.

Also, make sure the wheels can't transfer shock directly to the motors. So belt is your best bet. Support the gearbox shaft on the outside too.

[lowndsy]

That was going to be my next question. Originally I was going to isolate the drive from the motor with a universal joint and just extend an axle out from the other end with a couple of bearings to hold it, but now I need to gear down and support it as much as I can to protect all the moving parts.

Is there a standard way to do it or does everyone do it differently? Also, Does anyone know anywhere particularly good for the parts? Motor shaft diameter is 6mm, wheel bore is 8mm. If I can just buy a 1.5:1 gear or belt reduction drive from somewhere that would be ideal.

[lowndsy]

Big bits ordered

So this week the postman is bringing...

• The other MFA motor
• Absima Transmitter / receiver
• Mtroniks Tank signal mixer
• 2 100mm polypropylene wheels

I still need to order a few key things :

• Belt pulleys (alu?)
• Belt (10mm?)
• Speed controller(s?)
• Batteries (2x 7.2V?)

Building the drive belts is the hardest part left to do. I can't mount the pulleys straight on the plastic chassis so I need a little enclosure for it. I'll know more when the wheels arrive and I can measure up.

[lowndsy]

I was in Lidl at lunchtime and they have some mini 12V electric compressors for £12. There was one with a bashed plug for a fiver so I picked it up to see what the motor is like - might be another Beetle in the works... Will strip it down tonight and have a look.

Some of the internal fittings and gubbins will probably come in handy for Flat Damon too.

Update - motor is too heavy, went in the bin, but I got a bunch of fixings and plate mounted bearings out of it that will come in super useful. Might even have the full motor and belt mount if I'm lucky.

[lowndsy]

Most stuff has arrived now, will have a go at mounting the motors this weekend.

[lowndsy]

I just read the manual and the receiver only has a safety on channel 2. Do I need a "safer" one?

[Danjr1]

You'll need the receiver to failsafe on all channels you're using outputs from. What radio gear did you get?

[lowndsy]

It's an Absima 3 channel gun style so when the bot flips I'll just swap hands. I think the model number is cr3p. The 4 channel version probably has quite an unfortunate name...

Receivers aren't that expensive so I'll just build with this receiver and then swap it out when I'm ready to compete.

[lowndsy]

20161009_201814.jpg

Test fitting a motor. Plenty of space for a belt drive, but protecting it from damage might eat a lot of weight.