Thread: Hand operated trailer mover

Hey guys looking to build a hand operated trailer mover that is silent to use loading the boat up at 3am

I need some help with a 3 stage shaft sprocket set up there will be a bottom sprocket on the wheels driveshaft, there will be 2 sprockets on a mid height shaft two different size sprocketsto convert the torque, than a top sprocket which a handle attaches to also the handle will need consideration on length as to easy the load

Will be using dirt bike front and rear sprockets some i have looked at the front are 6cm rears are 23cm

Anyone know the ratio or even the output in distance if i were to go with this drive combo

Top 6cm diameter to drive a mid 23cm diamter which will have another sprocket next to it on the same shaft 6cm diameter to a bottom final drive shaft sprocket of 23cm

23:6 is a reduction of 3.8:1
You're doing that twice so the effective reduction is 7.6:1
Assuming the numbers listed are diameters then the 6cm sprocket has a circumference of 18.85cm
18.85/7.6 = 2.4cm
Move the first 6cm cog one rotation the final drive will move 2.4cm
or...
360 degrees of rotation at input will result in 11.9 degrees of rotation at output

A tooth count of the pulleys is a better way to establish the reduction

Originally Posted by racingtadpole

23:6 is a reduction of 3.8:1
You're doing that twice so the effective reduction is 7.6:1

3.8:1 reduction applied twice. Wouldn't that result in about 14.5:1 reduction

I used a online pulley calculator and it looks like i will need 4 large and 4 small sprockets to complete a gear reduction drive over 4 seperate shafts

Sussed out a 500watt scooter motor online and they are silent and outputs 1.4nm at 3000rpm but if i can design and weld together a gear reduction frame and a wheel mount with some kind of attachment to the trailer and a cranking handle i will be in business

Thanks for the calculation guys, i will likely start building it this week

Originally Posted by GuzziJohn

3.8:1 reduction applied twice. Wouldn't that result in about 14.5:1 reduction

Yah, it is..
I’ll go back to leaving the keyboard alone while I’m on nightshift

A couple of thoughts.
Nm is a unit of torque or "force"against a resistance. So we need to know the "resistance" first, to work out the "force" required to move it. So the weight of the boat an trailer loaded ready to go is needed. Then this weight (mass) can be used to calculate the rolling resistance to be overcome. Keep in mind that the slightest slope or undulations make a huge difference!
A 500W motor is only bit more powerful than a fit human (at around 325W) and a little less than a horse (at 745W) [historical joke].
The torque of 1.4Nm multiplied by 14.44 (gear ratio proposed) makes that about 20Nm at 207rpm with a 300mm diameter wheel. That translates to a speed of 3.25m/s or 11km/h. The torque is equivalent to pull the 300mm wheel along is only about 13.6kgf (the force required to lift up a 13.6kg weight.
I think that is still way too fast and nowhere near the force required to move a trailer/boat/outboard/fuel/fishing gear/beer combination.
A wheel of only 200mm diameter will give you a third more pulling force at a third less speed, but I suggest you go for a much bigger sprocket ratio and a lit less speed. The sprockets and chains used on scooters are about 6mm pitch and tiny. Common ratios on scooter are 8teeth to 40 (1:5). Two sets of those would give you 1:25 reduction and some reasonable torque numbers at 35Nm, 36kgf at 120rpm or 0.36m/s = 2.26km/h with a 20mm dia wheel.
Even that might not be enough to move the trailer from rest.... You could check the actual force required with fishing scales hooked to the draw bar and pulled with your hand or two to see what it takes and then work back from there.

