Hexapod Kit Design: MSR-H01

Hexapod Robots

Hexapod Kit Design: MSR-H01

Postby Matt Denton » Thu May 29, 2008 2:59 pm

I'm close to finishing the design of an aluminium hexapod kit MSR-H01, based on my V4b design. Please take a look at the features and CAD drawings and let me know any thoughts on design/features.

Basic Specs:
Servos: 6 x Hitec HS-225BB/MG + 12 x Hitec HS-645MG
Material: 3mm 5053 cnc water-cut Aluminium plate
Electronics: Will take standard size 2.7" x 2" hole electronics
Battery: Will take 4/5 sub-C or 4 x A/AA pack, along with 9V PP3 battery holder
Weight: Unknow at this time
Material Finish: Unknown at this time
Pay-Load: Unknown at this time
Kit Price: Unknown at this time

I'm working on two versions of the design, one has the electronics mounted upside down inside, and has no opening in the top. The second and currently more practical design has a hole in the top body plate to access installed electronics.

I'm also working on a standard size p.Brain motherboard (p.Brain-SMB) to fit the p.Brain-ds24 controller.

Design 1
Image

Design 2
Image

These designs currently use snap-rivets to mount the servos to the aluminium, although this is a quick and easy mounting method, I have not used these for any length of time, so if you have an opinion on this fixing method, please let me know. I could switch back to M3 nut and bolt.

Any thoughts?
Last edited by Matt Denton on Thu May 29, 2008 5:10 pm, edited 1 time in total.
Reason: Fixing hole dimensions corrected.
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Re: Hexapod Kit Design: MSR-H01

Postby paulp » Thu May 29, 2008 5:03 pm

Looks good...

I think the upper chassis plate should have the hole in it as it allows the mounting of other devices on the top while preventing cables from being run around the edge of the chassis.

Plastic rivets are fine. If anyone has difficulties with them then its a simple and cheap job to change them for bolts. Everyone has different preferences to fastenings, I personally prefer domed hex bolts as they sometimes make access easier.

I love the open look of the legs and the clever servo mounts at the top.

From my own preferences and from other peoples comments I've read, I like the open style of the V4b chassis. Its aesthically pleasing to the eye and the Femurs from V5 are perfect. I appreciate that V5 is much bigger and requires double femurs to prevent twisting.

With the Motherboard mounts you have shown you can also mount the Motherboard above the chassis as you've done with V4b. I've found it easier to mount it here as it keeps the batteries away from the electronics. Possibly a good idea as I had a charger fault that blew the cells and sprayed the inside of the pod with shrapnel. The board itself was protected.

Do you have an idea of the running time? Mine spends most of its time tethered to a power supply mainly because I've not yet found a good wireless camera to install. When I do I reckon I will need to uprate the batteries I'm using to give me a reasonable running time.

Will the servo horns be plastic or aluminium. Not really too much of an issue as people can upgrade them if they want to
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Re: Hexapod Kit Design: MSR-H01

Postby ucaboys » Thu May 29, 2008 8:52 pm

I agree with Paul about liking the open style (framework) of the V4b.
I prefer nut & bolt to fasten parts together - I would leave most of the electronics on top just to add a few more geek points to my project.
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Re: Hexapod Kit Design: MSR-H01

Postby Matt Denton » Thu May 29, 2008 9:40 pm

The open frame work of V4b I feel will be a little impractical, if the user wishes to bolt something to the hex, there won't be much to bolt too. Hence the flat top plate.

As Paul points out I am thinking the version with the hole in the top will be more useful and give various mounting options. I will do a render with the top mount option as you suggest paul.

The V5 design is quit a bit bigger, and kind of a different ball game.. maybe a MSR-H02??

I really don't know about running time as yet, but based on previous experience I would say 45mins plus.

Servo horns will be plastic as supplied with the servos, unfortunately I can't source the aluminium horns directly, but this doesn't stop the user from purchasing them from A.N.Other store and retro fitting them. The mounting holes in the aluminium are 2.2mm so will take M2 screws.

