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Old 11-26-2019, 03:12 PM
bnolan bnolan is offline
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Default Motorized sofa: 2x MY1020 BLDC, 1000w @ 36v

Heya,

I've been keen to build a motorized sofa for a festival. Something like but slower and with more torque.

I've ordered two MY1020 brushless motors, 36v @ 1000 watts. I've also ordered chain and sprockets, a 9t for the motor and a 92t for the wheel. I ordered a 36v 1000 watt controller as well.

My design for the couch is to have two wheels driven independently by a motor each, and use a playstation controller connected to an arduino to differentially throttle the motors.

I'll update this thread as I go along.

My questions are:

I'm buying some kart wheels with bearings in them, can I simply use a 12.5mm bolt as the axle to bolt these wheels to the kart?

I've seen someone mount the large sprocket directly to the wheel rim with some stand offs - is this a good solution for driving the wheel?

Will I have enough torque with 2 x 1000w motors and 10.2:1 reduction ratio to slowly drive a couch around a grassy paddock?

I'm excited about getting these motors because I can repurpose them to make an electric kart for year round use after the festival is over.
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Old 11-26-2019, 04:48 PM
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itsid itsid is offline
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one controller?
I think you will need two

lots of buttons for just the need of one joystick..
I wonder what you will use the rest for

kart wheels with bearings yes.. good choice
one wheel peel driven wheels (with sprocket) also a very valid solution

12.5mm bolts? never seen em..
but the correct size bolt in a high enough grade makes a decent one wheel acle;
just make sure it's securely fixed to the chassis.
(i.e. welded to the chassis and the nut holding the wheel in place)
12.5 however is nothing I would want to suggest really..

I'd go 17mm tbh.. (or at least 5/8" ~16mm)

I'd assume the 1kW motors have about 2.6-3Nm of torque each
with a 10.2:1 rating that'd end up in ~29Nm on the wheel times two
close to 60Nm .. should be good
but the question is what size are the wheels really
and that grassyness of the paddock itself can be quite the downer..

tough to say.. Tennis or soccer lawn.. sure enough no problem
a deep enough dip, a muddy spot or something and you'll literally be stuck
however.

'sid
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Old 11-26-2019, 05:16 PM
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Hi, thanks for doing the maths! And yes, I have two controllers, sorry missed that bit. The specs say 4nm per motor, so I think the couch will work ok - may need a bit of a push to get going, and probably can't go up slopes, but should be good on the flat.

For the speed controller, I understand I can use two PWM outputs from the arduino, with a smoothing capacitor, and wire that into the throttle control for the controllers.

And it seems like the motors run at different speeds in forward and reverse, I'm planning on mounting the monitors opposite each other, but hopefully I can handle the speed difference in software.

This is the controller I ordered:



I'm hoping the reverse works as intended, it'd be great to run the motors in opposite directions and turn on the spot.

---------- Post added at 12:16 PM ---------- Previous post was at 12:06 PM ----------

Quote:
Originally Posted by itsid View Post
lots of buttons for just the need of one joystick..
I wonder what you will use the rest for
Left joystick for steering.
R2 to accelerate
L2 to brake

x / square to turn lighting on / off.

And, you have to enter the konami code to turn on the motors (to prevent people "borrowing" it).
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Old 11-26-2019, 05:21 PM
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I'm not sure you even need or even want the smoothing capacitor really.
And while a true DAC would be ideal,
I think the pwm on an ordinary 328p is good enough to convince most controllers

since it is a PWM you have 5V high and zero low thus the cap will charge with 5V ..
and discharge with 5V as well (thus the controller might read full speed only.)
Since the typicall HE signal out of a throttle can be rather noisy (or say jittery)
the controller should have smoothing circuit built in which might get fooled by the PWM alone

Most controllers can not be switched in reverse without the brake engaged.
So chances are you need to brake one wheel in order to reverse direction
in order to prevent fying the controller or motor when switching in reverse going full speed ahead

A wheel speed sensor would be nice that way you can balance the laod between both wheels and properly adjust speed offset instead adjusting left and right manually
(one joystick instead of two.. one free gor more gimmicks gimbal nerf gun or such )

[EDIT]
oh too late..
well then yes you will NEED speed sensors on the wheels

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Old 11-26-2019, 05:33 PM
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Quote:
Originally Posted by itsid View Post
well then yes you will NEED speed sensors on the wheels
Does the motor speed come from one of the wires on the ESC or do I need to add a seperate sensor somehow? Could I poll one of the hall effect sensor wires to get a rough idea of the motor speed?

edit: Did some more reading, seems there are a few arduino sketches for reading RPM from the hall effect sensors.
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Old 11-26-2019, 09:53 PM
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well you could, but you'll need an OpAmp and a few diodes since the output is quite small
above the threshold yes..
but tapping into the signal can easily corrupt that (a floating pin can trigger the controller to assume a HE triggered that isn't)...
sooo yeah possible, not trivial
I'd rather had the speed signal seperated but that's your choice to make.

total partscount wouldn't change much I'd say
And since you're pretty much free about picking any type of signal
(magnetic, inductive, resisitve.. even an optical sensor picking up the sprocket teeth..)
you can use what you got laying around or what's easiest for you
to deal with.
You will want to keep the list of external libraries short,
and while the short code is the better one, you want the error checking routines to be exhaustive.
Especially if the arduino is the only thing talking to the controllers,
you wouldn't want it to perma set full speed in any direction without you being able to interfere by accident
32k is not as much as one might think and especially RAM get's sparse very quickly if you
have large reader classes for whatever sensor instead of making your own
(auto optimisation doesn't always work too well)

anyways.. a bridge to cross when reached

HE reading is mostly ISR based which is nice if all you do is reading the rpm,
but you will need ISR to run your command loops,
(brake at least!) so one's gone and with just one more you cannot get the rpm of two seperate motors AFAIK, not if the rpm counting is ISR based.