Thamks heaps for that last post Jhovel the scooter sprockets are tiny about 4cm and 13cm i am considering making my own 30-35cm sprockets and run it with a 4cm sprocket, the boat is pretty big weighs around 1600kg and is 7 meters long on a tandem trailer

Hand cranking would be ideal but i need to move the trailer a good 10-15 meters so might be tiring if i go 10 winds to move the trailer 20cm over 15 meters

I lookedinto the scooter motors as they are silent, at the moment i have a 550watt dc 12volt 950:1 gear ratio planetary gearbox/motor oushing the boat but its very loud

I'll grab some scales tomorrow and hook it up to the car tow bar with a comalong

Think i worked this out corretly a 25H sprocket has 1/4" link so a 350mm diameter homemade sprocket will be 183 tooth sprocket which will be roughly 1:37 ratio motor will be a 2500rpm which i will get a 67rpm output using a 5 tooth output sprocket and 183 tooth drive sprocket

67rpm at the axle is still way to fast being a 400mm diameter wheel

The boat was bogged in mud divets under all 4 wheels about 35mm deep i just pulled her out of it than hooked up two 45kg luggage SCA scales in series and straighten both hooks than snapped one end pin managed ro get a reading of 74kg in amung a lot of over load errors as soon as i eased off the come along the scales locked onto the weight

Going by the 45kg overload and how the comealong felt under load i would say the load was 80kg'ish with one side of the wheels pulling up the side of concrete driveway

I would estimate once the trailers on the concrete ready to roll it would only need 45-50kgs to move it

To test it again i would need to order a 300kg scale something the hooks wont straighten out

I looked at the #25 sprockets i can use 3 sets of 11 tooth and 76 tooth for 1:207 ratio output will be 12rpm

Why did you have the two scales in series and not in parallel?

Hay Gav i didnt think of placing them parallel

Just getting a hang of all these conversions, ran a watt to newton meter convert based on 500watt motor at my end drive of 12rpm and quiet surprised the output is almost 400nm and if i step up to the 1000watt scooter motor the output will be almost 800nm!!! That is like a high powered worked v8 cars torque

My last ford v8 had 350nm at of power if that is anything to go by

Take into account the reduction ratio required to get your 500W motor from 3000RPM at the motor shaft to 12RPM at the drive wheels, it's 250:1. Three stages of 5:1 reduction is 125:1, and you still need another 2:1 to get to 250:1 and 12 RPM. The more stages of reduction you use, the greater the power loss in the drive train.

Also take into account that a 350 diameter sprocket on an axle with 400 diameter wheel/tire means that the sprocket is running 25mm above the ground surface, assuming that the tyre remains fully circular, i.e. doesn't squash down at the contact/load transfer point. In that condition, it has minimal contact area with the ground and most likely will not transfer the torque, i.e. it will spin rather than draw the load. Allow a lower tyre pressure to get more contact area and pulling power and the sprocket and chain get closer to the ground surface.

Also 500W from a normal 12V car battery is 40+ amps for the duration of the pull, probably closer to 50A as the battery voltage will drop under load and the motor will draw more current at the lower voltage. From memory, when you first started discussing this some time ago, there was a steep incline between where you were parking the boat and the street. This will increase the current draw significantly, and I suspect that a car sized battery wouldn't complete the climb. Increasing the reduction ratio would reduce the load on the motor and hence the current draw from the battery, but also slow down the transit of the boat, meaning that the battery needs to supply a lower current for a longer duration.

Thanks Malb, i can go the 1000watt motor 2250rpm under load at 48volts its a DC brushed motor so i can run it at

400watts, 800rpm, 3 stage pulley final output 3.5rpm, gives 734nm of torque

With this motor running full power it will read asfollows

1000watts, 2250rpm, 3 stage pulley final output 9.8rpm, gives 974nm of torque

Onething i never thought about with the 500watt and 600watt motors the first drive will be running at full motor speed although the motors are quiet the chain spinning at x speed may be loud rattling sound the idea was to remain as quiet as possible so it can be used at 3am to load the boat up

I ran through all the calculations for a 330-350mm sprocket and as you mentioned i just could'nt get the torque high enough to be even close to working not on a single stage sprocket set, if i were to make a two stage 330-350mm sprocket set it would probably pull insane torque but its quiet an effort to build that size sprocket

You can buy high torque DC motors with reduction boxes already attached

12V / 24V Worm Gear Speed Reducer Gearbox Electric RV Gear Motor High Torque DC | eBay