The options for nut & bolt fastening are as follows:

1) 3.2mm servo mounting holes: Use M3 nuts, bolts and a 3 to 4mm reducing washer.
2) 4.1mm servo mounting holes: Use plastic snap rivets, but the user can replace these with M4 nuts & bolts without needing 3 to 4mm reducing washer.

I have never been a huge fan of snap fasteners, but have to say they work surprisingly well.

What are the thoughts on the PP3 battery holder option.. useful/pointless? I will post a closer picture of it.
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Re: Hexapod Kit Design: MSR-H01

Postby Coilgunpower » Thu May 29, 2008 10:18 pm

NICE! I have been waiting for a kit. I love the electronics part but the actual building of it I am not so good at. Great to hear a kit will soon be available. How much will it be for the hexapod and servos?
Great job,
Justin
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Re: Hexapod Kit Design: MSR-H01

Postby Matt Denton » Thu May 29, 2008 10:26 pm

So here are few other ways of mounting the electronics:

1) Mounting electronics inverted on top and underneath.

Image

2) Mounting electronics inverted on top.
For this to work I would need to take more meat out of the top of the body, not a problem.. and could add more mounting options.

Image

3) Mounting electronics inverted underneath.
I think this is a pretty interesting way of mounting the electronics, I think a nylon washer may be needed between the PCB and top plate, but his gives lots of room for wiring underneath!

Image

And finally the PP3 battery holder, as you can see this is accessed from the bottom and is a sliding draw type.

Image
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Re: Hexapod Kit Design: MSR-H01

Postby Matt Denton » Thu May 29, 2008 10:30 pm

Coilgunpower wrote:NICE! I have been waiting for a kit. I love the electronics part but the actual building of it I am not so good at. Great to hear a kit will soon be available. How much will it be for the hexapod and servos?
Great job,
Justin


Hi Justin, welcome to the forum!

Not sure on cost as yet.. I still need to finish the design and sort out manufacturing costs, rest assured I am working to keep it as affordable as possible without losing quality. That's why this forum is invaluable to find out what people would sacrifice to save costs etc.. For example, people have expressed they would prefer the top plate to be more of a frame work such as the V4b design, however, the more holes there are.. the more machine time.. the higher the cost.
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Re: Hexapod Kit Design: MSR-H01

Postby paulp » Thu May 29, 2008 11:15 pm

Hi Matt...

I like the upper and lower mounting options, it also provides a further option. As you can see from my Lexapod, I am a firm believer in protecting as much as possible. Above my PCB I have mounting a piece of clear Lexan which acts a mounting plate for switches but also protects the pins and circuitry of the PCB below. If it stops bullets then it might stop my kids form ruining the electronics.

One thing I experimented with was an open frame, similar to V5 but with a 1mm piece of Lexan fastened below it. This gave a solid surface to drill and fasten to as wanted but maintaining the look of an open frame.

Whenever I buy something like this, I always avoid damaging or altering the product components themselves, I would mount something as inconspicuous as possible onto existing mounts and use that for my prototyoing and modding. It may be a vanity of sorts but to drill holes in it would somehow spoil it.

I assume the 9v battery is to provide a seperate supply to the electronics. Many of the designs I have come across use the Servo batteries to power the electronics through a regulator / smooting circuit. The argument against it is usually that you keep the elctronics stable when the servo battery goes down. In practice I've found there is no harm in using the servo supply as the batteries will have lost the ability to move the servos long before reaching the failure threshold of the voltage regulator.

Out of curiosity, what are the dimensions of V4b and V5, I've seen the images of them together but have little idea of the scale..

My chassis is 210mm long by 130mm at the widest point. The femur is 90mm centre to centre and the Tibia is 110mm from rotate point to tip.