And while you only need to poll for the wheel speed once per loop
essentially, you will run into a timing issue if you swap interrupts (remove one attach another then again) if you need to wait for a full rotation or a timeout
the optical trigger on the sprocket is several times faster

tough decisions to be made ahead.
[EDIT]
uhhhh hang on..
'autometer signal'

that sounds like you HAVE a speed indicator output on the controller..
chinese auto translation is sometimes a bit fishy to say the least..
but that indeed sounds like a promising wire you have there

'sid
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Last edited by itsid; 11-27-2019 at 05:44 PM.
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Old 11-28-2019, 06:14 PM
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Oh good spotting - looks like the autometer signal is analog 0->18v with RPM!

https://endless-sphere.com/forums/viewtopic.php?t=96736

The "autometer signal" is interesting. It seems analogue (though probably just buffered PWM). The faster you go, the more voltage you read on this line. What's weird is that it hangs out of the controller, unprotected and uninsulated, but ramps up as high as 18V when the bike is at full throttle on a 39V pack. It's blue, and connected to "S+". I have no idea how I'd use this, though driving a regular analogue panel meter could be fun. :-)
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Old 11-28-2019, 06:35 PM
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if it's indeed rpm dependend..
then all you need is a voltage divider to lower the max
down to say 4.5V (4:1 divider) and you can feed it in one of the analog pins.
that way at any point in code you can just request both analog values
and compare them to adjust
Awesome!

Too bad I cannot spot an ISP header on the pcb..
ah well you can't always win I guess

'sid
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Old 12-01-2019, 10:13 PM
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Started work on the arduino code and frame.

Going to have individual control of left vs right motors, enforce that you have to be at a complete stop before reversing motor direction. Have a button that activates motor braking. Going to use two PIDs that take the motor RPM as input value and setpoint, and modulates the throttle percentage as an output.

For the frame I've decided to try and make it from aluminum, cross braced with structural plywood, and lots of nuts and bolts. I'm using 30mm x 30mm x 3m cross section. Will reinforce the axle mounts with steel.

Going to order 2 x 10ah 36v lithium battery packs to keep going on the 'lightweight' angle.
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Old 12-02-2019, 10:40 AM
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30 Amp draw on a small LipO pack can be be quite intimidating..
so check for the constant discharge rate of the batteries and be aware that 10Ah
might be depleted quicker than you think

Anyways.. keep us updated

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Old Yesterday, 02:14 PM
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Ok, cancelled the lithium battery order, going to use 3x 40ah 12v batteries.

Building the frame out of aluminum cross section bolted to 12mm plywood. Frame will be 1200 x 600mm. Wheels will be along the short sides so the couch travels forward in the direction you're sitting, and will have more leverage for skid steer. Using M16 threaded rod for the axles for the wheels, which should mean I can adjust the offset of the wheels to get the chain lined up nicely. Still waiting on electronics.
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Old Yesterday, 08:41 PM
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Nononono please do NOT use threaded rod as an axle..
a terrible idea really..

yes 16mm is actually quite a substantial diameter for a very short axle,
BUT it's still not going to work too well in he long run.
(the bearings inner race wants a smooth shaft to ride on, NOT pointy sharp threads)
Also threaded rod is usually rather soft material that's comparably easy to bend..
(even compared to a 16mm high grade bolt!)

using a grade8 M17 bolt instead would not only be a much stiffer solution,
it'd also allow you to use proper Kart frontwheel bearings AND shims!

that way you can make the alignment very easily as well as have a bearing and axle you can actually trust.

'sid
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Old Today, 03:50 AM
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Quote:
Originally Posted by bnolan View Post
Ok, cancelled the lithium battery order, going to use 3x 40ah 12v batteries.

Building the frame out of aluminum cross section bolted to 12mm plywood. Frame will be 1200 x 600mm. Wheels will be along the short sides so the couch travels forward in the direction you're sitting, and will have more leverage for skid steer. Using M16 threaded rod for the axles for the wheels, which should mean I can adjust the offset of the wheels to get the chain lined up nicely. Still waiting on electronics.
Quote:
Originally Posted by itsid View Post
Nononono please do NOT use threaded rod as an axle..
a terrible idea really..

yes 16mm is actually quite a substantial diameter for a very short axle,
BUT it's still not going to work too well in he long run.
(the bearings inner race wants a smooth shaft to ride on, NOT pointy sharp threads)
Also threaded rod is usually rather soft material that's comparably easy to bend..
(even compared to a 16mm high grade bolt!)

using a grade8 M17 bolt instead would not only be a much stiffer solution,
it'd also allow you to use proper Kart frontwheel bearings AND shims!

that way you can make the alignment very easily as well as have a bearing and axle you can actually trust.

'sid
I have to agree with Alex here. Threaded axle is a TERRIBLE idea. Those rods are usually of very inferior quality too, and they snap at the drop of a hat. Just don't do it.
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