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Heavy dump bed, slow servo needed.

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I plan to add a lifting bed on the Heavy dump using the 3rd channel. I think mechanically there are a few options that would work, but for all of them the action would be too fast.

Is there a way to slow a regular servo? Or can you buy high torque slow servos? Something around the 3 second mark would be perfect. 

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These may be too expensive for what you want, but it's nice to know something is out there for reference:

https://www.progressiveautomations.com/products/micro-linear-actuator

I've played with this before for about $9 USD, and it has all the guts needed.  It just needs a new 3D-printed housing to adapt it to the application.  Internally it has a circuit board, motor, worm drive, and limit switches.  Depending on which way you set the 3rd channel, the mechanism will spin the worm screw until one or the other limit switches is hit.

https://hobbyking.com/en_us/digital-servoless-retractable-system-1pc.html?queryID=dbd520a77de6269b5ff53a4040a2ba61&objectID=38770&indexName=hbk_live_products_analytics

I haven't gone the distance and installed a modified unit to my Heavy Dump yet; it's on the list of things to do.  But some initial exploration got me this far.

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A sail winch servo may do the job, they seem stupidly slow compared to normal servos (must not spend money upgrading cheap rts yacht...)

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Maybe look at aircraft retractable undercarriage systems?

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Thanks everyone! Trying to remember my a-level physics and mechanics in how I should set this up to get the maximum force. I've got a 15kg servo I'd like to use, as it would be going spare. 

The sail winch looks good, but I want the ability to lock the bed down, so just having a rope with tension to lift the bed wouldn't be enough.

image.png.da504452f130a8990a696ea47145da66.png

This was my first idea, a pair of servos mounted on the side of the chassis. Each one attached with a servo horn to a solid bar attached to the bed. As the servos rotate anticlockwise they push up the bar, raising the bed and as the rotate clockwise they pull the bed down. This means the bed can stay locked in place by the bars. The servos would have a strong servo saver to ensure they didn't break if the car landed on its bed. This is good idea, but needs two servos, which adds lots more weight, and I'd need to get a servo splitter perhaps a servo reverser as well as a servo timer dely.

The other option uses one servo, instead of pushing the bed up the servo sits on the other side of the pivot, pulling the bed down in the middle.


The servo is rated for 15 kg at 1 cm (I'm sure there's a SI I should be using 1.47 Nm?) but if I can keep the servo horn around 1 cm, that would mean that it can pull down with 15 kg of force. Although the force here is closer to the pivot (bad), I can utilise a smaller servo horn for the same amount of lift height, resulting in the same lifting force. 

This just uses one servo, but I won't be filling the bed with rocks so it should be fine.

The ultimate goal would be a truck that can self right, when on it's back using the bed to flip up the chassis to near vertical, then using inertia from the wheels (from flipping throttle backwards to forwards) rock the car back on it's feet. Probably not going to happen, but that would add such a cool element to the stunt truck! It's the kind of think Nikko would have made in 1995!

 

image.png

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19 hours ago, TurnipJF said:

How about running an ordinary servo and an in-line servo speed reducer?

There are many on the market. Here are some examples:

https://modelradioworkshop.co.uk/shop/servo-control-devices/servo-slow/

 

https://www.ebay.co.uk/itm/353816107838

 

https://www.ebay.co.uk/itm/324737055559

Thanks, I think this could be the one. I think I'll try a set up with a servo on channel 1, using a steering wheel to slowly turn and lift the bed. If it works then I'll get one of these to slow.

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It works! I will try and put in a video tomorrow....but it actually works. Need to order some nicer plastic to make it look better but I am super happy with it!

I went for option 2, one servo at the back pulling it down past the pivot to raise the bed. I actually found the speed was ok without a reducer, much faster than realistic, but that's the truck in a nutshell!

 Haven't done a strength test, but I feel it would do a scale load of gravel ok. 

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I need to add proper locking nuts and trim the servo horn, but here it is.

In locked position, bed down:

JKvTq8S.jpg

The arm pushes the bed up, so it sits where it should nice and flat. It feels pretty sturdy to me, it's a 15 kg servo, so there's a decent amount of torque on it keeping it in place.

When I press the button on channel three the servo is rotated anti-clockwise the arm swings down

xZSV0oE.jpg

This then pulls the back of the bed, lifting up the front of the bed up a few inches. It's a distance multiplier, so a small movement of the servo creates a much bigger effect at the front. Although this reduces the force available, if I had placed a servo near the top of the bed I'd have needed a much longer servo arm, which itself would have reduce the force, so it balances out. I've only got the total energy produced by one rotation of the servo to play with, and nothing I can do can cheat that! 

X19oqCL.jpg

This is angle at maximum lift, which is about as angled as you can get with the bed tilted on the original rear posts. 

When used for heavier driving I will lock down the bed using the original mounting holes and clips to avoid the bed flying off or the servo getting damaged.

6WQJelr.jpg

When the bed is down the holes are still perfectly aligned so the top of the bed can clip into the cab.

This mod used a single servo on channel three, a mounting plate made of 3 mm acrylic, servo mounting blocks, and then the pieces for the arm mechanism, which was an MF01x upper arm, servo horn and short dampener mount and bolts, although that's what I had lying about. I needed to drill two 3 mm holes, one in the back of the bed and another in the battery cover to attach the servo plate.

I'm sure someone could make a 3D printed version of this, and I'm happy to share dimensions if someone wants to make a proper job of this (although if they could share a prototype with me that'd be great!). Not sure how many GF01 owners there are, but it seems like a super simple mod that really adds something to an already cool truck.

Now the ultimate would be a system where the bed could flip to the vertical, which means a GF01 on its back could be pushed back on its wheels with a press of the button - how cool would that be? It would add a real new level to the stunts you could do, but that would need a much more powerful servo and probably a new mechanism on a dedicated hinge. Someone feel free to steal this idea, as I'd love to see that.

 

 

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