It weighs in, batteries included at 2.3 Kgs... At full speed the bot can jump clear of the table. Amusing to do once but never again. I mis-placed a decimal in the code and instead of moving to 1500uS pulse it tried to go to 150uS at a very rapid rate. Not good.
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Re: Hexapod Kit Design: MSR-H01

Postby Matt Denton » Fri May 30, 2008 8:02 am

paulp wrote:Hi Matt...

I like the upper and lower mounting options, it also provides a further option. As you can see from my Lexapod, I am a firm believer in protecting as much as possible. Above my PCB I have mounting a piece of clear Lexan which acts a mounting plate for switches but also protects the pins and circuitry of the PCB below. If it stops bullets then it might stop my kids form ruining the electronics.


Yup.. I was thinking last night I could supply a acrylic/lexan cover to go over the electronics bay.

paulp wrote:One thing I experimented with was an open frame, similar to V5 but with a 1mm piece of Lexan fastened below it. This gave a solid surface to drill and fasten to as wanted but maintaining the look of an open frame.

Whenever I buy something like this, I always avoid damaging or altering the product components themselves, I would mount something as inconspicuous as possible onto existing mounts and use that for my prototyping and modding. It may be a vanity of sorts but to drill holes in it would somehow spoil it.


I see your point, but I'm not sure the open frame will work as well on this hexapod, you have to remember that his is 3mm aluminium, and the V4b & V5 use 5mm aluminium which is a little cost prohibitive. Will have a look at the design later.

paulp wrote:I assume the 9v battery is to provide a seperate supply to the electronics. Many of the designs I have come across use the Servo batteries to power the electronics through a regulator / smooting circuit. The argument against it is usually that you keep the elctronics stable when the servo battery goes down. In practice I've found there is no harm in using the servo supply as the batteries will have lost the ability to move the servos long before reaching the failure threshold of the voltage regulator.


I run all my hexapods from 4.8V, and so regulating to 5 using a standard linear reg doesn't work. The p.Brain has a built in 3.3V reg, but due to the higher power consumption of the ds chip, I found the processor would reset due to brown-out conditions when the servos were under heavier loads when walking. Even big caps didnt fix this! There is 5V LDO reg on the SMB board, so if using 6V packs or higher this could be used, but this very much depends on the servos and power demand. So the 9V is there as a clean power option.

Having said all that, I have fitted a DC-DC converter to one of my hexapods which cleans the supply up very well. This module takes 4.5 to 9V in and gives 5V out. I will probably offer it as a hop-up module at some point in the future.

paulp wrote:Out of curiosity, what are the dimensions of V4b and V5, I've seen the images of them together but have little idea of the scale..

My chassis is 210mm long by 130mm at the widest point. The femur is 90mm centre to centre and the Tibia is 110mm from rotate point to tip.

It weighs in, batteries included at 2.3 Kgs... At full speed the bot can jump clear of the table. Amusing to do once but never again. I mis-placed a decimal in the code and instead of moving to 1500uS pulse it tried to go to 150uS at a very rapid rate. Not good.


Body dimensions of V5 are 200mm from front to rear coxa mounts, and 120mm across at middle coxa mounts. Femurs are 85mm between centers, Tibias 120mm.

I will add the dimensions of the MSR-H01 later.
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Re: Hexapod Kit Design: MSR-H01

Postby ucaboys » Fri May 30, 2008 4:12 pm

Matt,

But as Paul states the design of the Ver. 4b caught my eye from the start above all others.
I understand about the cost issue - but that I would be willing to pay more for something that is more complex and better looking. I guess I'm the type of person that likes complex and complicated stuff just because of the challenge it provides.

About the mounting points I thinks there is an easy solution to it.
How about providing the basic mounting holes in the frames to mount the electronics inverted on top ( Just like you did on yours ) , and also provide a 1 to 1 scale template for a Lexan cover that can be attached to those holes but covers completely the top of the frame. That way if anyone needs to - they can make a Lexan or other material cover to any thickness they want and use it to provide more surface and mounting holes. This is compromise between all options.
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